Query optimization: from 0 to 10 (and up to 5.7)

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6 hour tutorial about query optimization delivered at the #PerconaLive Amsterdam MySQL, NoSQL and Data conference.

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Query optimization: from 0 to 10 (and up to 5.7)

  1. 1. Query Optimization: From 0 to 10 (and up to 5.7) © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) Jaime Crespo Percona Live Europe 2015 -Amsterdam, 21 Sep 2015- dbahire.com/pleu15
  2. 2. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 2 Agenda – First 3 hours 1. Introduction 5. FULLTEXT Search 2. Access Types and Basic Indexing Techniques 6. Joins 3. Break 7. Subqueries 4. Multi-Column Indexing 8. Query Profiling
  3. 3. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 3 Agenda – Last 3 hours 1. General Optimizer Improvements 6. SQL Mode Changes 2. Computed/Virtual Columns 7. GIS Improvements and JSON Type 3. Query Rewrite Plugins 8. Results and Conclusions 4. Break 9. Q&A 5. Optimizer Hints
  4. 4. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 4 INTRODUCTION Query Optimization: From 0 to 10 (and up to 5.7)
  5. 5. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 5 This is me fighting bad query performance ● Sr. Database Administrator at Wikimedia Foundation ● Used to work as a trainer for Oracle (MySQL), as a Consultant (Percona) and as a Freelance administrator (DBAHire.com)
  6. 6. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 6 MySQL Versions • 5.1 no longer has official support • I will be showing you the results on mysql versions 5.5-5.7/10.1 • MySQL 5.7 and MariaDB 10.1 in RC with great new features
  7. 7. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 7 Recently Added Features Related to Query Optimization • Index Condition Pushdown • Subquery Optimizations materialization and semijoin) • IN-to-EXISTS/EXISTS-to-IN • JOIN-to-WHERE • Multi-Range Read • Batched Key Access • Persistent InnoDB Statistics • UNION ALL optimization • Improved GIS support • EXPLAIN FORMAT=JSON • EXPLAIN INSERT/UPDATE/DELETE • Hash Join • New optimizer hints • New cost-based optimizer • Optimizer Trace • Filesort optimizations • Virtual/computed columns and “functional indexes” • New JSON type
  8. 8. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 8 I Already Mentioned Some of Those Topics during the Last Years • Check my presentations here: http://www.slideshare.net/jynus/
  9. 9. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 9 Example Application (I) • Wiktionary (and all Wikimedia project's data) is licensed under the Creative Commons BY-SA-2.5 License and is Copyright its Contributors
  10. 10. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 10 Example Application (II) • OSM Database is licensed under the Open DataBase License and is Copyright OpenStreetMap Contributors
  11. 11. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 11 Install the example databases ● Downloads and instructions at: http://dbahire.com/pleu15 – Requirements: a MySQL or MariaDB installation (MySQL Sandbox is suggested) – The wiktionary and OSM extracts ● Import them by doing: $ bzcat <file> | mysql <database>
  12. 12. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 12 ACCESS TYPES AND BASIC INDEXING TECHNIQUES Query Optimization: From 0 to 10 (and up to 5.7)
  13. 13. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 13 EXPLAIN ● Essential to understand the execution plan of our queries – Works on SELECTs, INSERTs, UPDATEs, REPLACEs, DELETEs and connections – Fully documented on: http://dev.mysql.com/doc/refman/5.6/en/expla in-output.html
  14. 14. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 14 EXPLAIN Example MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM page WHERE page_title = 'Dutch'; +------+-------------+-------+------+---------------+------ +---------+------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +------+-------------+-------+------+---------------+------ +---------+------+------+-------------+ | 1 | SIMPLE | page | ALL | NULL | NULL | NULL | NULL | 90956 | Using where | +------+-------------+-------+------+---------------+------ +---------+------+------+-------------+ 1 row in set (0.00 sec) Difficult to see something Difficult to see something
  15. 15. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 15 EXPLAIN Example (vertical format) MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM page WHERE page_title = 'Dutch'G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: page type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 90956 Extra: Using where 1 row in set (0.00 sec) Use G for vertical formatting Use G for vertical formatting
  16. 16. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 16 EXPLAIN Example (id) MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM page WHERE page_title = 'Dutch'G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: page type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 90956 Extra: Using where 1 row in set (0.00 sec) Indicates hierarchy level, not execution order Indicates hierarchy level, not execution order
  17. 17. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 17 EXPLAIN Example (select_type) MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM page WHERE page_title = 'Dutch'G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: page type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 90956 Extra: Using where 1 row in set (0.00 sec) Not a subquery or a UNION Not a subquery or a UNION
  18. 18. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 18 EXPLAIN Example (table) MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM page WHERE page_title = 'Dutch'G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: page type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 90956 Extra: Using where 1 row in set (0.00 sec) Table scanned for this step Table scanned for this step
  19. 19. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 19 EXPLAIN Example (type) MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM page WHERE page_title = 'Dutch'G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: page type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 90956 Extra: Using where 1 row in set (0.00 sec) All rows are read for this table (FULL TABLE SCAN) All rows are read for this table (FULL TABLE SCAN)
  20. 20. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 20 EXPLAIN Example (rows) MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM page WHERE page_title = 'Dutch'G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: page type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 90956 Extra: Using where 1 row in set (0.00 sec) Estimated number of rows to be read (all table rows) Estimated number of rows to be read (all table rows)
  21. 21. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 21 How to improve performance? ● Let's add an index on page.page_title: MariaDB [nlwiktionary]> ALTER TABLE page ADD INDEX page_title (page_title); Query OK, 0 rows affected (0.19 sec) Records: 0 Duplicates: 0 Warnings: 0 MariaDB [nlwiktionary]> SELECT * FROM page WHERE page_title = 'Dutch'; 1 row in set (0.11 sec)
  22. 22. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 22 Index creation results (type) MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM page WHERE page_title = 'Dutch'G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: page type: ref possible_keys: page_title key: page_title key_len: 257 ref: const rows: 1 Extra: Using index condition 1 row in set (0.00 sec) type: ref means that an equality comparison will be checked against an index and several results could be returned type: ref means that an equality comparison will be checked against an index and several results could be returned
  23. 23. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 23 Index creation results (possible_keys and key) MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM page WHERE page_title = 'Dutch'G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: page type: ref possible_keys: page_title key: page_title key_len: 257 ref: const rows: 1 Extra: Using index condition 1 row in set (0.00 sec) index(es) that the optimizer considered potentially useful, and final index chosen index(es) that the optimizer considered potentially useful, and final index chosen
  24. 24. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 24 Index creation results (ref) MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM page WHERE page_title = 'Dutch'G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: page type: ref possible_keys: page_title key: page_title key_len: 257 ref: const rows: 1 Extra: Using index condition 1 row in set (0.00 sec) Index is compared with a constant, not with another table Index is compared with a constant, not with another table
  25. 25. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 25 Index creation results (rows) MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM page WHERE page_title = 'Dutch'G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: page type: ref possible_keys: page_title key: page_title key_len: 257 ref: const rows: 1 Extra: Using index condition 1 row in set (0.00 sec) Only 1 row read. In this case, estimation is exact (thanks to index dive) Only 1 row read. In this case, estimation is exact (thanks to index dive)
  26. 26. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 26 Index creation results (query time) MariaDB [nlwiktionary]> SELECT * FROM page WHERE page_title = 'Dutch'; 1 row in set (0.00 sec) Query time has been reduced substantially Query time has been reduced substantially
  27. 27. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 27 Types of indexes ● BTREE – B-TREE in MyISAM, B+TREE in InnoDB ● HASH – Only available for MEMORY and NDB ● FULLTEXT – Inverted indexes in MyISAM and InnoDB ● SPATIAL – RTREEs in MyISAM and InnoDB
  28. 28. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 28 Finding “Dutch” with a BTREE EtchEtch NastyNasty BossBoss GolfGolf LeekLeek SchoolSchool AvastAvast FreightFreight LandscapeLandscape RoverRover DutchDutch HarlemHarlem MaelstromMaelstrom WalrusWalrus TABLETABLE IcebergIceberg
  29. 29. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 29 Finding “Dutch” with a BTREE EtchEtch NastyNasty BossBoss GolfGolf LeekLeek SchoolSchool AvastAvast FreightFreight LandscapeLandscape RoverRover DutchDutch HarlemHarlem MaelstromMaelstrom WalrusWalrus TABLETABLE IcebergIceberg
  30. 30. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 30 Do indexes always work? (1/2) ● Can we use an index to make this query faster? SELECT * FROM page WHERE page_title like 'Spa%';
  31. 31. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 31 It is a range MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM page WHERE page_title like 'Spa%'G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: page type: range possible_keys: page_title key: page_title key_len: 257 ref: NULL rows: 94 Extra: Using index condition 1 row in set (0.00 sec) Despite not being an equality, we can use the index to find the values quickly Despite not being an equality, we can use the index to find the values quickly
  32. 32. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 32 BTREE Indexes can be used for ranges, too EtchEtch NastyNasty BossBoss GolfGolf LeekLeek SchoolSchool AvastAvast FreightFreight LandscapeLandscape RoverRover DutchDutch HarlemHarlem MaelstromMaelstrom WalrusWalrus TABLETABLE IcebergIceberg
  33. 33. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 33 Do indexes always work? (2/2) ● What about this other query? SELECT * FROM page WHERE page_title like '%utch';
  34. 34. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 34 Let's check with EXPLAIN MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM page WHERE page_title like '%utch'G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: page type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 93189 Extra: Using where 1 row in set (0.00 sec) No index can be used for filtering. A full table scan is performed. No index can be used for filtering. A full table scan is performed.
  35. 35. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 35 BTREE Index EtchEtch NastyNasty BossBoss GolfGolf LeekLeek SchoolSchool AvastAvast FreightFreight LandscapeLandscape RoverRover DutchDutch HarlemHarlem MaelstromMaelstrom WalrusWalrus TABLETABLE IcebergIceberg ?
  36. 36. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 36 Btree indexes usage ● Filtering – Equality (operator '=') – Ranges (BETWEEN … AND, >, <, >=, <=, like 'prefix%') – “EXISTS” operators: IN, OR on the same column ● Ordering – ORDER BY (indexed columns) – GROUP BY (indexed columns) ● Returning values directly from the index – Covering index – Functions like max(), min(), etc.
  37. 37. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 37 type: const MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM revision WHERE rev_id = 2G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: const possible_keys: PRIMARY key: PRIMARY key_len: 4 ref: const rows: 1 Extra: 1 row in set (0.00 sec) 'const' is a special case of 'ref', when the index can assure that only 1 results can be returned (equality + primary key or unique key). It is faster. 'const' is a special case of 'ref', when the index can assure that only 1 results can be returned (equality + primary key or unique key). It is faster.
  38. 38. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 38 type: NULL MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM revision WHERE rev_id = -1G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: NULL type: NULL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: NULL Extra: Impossible WHERE noticed after reading const tables 1 row in set (0.00 sec) 'NULL' is not really a plan, just an optimization that allow discarding immediately impossible conditions 'NULL' is not really a plan, just an optimization that allow discarding immediately impossible conditions
  39. 39. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 39 type: ref_or_null MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM user WHERE user_email_token = '0' OR user_email_token IS NULLG *************************** 1. row *************************** id: 1 select_type: SIMPLE table: user type: ref_or_null possible_keys: user_email_token key: user_email_token key_len: 33 ref: const rows: 2 Extra: Using index condition; Using where 1 row in set (0.00 sec) Equivalent to 'ref', but also has into account NULL values Equivalent to 'ref', but also has into account NULL values
  40. 40. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 40 type: range (using IN / OR) MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM page WHERE page_title IN ('Dutch', 'English', 'Spanish')G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: page type: range possible_keys: page_title key: page_title key_len: 257 ref: NULL rows: 4 Extra: Using index condition 1 row in set (0.00 sec) Despite being a range, its execution is very different from ranges using like, between or inequality operators Despite being a range, its execution is very different from ranges using like, between or inequality operators
  41. 41. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 41 Is this a bug? (1/2) MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM page WHERE page_namespace = 2G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: page type: ref possible_keys: name_title key: name_title key_len: 4 ref: const rows: 45 Extra: 1 row in set (0.00 sec) An index is used to return pages with ns=2 An index is used to return pages with ns=2
  42. 42. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 42 Is this a bug? (2/2) MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM page WHERE page_namespace = 0G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: page type: ALL possible_keys: name_title key: NULL key_len: NULL ref: NULL rows: 7493 Extra: Using where 1 row in set (0.00 sec) The index is not used with ns=0 The index is not used with ns=0
  43. 43. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 43 Using an index is sometimes suboptimal This point is not fixed, and depends on the hardware and buffer state This point is not fixed, and depends on the hardware and buffer state
  44. 44. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 44 What index should we add to make this query faster? MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM revision WHERE left(rev_timestamp, 6) = '201509'G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 163253 Extra: Using where 1 row in set (0.00 sec)
  45. 45. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 45 The table has already an index on rev_timestamp MariaDB [nlwiktionary]> SHOW CREATE TABLE revisionG *************************** 1. row *************************** Table: revision Create Table: CREATE TABLE `revision` ( ... KEY `rev_timestamp` (`rev_timestamp`),
  46. 46. Optimización de consultas con MySQL 5.6 © 2014 DBAHIRE.COM We need to rewrite the query MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM revision WHERE rev_timestamp >= '201509' and rev_timestamp < '201510'G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: range possible_keys: rev_timestamp key: rev_timestamp key_len: 14 ref: NULL rows: 7 Extra: Using index condition 1 row in set (0.00 sec)
  47. 47. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 47 This transformation is not trivial or even possible in all cases MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM revision WHERE substr(rev_timestamp, 5, 2) = '09'G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL Rows: 173154 Extra: Using where 1 row in set (0.00 sec) Can you think a way to improve this query? Can you think a way to improve this query?
  48. 48. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 48 Indexes for Ordering MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM page ORDER BY page_touched DESC LIMIT 10G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: page type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 8720 Extra: Using filesort 1 row in set (0.00 sec) "Using filesort" indicates that an ordering is needed before returning the results "Using filesort" indicates that an ordering is needed before returning the results
  49. 49. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 49 If that is frequent, we can create an index on page_touched...[nlwiktionary]> ALTER TABLE page ADD INDEX page_page_touched(page_touched); Query OK, 0 rows affected (0.30 sec) Records: 0 Duplicates: 0 Warnings: 0 [nlwiktionary]> EXPLAIN SELECT * FROM page ORDER BY page_touched DESC LIMIT 10G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: page type: index possible_keys: NULL key: page_page_touched key_len: 14 ref: NULL rows: 10 Extra: 1 row in set (0.00 sec) The index does not produce any advantage for filtering The index does not produce any advantage for filtering However, it is very effective by helping avoiding the sort phase However, it is very effective by helping avoiding the sort phase
  50. 50. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 50 It can return data in index order faster EtchEtch NastyNasty BossBoss GolfGolf LeekLeek SchoolSchool AvastAvast FreightFreight LandscapeLandscape RoverRover DutchDutch HarlemHarlem MaelstromMaelstrom WalrusWalrus TABLETABLE IcebergIceberg
  51. 51. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 51 Indexes and GROUP BY (no indexes) MariaDB [nlwiktionary]> EXPLAIN SELECT rev_page, count(*) FROM revision IGNORE INDEX(rev_page_id, page_timestamp, page_user_timestamp) GROUP BY rev_pageG *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 201094 Extra: Using temporary; Using filesort 1 row in set (0.00 sec) Without indexes, a temporary table is created to order results Without indexes, a temporary table is created to order results
  52. 52. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 52 Trick: ORDER BY NULL avoids filesortMariaDB [nlwiktionary]> EXPLAIN SELECT * FROM revision GROUP BY substr(rev_timestamp, 5, 2) = '09'G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 196824 Extra: Using temporary; Using filesort 1 row in set (0.00 sec) MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM revision GROUP BY substr(rev_timestamp, 5, 2) = '09' ORDER BY NULLG *************************** 1. row *************************** ... rows: 196871 Extra: Using temporary 1 row in set (0.00 sec) The advantage is not too big, but it avoids the filesort The advantage is not too big, but it avoids the filesort There is no good index in this case There is no good index in this case
  53. 53. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 53 Indexes and GROUP BY (rev_page_id) MariaDB [nlwiktionary]> EXPLAIN SELECT rev_page, count(*) FROM revision GROUP BY rev_pageG *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: index possible_keys: NULL key: rev_page_id key_len: 8 ref: NULL rows: 192388 Extra: Using index 1 row in set (0.00 sec) The index does not produce any advantage for filtering (there is no WHERE clause) The index does not produce any advantage for filtering (there is no WHERE clause) However, thanks to it we avoid a sort and a temporary table However, thanks to it we avoid a sort and a temporary table
  54. 54. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 54 type: index, loose index scan and covering index (1/3) node_id version k v 234234344545 1 leaves deciduous 234234344546 3 name Northolt Road 234234344548 5 gps:latitude 490018321N 234234344549 6 access uncontrolled 234234344550 1 editor JOSM 234234344551 9 name Big Ben 234234344552 1 source survey 234234344557 1 name London Plane CarlsbergCarlsberg recyclingrecycling Accurate as of 2010 Accurate as of 2010 Gwynne Place Gwynne Place Manor PlaceManor Place treetree 490018321N490018321N deciduousdeciduous London PlaneLondon Plane surveysurvey Big BenBig Ben JOSMJOSM Northolt RoadNortholt Road uncontrolleduncontrolled London Borough of Southwark London Borough of Southwark With 'type:index', all rows are read in index order (full index scan) With 'type:index', all rows are read in index order (full index scan)
  55. 55. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 55 type: index, loose index scan and covering index (2/3) node_id version k v 234234344545 1 leaves deciduous 234234344546 3 name Northolt Road 234234344548 5 gps:latitude 490018321N 234234344549 6 access uncontrolled 234234344550 1 editor JOSM 234234344551 9 name Big Ben 234234344552 1 source survey 234234344557 1 name London Plane CarlsbergCarlsberg recyclingrecycling Accurate as of 2010 Accurate as of 2010 Gwynne Place Gwynne Place Manor PlaceManor Place treetree 490018321N490018321N deciduousdeciduous London PlaneLondon Plane surveysurvey Big BenBig Ben JOSMJOSM Northolt RoadNortholt Road uncontrolleduncontrolled London Borough of Southwark London Borough of Southwark If we have in addition 'Using index for group-by' we have the loose index scan optimization If we have in addition 'Using index for group-by' we have the loose index scan optimization
  56. 56. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 56 Loose Index Scan Example MariaDB [nlwiktionary]> EXPLAIN SELECT rev_page, max(rev_timestamp) FROM revision GROUP BY rev_pageG *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: range possible_keys: NULL key: page_timestamp key_len: 4 ref: NULL rows: 9769 Extra: Using index for group-by 1 row in set (0.00 sec)
  57. 57. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 57 type: index, loose index scan and covering index (3/3) node_id version k v 234234344545 1 leaves deciduous 234234344546 3 name Northolt Road 234234344548 5 gps:latitude 490018321N 234234344549 6 access uncontrolled 234234344550 1 editor JOSM 234234344551 9 name Big Ben 234234344552 1 source survey 234234344557 1 name London Plane CarlsbergCarlsberg recyclingrecycling Accurate as of 2010 Accurate as of 2010 Gwynne Place Gwynne Place Manor PlaceManor Place treetree 490018321N490018321N deciduousdeciduous London PlaneLondon Plane surveysurvey Big BenBig Ben JOSMJOSM Northolt RoadNortholt Road uncontrolleduncontrolled London Borough of Southwark London Borough of Southwark If we have in addition 'Using index' we have the covering index optimization If we have in addition 'Using index' we have the covering index optimization
  58. 58. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 58 Covering Index Example (1/3) MariaDB [nlwiktionary]> ALTER TABLE revision DROP INDEX rev_page_id, drop index page_timestamp, drop index page_user_timestamp; Query OK, 0 rows affected (0.05 sec) Records: 0 Duplicates: 0 Warnings: 0 MariaDB [nlwiktionary]> EXPLAIN SELECT count(DISTINCT rev_user) FROM revision WHERE rev_page = 790G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 218384 Extra: Using where 1 row in set (0.00 sec) MariaDB [nlwiktionary]> SELECT count(DISTINCT rev_user) FROM revision WHERE rev_page = 790G *************************** 1. row *************************** count(DISTINCT rev_user): 1 1 row in set (0.06 sec) Let's start with no indexesLet's start with no indexes
  59. 59. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 59 Covering Index Example (2/3) MariaDB [nlwiktionary]> ALTER TABLE revision ADD INDEX revision_rev_page(rev_page); Query OK, 0 rows affected (0.44 sec) Records: 0 Duplicates: 0 Warnings: 0 MariaDB [nlwiktionary]> EXPLAIN SELECT count(DISTINCT rev_user) FROM revision WHERE rev_page = 790G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: ref possible_keys: revision_rev_page key: revision_rev_page key_len: 4 ref: const rows: 4863 Extra: 1 row in set (0.00 sec) MariaDB [nlwiktionary]> SELECT count(DISTINCT rev_user) FROM revision WHERE rev_page = 790G *************************** 1. row *************************** count(DISTINCT rev_user): 1 1 row in set (0.01 sec) Adding an index on rev_page increases the speed due to improved filtering Adding an index on rev_page increases the speed due to improved filtering
  60. 60. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 60 Covering Index Example (3/3) MariaDB [nlwiktionary]> ALTER TABLE revision ADD INDEX revision_rev_page_rev_user(rev_page, rev_user); Query OK, 0 rows affected (1.48 sec) Records: 0 Duplicates: 0 Warnings: 0 MariaDB [nlwiktionary]> EXPLAIN SELECT count(DISTINCT rev_user) FROM revision WHERE rev_page = 790G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: ref possible_keys: revision_rev_page,revision_rev_page_rev_user key: revision_rev_page_rev_user key_len: 4 ref: const rows: 4863 Extra: Using index 1 row in set (0.00 sec) MariaDB [nlwiktionary]> SELECT count(DISTINCT rev_user) FROM revision WHERE rev_page = 790G *************************** 1. row *************************** count(DISTINCT rev_user): 1 1 row in set (0.00 sec) rev_page, rev_user does not increase the index selectiveness, but allow to return results directly from the index rev_page, rev_user does not increase the index selectiveness, but allow to return results directly from the index The speed difference can be hugeThe speed difference can be huge
  61. 61. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 61 MULTI-COLUMN INDEXES Query Optimization: From 0 to 10 (and up to 5.7)
  62. 62. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 62 In many cases, conditions are applied on more than one column MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM revision WHERE rev_page = 790 and rev_timestamp < '2008'G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 686822 Extra: Using where 1 row in set (0.00 sec) Assuming there were no previously created indexes, which would the optimal one be? Assuming there were no previously created indexes, which would the optimal one be?
  63. 63. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 63 Options for indexes ● 1 index on column (rev_page) ● 1 index on column (rev_timestamp) ● 2 indexes, 1 on (rev_page) and another on (rev_timestamp) ● 1 multi-column index on (rev_page, rev_timestamp) ● 1 multi-column index on (rev_timestamp,rev_page) Are these last 2 different from each other? Would it depend on the query order? Are these last 2 different from each other? Would it depend on the query order?
  64. 64. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 64 A brief reminder about query parsing SELECT * FROM revision WHERE rev_page = 790 and rev_timestamp < '2008' SELECTSELECT FieldsFields FROMFROM revision. rev_page revision. rev_page == (int constant) 790 (int constant) 790 revision. rev_timest amp revision. rev_timest amp << (string constant) '2008' (string constant) '2008' WHEREWHERE revision. rev_id revision. rev_id ... revisio n revisio n Order in the query is not important Order in the query is not important
  65. 65. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 65 Index on (rev_page) MariaDB [nlwiktionary]> ALTER TABLE revision ADD INDEX rev_page (rev_page); Query OK, 0 rows affected (2.31 sec) Records: 0 Duplicates: 0 Warnings: 0 MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM revision WHERE rev_page = 790 and rev_timestamp < '2008'G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: ref possible_keys: rev_page key: rev_page key_len: 4 ref: const rows: 4863 Extra: Using where 1 row in set (0.00 sec) Query time improves significantly with this index Query time improves significantly with this index Less rows are scanned Less rows are scanned
  66. 66. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 66 Adding (rev_timestamp) MariaDB [nlwiktionary]> ALTER TABLE revision ADD INDEX rev_timestamp (rev_timestamp); Query OK, 0 rows affected (1.77 sec) Records: 0 Duplicates: 0 Warnings: 0 MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM revision WHERE rev_page = 790 and rev_timestamp < '2008'G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: ref possible_keys: rev_page,rev_timestamp key: rev_page key_len: 4 ref: const rows: 4863 Extra: Using where 1 row in set (0.01 sec) rev_page is preferred over rev_timestamp rev_page is preferred over rev_timestamp In general, only one index can be used per table access In general, only one index can be used per table access
  67. 67. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 67 Forcing the use of (rev_timestamp) MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM revision FORCE INDEX(rev_timestamp) WHERE rev_page = 790 and rev_timestamp < '2008'G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: range possible_keys: rev_timestamp key: rev_timestamp key_len: 14 ref: NULL rows: 343411 Extra: Using index condition; Using where 1 row in set (0.00 sec) It is a range access It is a range access A lot more accessed rowsA lot more accessed rows Forcing the index is worse than type:ALL!Forcing the index is worse than type:ALL!
  68. 68. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 68 Adding (rev_page, rev_timestamp)MariaDB [nlwiktionary]> ALTER TABLE revision ADD INDEX rev_page_rev_timestamp(rev_page, rev_timestamp); Query OK, 0 rows affected (1.59 sec) Records: 0 Duplicates: 0 Warnings: 0 MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM revision WHERE rev_page = 790 and rev_timestamp < '2008'G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: range possible_keys: rev_page,rev_timestamp,rev_page_rev_timestamp key: rev_page_rev_timestamp key_len: 18 ref: NULL rows: 1048 Extra: Using index condition 1 row in set (0.00 sec) Reduced number of rows scanned Reduced number of rows scanned
  69. 69. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 69 Is (rev_timestamp, rev_page) a better option?MariaDB [nlwiktionary]> ALTER TABLE revision ADD INDEX rev_timestamp_rev_page (rev_timestamp, rev_page); Query OK, 0 rows affected (1.76 sec) Records: 0 Duplicates: 0 Warnings: 0 MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM revision WHERE rev_page = 790 and rev_timestamp < '2008'G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: range possible_keys: rev_page,rev_timestamp,rev_page_rev_timestamp,rev_timestamp_rev_page key: rev_page_rev_timestamp key_len: 18 ref: NULL rows: 1048 Extra: Using index condition 1 row in set (0.00 sec) Previous index is still preferred, why?
  70. 70. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 70 Forcing (rev_timestamp, rev_page) MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM revision FORCE INDEX(rev_timestamp_rev_page) WHERE rev_page = 790 and rev_timestamp < '2008'G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: range possible_keys: rev_timestamp_rev_page key: rev_timestamp_rev_page key_len: 18 ref: NULL rows: 343411 Extra: Using index condition 1 row in set (0.00 sec) Only the first column is being used effectively for filtering
  71. 71. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 71 A compound index produces a single tree ordered by the 2 values (23443, 2)(23443, 2) (790, '2010')(790, '2010') (54005, '2016') (54005, '2016') (15444, '2011') (15444, '2011') (790, '2012')(790, '2012') (790, '2007')(790, '2007') (84611, '2015')(84611, '2015') (21702, '2014')(21702, '2014') (1024, '2003')(1024, '2003') (790, '2008')(790, '2008') (46771, '2013')(46771, '2013') (13605, '2006')(13605, '2006') (790, '2011')(790, '2011') (105, '2015')(105, '2015') TABLETABLE (12301, 1)(12301, 1) rev_page = 790 and rev_timestamp < '2008' (rev_page, rev_timestamp) (rev_page, rev_timestamp)
  72. 72. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 72 The alternative index cannot be used in such an effective way ('2008', 800)('2008', 800) ('2004', 24)('2004', 24) ('2014', 107)('2014', 107) ('2008', 155)('2008', 155) ('2004', 999)('2004', 999) ('2001', 276)('2001', 276) ('2015', 355)('2015', 355) ('2008', 790)('2008', 790) ('2005', 791)('2005', 791) ('2002', 205)('2002', 205) ('2010', 206)('2010', 206) ('2007', 201)('2007', 201) ('2004', 790)('2004', 790) ('2001', 105)('2001', 105) TABLETABLE ('2006', 13605) ('2006', 13605) (rev_timestamp, rev_page) (rev_timestamp, rev_page) rev_page = 790 and rev_timestamp < '2008'
  73. 73. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 73 Order and column selection • Range access using >, <, >=, <=, BETWEEN can only be filtered once effectively, at the end of an index • When selecting indexes, prefer columns with high cardinality (very selective) – The optimal index can depend on the constants used
  74. 74. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 74 Use of "Handler_*" statistics • They are post-execution statistics at row level – Unlike EXPLAIN's "rows" column, they are exact, not a guess – They allow to compare query execution performance in a deterministic way, independently of the execution time
  75. 75. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 75 "Handler" Stats (indexed) mysql> SHOW SESSION STATUS like 'Hand%'; +----------------------------+----------+ | Variable_name | Value | +----------------------------+----------+ | Handler_commit | 80 | | Handler_delete | 0 | | Handler_discover | 0 | | Handler_external_lock | 166 | | Handler_mrr_init | 0 | | Handler_prepare | 0 | | Handler_read_first | 23 | | Handler_read_key | 736212 | | Handler_read_last | 0 | | Handler_read_next | 22208001 | | Handler_read_prev | 0 | | Handler_read_rnd | 665215 | | Handler_read_rnd_next | 14223297 | | Handler_rollback | 0 | | Handler_savepoint | 0 | | Handler_savepoint_rollback | 0 | | Handler_update | 66970 | | Handler_write | 2869409 | +----------------------------+----------+ 18 rows in set (0.00 sec) Number of times that the first entry of an index was read. It may indicate the number of full index scans Number of times that the first entry of an index was read. It may indicate the number of full index scans Number of time a row has been retrieved using an index Number of time a row has been retrieved using an index Next row has been requested in index order (typical for index scans or ranges) Next row has been requested in index order (typical for index scans or ranges)
  76. 76. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 76 "Handler" Stats (unindexed) mysql> SHOW SESSION STATUS like 'Hand%'; +----------------------------+----------+ | Variable_name | Value | +----------------------------+----------+ | Handler_commit | 80 | | Handler_delete | 0 | | Handler_discover | 0 | | Handler_external_lock | 166 | | Handler_mrr_init | 0 | | Handler_prepare | 0 | | Handler_read_first | 23 | | Handler_read_key | 736212 | | Handler_read_last | 0 | | Handler_read_next | 22208001 | | Handler_read_prev | 0 | | Handler_read_rnd | 665215 | | Handler_read_rnd_next | 14223297 | | Handler_rollback | 0 | | Handler_savepoint | 0 | | Handler_savepoint_rollback | 0 | | Handler_update | 66970 | | Handler_write | 2869409 | +----------------------------+----------+ 18 rows in set (0.00 sec) A row has been requested in a specific position (typical for joins or order by without indexes) A row has been requested in a specific position (typical for joins or order by without indexes) Request tp read the next row in “table order” (typical for full table scans) Request tp read the next row in “table order” (typical for full table scans) Insertions in SELECTS may indicate temporary tables Insertions in SELECTS may indicate temporary tables
  77. 77. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 77 Comparing statistics of the previous indexes (no indexes)MariaDB [nlwiktionary]> FLUSH STATUS; Query OK, 0 rows affected (0.00 sec) MariaDB [nlwiktionary]> SELECT * FROM revision IGNORE INDEX(rev_page, rev_timestamp, rev_page_rev_timestamp, rev_timestamp_rev_page) WHERE rev_page = 790 and rev_timestamp < '2008'; 1049 rows in set (0.58 sec) MariaDB [nlwiktionary]> SHOW STATUS like 'Hand%'; +----------------------------+--------+ | Variable_name | Value | +----------------------------+--------+ | Handler_commit | 1 | | Handler_delete | 0 | … | Handler_read_first | 0 | | Handler_read_key | 0 | | Handler_read_last | 0 | | Handler_read_next | 0 | | Handler_read_prev | 0 | | Handler_read_rnd | 0 | | Handler_read_rnd_deleted | 0 | | Handler_read_rnd_next | 820309 | | Handler_rollback | 0 | … | Handler_update | 0 | | Handler_write | 0 | +----------------------------+--------+ 25 rows in set (0.00 sec) Typical result for a full table scan Typical result for a full table scan
  78. 78. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 78 Index on (rev_page) MariaDB [nlwiktionary]> SHOW STATUS like 'Hand%'; +----------------------------+-------+ | Variable_name | Value | +----------------------------+-------+ | Handler_commit | 1 | | Handler_delete | 0 | … | Handler_read_first | 0 | | Handler_read_key | 1 | | Handler_read_last | 0 | | Handler_read_next | 4864 | | Handler_read_prev | 0 | | Handler_read_rnd | 0 | | Handler_read_rnd_deleted | 0 | | Handler_read_rnd_next | 0 | | Handler_rollback | 0 | … | Handler_update | 0 | | Handler_write | 0 | +----------------------------+-------+ 25 rows in set (0.01 sec) Then, scan them one by one in index order Then, scan them one by one in index order Using the index, request the first row with rev_page=790 Using the index, request the first row with rev_page=790
  79. 79. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 79 Index on (rev_timestamp) MariaDB [nlwiktionary]> SHOW STATUS like 'Hand%'; +----------------------------+---------+ | Variable_name | Value | +----------------------------+---------+ | Handler_commit | 1 | | Handler_delete | 0 | … | Handler_read_first | 0 | | Handler_read_key | 1 | | Handler_read_last | 0 | | Handler_read_next | 199155 | | Handler_read_prev | 0 | | Handler_read_rnd | 0 | | Handler_read_rnd_deleted | 0 | | Handler_read_rnd_next | 0 | | Handler_rollback | 0 | … | Handler_update | 0 | | Handler_write | 0 | +----------------------------+---------+ 25 rows in set (0.00 sec) Then, scan them one by one in index order (more are matched) Then, scan them one by one in index order (more are matched) Using the index, request the first row where rev_timestamp<2008 Using the index, request the first row where rev_timestamp<2008 Let's ignore ICP for nowLet's ignore ICP for now
  80. 80. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 80 Index on (rev_page, rev_timestamp)MariaDB [nlwiktionary]> SHOW STATUS like 'Hand%'; +----------------------------+-------+ | Variable_name | Value | +----------------------------+-------+ | Handler_commit | 1 | | Handler_delete | 0 | … | Handler_read_first | 0 | | Handler_read_key | 1 | | Handler_read_last | 0 | | Handler_read_next | 1049 | | Handler_read_prev | 0 | | Handler_read_rnd | 0 | | Handler_read_rnd_deleted | 0 | | Handler_read_rnd_next | 0 | | Handler_rollback | 0 | … | Handler_update | 0 | | Handler_write | 0 | +----------------------------+-------+ 25 rows in set (0.00 sec) Rows scanned == Rows returnedRows scanned == Rows returned With both conditions covered, we can find the actual first row that matches the condition using the index With both conditions covered, we can find the actual first row that matches the condition using the index
  81. 81. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 81 Index on (rev_timestamp, rev_page), no ICPMariaDB [nlwiktionary]> SHOW STATUS like 'Hand%'; +----------------------------+---------+ | Variable_name | Value | +----------------------------+---------+ | Handler_commit | 1 | | Handler_delete | 0 | … | Handler_read_first | 0 | | Handler_read_key | 1 | | Handler_read_last | 0 | | Handler_read_next | 199155 | | Handler_read_prev | 0 | | Handler_read_rnd | 0 | | Handler_read_rnd_deleted | 0 | | Handler_read_rnd_next | 0 | | Handler_rollback | 0 | … | Handler_update | 0 | | Handler_write | 0 | +----------------------------+---------+ 25 rows in set (0.00 sec) Assuming no ICP, exact same results than with (rev_timestamp). The extra column does not help. Also, EXPLAIN's row count was very off. Assuming no ICP, exact same results than with (rev_timestamp). The extra column does not help. Also, EXPLAIN's row count was very off.
  82. 82. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 82 Redundant Indexes ● Creating all 4 previous indexes in production is not a great idea – "Left-most index prefix" allows, for example (rev_page, rev_timestamp) doing everything you can do with (rev_page) – If two indexes have equal selectivity, MySQL chooses the shortest one
  83. 83. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 83 "Left-most index" Example MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM revision FORCE INDEX(rev_page_rev_timestamp) WHERE rev_page = 790G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: ref possible_keys: rev_page_rev_timestamp key: rev_page_rev_timestamp key_len: 4 ref: const rows: 4863 Extra: 1 row in set (0.00 sec) Only the first column is usedOnly the first column is used
  84. 84. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 84 Duplicate Indexes ● It is very easy to create indexes with the same exact definition (same columns and ordering) – Set a convention for index naming (e.g tablename_column1_column2_idx) – MySQL does not allow 2 indexes with the same identifier – Since MySQL 5.6, an warning is thrown if a duplicate index is created
  85. 85. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 85 pt-duplicate-index-checker $ pt-duplicate-key-checker h=127.0.0.1,P=5621,u=msandbox,p=msandbox […] # rev_timestamp is a left-prefix of rev_timestamp_rev_page # Key definitions: # KEY `rev_timestamp` (`rev_timestamp`), # KEY `rev_timestamp_rev_page` (`rev_timestamp`,`rev_page`) # Column types: # `rev_timestamp` binary(14) not null default '00000000000000' # `rev_page` int(10) unsigned not null # To remove this duplicate index, execute: ALTER TABLE `nlwiktionary`.`revision` DROP INDEX `rev_timestamp`; # rev_page is a left-prefix of rev_page_rev_timestamp # Key definitions: # KEY `rev_page` (`rev_page`), # KEY `rev_page_rev_timestamp` (`rev_page`,`rev_timestamp`), # Column types: # `rev_page` int(10) unsigned not null # `rev_timestamp` binary(14) not null default '00000000000000' # To remove this duplicate index, execute: ALTER TABLE `nlwiktionary`.`revision` DROP INDEX `rev_page`; # ###################################################### Summary of indexes ######################################## # Size Duplicate Indexes 15478317 # Total Duplicate Indexes 4 # Total Indexes 285 Simple tool to check redundant and duplicate indexes Simple tool to check redundant and duplicate indexes
  86. 86. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 86 "OR"-style conditions over the same column MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM revision WHERE rev_page = 790 OR rev_page = 795 OR rev_page = 1024G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: range possible_keys: rev_page,rev_page_rev_timestamp key: rev_page key_len: 4 ref: NULL rows: 4890 Extra: Using index condition; Using where 1 row in set (0.01 sec) Equivalent to: SELECT * FROM revision WHERE rev_page IN (790, 795, 1024) Equivalent to: SELECT * FROM revision WHERE rev_page IN (790, 795, 1024)
  87. 87. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 87 Handlers on "IN" / "OR" conditions over the same column+----------------------------+-------+ | Variable_name | Value | +----------------------------+-------+ | Handler_commit | 1 | | Handler_delete | 0 | … | Handler_prepare | 0 | | Handler_read_first | 0 | | Handler_read_key | 3 | | Handler_read_last | 0 | | Handler_read_next | 4891 | | Handler_read_prev | 0 | | Handler_read_rnd | 0 | | Handler_read_rnd_deleted | 0 | | Handler_read_rnd_next | 0 | | Handler_rollback | 0 | … | Handler_update | 0 | | Handler_write | 0 | +----------------------------+-------+ 25 rows in set (0.00 sec) Despite identifying themselves as “range”s, the execution is slightly different, one index dive (similar to a ref) is done per value. This can be an issue in conditions with thousands of items. Despite identifying themselves as “range”s, the execution is slightly different, one index dive (similar to a ref) is done per value. This can be an issue in conditions with thousands of items.
  88. 88. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 88 "OR"-style conditions over different columns ● We cannot use a single index efficiently for both conditions – We can scan both conditions separatelly and mix the results, discarding duplicates – Or use an index for one condition and not for the other – Index merge allows to use two indexes for a single table access simultaneously
  89. 89. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 89 Index Merge Example MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM revision WHERE rev_page = 790 or rev_timestamp < '2004'G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: index_merge possible_keys: rev_page,rev_timestamp,rev_page_rev_timestamp, rev_timestamp_rev_page key: rev_page,rev_timestamp key_len: 4,14 ref: NULL rows: 4871 Extra: Using sort_union(rev_page,rev_timestamp); Using where 1 row in set (0.00 sec) Both indexes are used, then combined using the "union" operation Both indexes are used, then combined using the "union" operation
  90. 90. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 90 INDEX_MERGE Issues ● Sometimes it is faster to to execute the sentence using UNION: – This is specially true with (UNION ALL) since MySQL 5.7, if you do not care about duplicates ● There are also interseccion merges, but multi-column indexes are preferred
  91. 91. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 91 Disabling optimizer features (I) ● The optimizer_switch variable allows enabling and disablig globally or per session many query optimizer features: MariaDB [nlwiktionary]> SHOW VARIABLES like 'optimizer_switch'G *************************** 1. row *************************** Variable_name: optimizer_switch Value: index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersec tion=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_cond ition_pushdown=on,derived_merge=on,derived_with_keys=on,firstmatch=on,loosescan=on ,materialization=on,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,parti al_match_table_scan=on,subquery_cache=on,mrr=off,mrr_cost_based=off,mrr_sort_keys= off,outer_join_with_cache=on,semijoin_with_cache=on,join_cache_incremental=on,join _cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=off,table_elimination =on,extended_keys=on,exists_to_in=on 1 row in set (0.00 sec)
  92. 92. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 92 Deshabilitar características del optimizador (II)MariaDB [nlwiktionary]> SET optimizer_switch='index_merge_sort_union=off'; Query OK, 0 rows affected (0.00 sec) MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM revision WHERE rev_page = 790 or rev_timestamp < '2004'G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: ALL possible_keys: rev_page,rev_timestamp,rev_page_rev_timestamp,rev_timestamp_rev_page key: NULL key_len: NULL ref: NULL rows: 686822 Extra: Using where 1 row in set (0.00 sec) This will only have effect for the current session. This will only have effect for the current session.
  93. 93. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 93 What happens if we have two ranges? ● As seen previously, we cannot use efficiently two range types on the same table access. Alternatives: – Use only one index for the most selective column – Use index condition pushdown to get an advantage – Change one of the two ranges into a discrete "IN" comparison/bucketize with a new column – Use quadtrees or R-TREEs (spatial indexing)
  94. 94. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 94 Example of Bucketizing (I) MariaDB [nlwiktionary]> EXPLAIN SELECT count(*) FROM revision WHERE rev_timestamp < '2008' AND rev_len > 5500G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: ALL possible_keys: rev_timestamp,rev_timestamp_rev_page key: NULL key_len: NULL ref: NULL rows: 686822 Extra: Using where 1 row in set (0.00 sec) Looks like only an index on (rev_timestamp) or (rev_len) would be useful as we have 2 ranges. Looks like only an index on (rev_timestamp) or (rev_len) would be useful as we have 2 ranges.
  95. 95. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 95 Example of Bucketizing (II) MariaDB [nlwiktionary]> ALTER TABLE revision ADD COLUMN rev_len_cat int; Query OK, 0 rows affected (38.28 sec) Records: 0 Duplicates: 0 Warnings: 0 MariaDB [nlwiktionary]> UPDATE revision set rev_len_cat = IF(rev_len < 10000, rev_len div 1000, 10); Query OK, 820308 rows affected (15.19 sec) Rows matched: 820308 Changed: 820308 Warnings: 0 MariaDB [nlwiktionary]> ALTER TABLE revision ADD INDEX rev_len_cat_rev_timestamp (rev_len_cat, rev_timestamp); Query OK, 0 rows affected (2.11 sec) Records: 0 Duplicates: 0 Warnings: 0
  96. 96. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 96 Example of Bucketizing (III) MariaDB [nlwiktionary]> EXPLAIN SELECT count(*) FROM revision WHERE rev_timestamp < '2008' AND rev_len > 5500 AND rev_len_cat IN (5, 6, 7, 8, 9, 10)G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: range possible_keys: rev_timestamp,rev_timestamp_rev_page,rev_len_cat_rev_timestamp key: rev_len_cat_rev_timestamp key_len: 19 ref: NULL rows: 4442 Extra: Using where 1 row in set (0.00 sec) We did some transformations to both the structure and the query. We did some transformations to both the structure and the query.
  97. 97. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 97 Example of Index Condition PushdownMariaDB [nlwiktionary]> ALTER TABLE revision ADD INDEX rev_len_rev_timestamp(rev_len, rev_timestamp); Query OK, 0 rows affected (1.77 sec) Records: 0 Duplicates: 0 Warnings: 0 MariaDB [nlwiktionary]> SET optimizer_switch='index_condition_pushdown=on'; EXPLAIN SELECT * FROM revision WHERE rev_timestamp < '2008' AND rev_len > 5500G Query OK, 0 rows affected (0.00 sec) *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: range possible_keys: rev_timestamp,rev_timestamp_rev_page,rev_len_rev_timestamp key: rev_len_rev_timestamp key_len: 5 ref: NULL rows: 38744 Extra: Using index condition 1 row in set (0.00 sec) Index condition pushdown (ICP) eanbles the engines to use extra parts of the index while avoiding costly row movements to and from the SQL layer Index condition pushdown (ICP) eanbles the engines to use extra parts of the index while avoiding costly row movements to and from the SQL layer
  98. 98. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 98 ICP Issues ● Differences in execution time is more significative when the extra column condition is very selective (getting 5x the original performance) ● ICP is ignored when using covering Index, making the performance worse
  99. 99. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 99 Does LIMIT improve the performance? (I) MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM page ORDER BY page_touchedG *************************** 1. row *************************** type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 90956 Extra: Using filesort MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM page ORDER BY page_touched LIMIT 10G *************************** 1. row *************************** type: index possible_keys: NULL key: page_page_touched key_len: 14 ref: NULL rows: 10 Extra: 1 row in set (0.00 sec) In some cases it can be essential to allow effective usage of the indexes In some cases it can be essential to allow effective usage of the indexes
  100. 100. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 100 Does LIMIT improve the performance? (II)MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM revision ORDER BY rev_commentG *************************** 1. row *************************** [...] type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 817636 Extra: Using filesort 1 row in set (0.00 sec) MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM revision ORDER BY rev_comment LIMIT 10G *************************** 1. row *************************** […] table: revision type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 817636 Extra: Using filesort 1 row in set (0.00 sec) In other cases, it has no effect on the scanned rows (just on the returned ones) In other cases, it has no effect on the scanned rows (just on the returned ones)
  101. 101. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 101 Does LIMIT improve the performance? (I)MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM page ORDER BY page_title LIMIT 100G *************************** 1. row *************************** type: index possible_keys: NULL key: page_title key_len: 257 ref: NULL rows: 100 Extra: 1 row in set (0.00 sec) MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM page ORDER BY page_title LIMIT 10000, 100G *************************** 1. row *************************** type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 90956 Extra: Using filesort 1 row in set (0.00 sec) In this case, performance will vary depending on the offset (not ideal) In this case, performance will vary depending on the offset (not ideal)
  102. 102. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 102 Can we filter and sort at the same time using indexes? MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM revision WHERE rev_comment='' ORDER BY rev_timestamp ASCG *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 817636 Extra: Using where; Using filesort 1 row in set (0.00 sec) This query is slow because a) the full table scan This query is slow because a) the full table scan b) Required sort after filtering b) Required sort after filtering
  103. 103. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 103 Adding and index on (rev_comment, rev_timestamp)MariaDB [nlwiktionary]> ALTER TABLE revision ADD INDEX rev_comment_rev_timestamp (rev_comment, rev_timestamp); Query OK, 0 rows affected (3.19 sec) Records: 0 Duplicates: 0 Warnings: 0 MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM revision WHERE rev_comment='' ORDER BY rev_timestamp ASCG *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: ref possible_keys: rev_comment_rev_timestamp key: rev_comment_rev_timestamp key_len: 769 ref: const rows: 266462 Extra: Using index condition; Using where 1 row in set (0.00 sec) Both type: ALL and filesort have disappeared Both type: ALL and filesort have disappeared
  104. 104. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 104 This is not always possible MariaDB [nlwiktionary]> EXPLAIN SELECT * FROM revision WHERE rev_len > 5500 ORDER BY rev_timestamp ASCG *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: range possible_keys: rev_len_rev_timestamp key: rev_len_rev_timestamp key_len: 5 ref: NULL rows: 38744 Extra: Using index condition; Using filesort 1 row in set (0.00 sec) The range makes impossible to use the index optimally for the the ORDER BY: either we filter (rev_len) or sort (rev_timestamp) The range makes impossible to use the index optimally for the the ORDER BY: either we filter (rev_len) or sort (rev_timestamp)
  105. 105. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 105 A Strange Game. The Only Winning Move is Not to Play mysql-5.6.21 (osm) > SELECT * FROM nodes FORCE INDEX(version_idx) WHERE version < 15 ORDER BY changeset_id; /* type: range, Using filesort */ 2859673 rows in set (30.58 sec) mysql-5.6.21 (osm) > SELECT * FROM nodes FORCE INDEX(changeset_id_idx) WHERE version < 15 ORDER BY changeset_id; /* type: index */ 2859673 rows in set (30.92 sec) mysql-5.6.21 (osm) > SELECT * FROM nodes WHERE version < 15 ORDER BY changeset_id; /* type: ALL, Using filesort */ 2859673 rows in set (16.54 sec)
  106. 106. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 106 MyISAM Internals node_id versio k v 234234344545 1 leaves deciduous (empty row) 234234344548 5 gps:latitude 490018321N 234234344549 6 access uncontrolled (empty row) 234234344551 9 name Big Ben 234234344552 1 source survey 234234344557 1 name London Plane 234234344552 2 source survey 234234344557 2 name London Plane CarlsbergCarlsberg recyclingrecycling Accurate as of 2010 Accurate as of 2010 Gwynne Place Gwynne Place Manor PlaceManor Place treetree 490018321N490018321N deciduousdeciduous London PlaneLondon Plane surveysurvey Big BenBig Ben JOSMJOSM Northolt RoadNortholt Road uncontrolleduncontrolled London Borough of Southwark London Borough of Southwark Data (revision.MYD)Index (part of revision.MYI)
  107. 107. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 107 InnoDB Internals (PRIMARY) Data clustered always using the primary key Data clustered always using the primary key 244 208 105 476 356 702 605 811 771 702 476 244 version k v 1 leaves deciduous 3 name Northolt Road 5 gps:latitu 490018321N 6 access uncontrolled 1 editor JOSM 9 name Big Ben 2 source survey 1 name London Plane 7 amenity pub
  108. 108. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 108 InnoDB Internals (Secondary) 6 3 1 1 1 1 3 2 6 5 9 7 PK 356 105 702 811 476 208 Secondary indexes contain the primary key value Secondary indexes contain the primary key value PK / Datosíndice (version) 244 208 105 476 356 702 605 811 771 702 476 244 version k v 1 leaves deciduous 3 name Northolt Road 5 gps:latitu 490018321N 6 access uncontrolled 1 editor JOSM 9 name Big Ben 2 source survey 1 name London Plane 7 amenity pub 605 244 771
  109. 109. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 109 Consequences of using InnoDB (I) ● Every table should have a primary key – If one is not defined, MySQL will choose an available NOT NULL unique key – If that is not possible, an internal 6-byte row identifier will be generated (not user-accesible)
  110. 110. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 110 Consequences of using InnoDB (II) ● Inserting in primary key order is much faster – Less fragmentation/page-split – Usage of "batch" mode, improving insert speed ● Using auto-increment keys as primary keys can be a good idea for InnoDB
  111. 111. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 111 Consequences of using InnoDB (III) • A very long primary key may increment substantially the size of secondary keys – Int or bigint types are recommended instead of UUIDs or other long strings
  112. 112. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 112 Differences in size mysql-5.6.21 (osm) > CREATE TABLE pk_int (id int PRIMARY KEY auto_increment, a int, b int, c int, d int); Query OK, 0 rows affected (0.16 sec) mysql-5.6.21 (osm) > CREATE TABLE pk_uuid (id char(36) PRIMARY KEY, a int, b int, c int, d int); Query OK, 0 rows affected (0.04 sec) pk_int pk_uuid 0 8500000 17000000 25500000 34000000 42500000 12,582,912 20,971,520 13,631,488 32,505,856 .ibd size (no secondary indexes) .ibd size (with secondary indexes) bytes
  113. 113. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 113 Extended primary key optimization ● As the primary key is part of all seconady keys, this can be used “for free”: – For row filtering (since MySQL 5.6) – To return results in primary key order – To avoid reading data from the table (covering index)
  114. 114. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 114 Extended Primary Key Example mysql-5.6.21 (osm) > EXPLAIN SELECT node_id FROM nodes WHERE changeset_id = 24284 and node_id <> 146472942G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: nodes type: range possible_keys: PRIMARY,changeset_id_idx key: changeset_id_idx key_len: 16 ref: NULL rows: 50 Extra: Using where; Using index 1 row in set (0.07 sec)
  115. 115. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 115 FULLTEXT SEARCH Query Optimization: From 0 to 10 (and up to 5.7)
  116. 116. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 116 Fuzzy Search of “gloucester/Gloucester’s/etc” ● “Typical” way to solve this: mysql-5.7.5 (osm) > SELECT way_id as id, v FROM way_tags WHERE v like '%gloucester%'; 425 rows in set (0.46 sec) Too slowToo slow
  117. 117. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 117 Let’s Add an Index mysql-5.7.5 (osm) > ALTER TABLE way_tags ADD INDEX(v); Query OK, 0 rows affected (6.44 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql-5.7.5 (osm) > SELECT ...; 425 rows in set (0.38 sec) mysql-5.7.5 (osm) > EXPLAIN SELECT way as type, way_id as id, v FROM way_tags WHERE v like '%gloucester%'; +----+.+-------+---------------+------+---------+------+---------+----------+--------------------------+ | id |.| type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+.+-------+---------------+------+---------+------+---------+----------+--------------------------+ | 1 |.| index | NULL | v_2 | 767 | NULL | 1333338 | 11.11 | Using where; Using index | +----+.+-------+---------------+------+---------+------+---------+----------+--------------------------+ 1 row in set, 1 warning (0.01 sec) Still slow, why?Still slow, why?
  118. 118. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 118 Fulltext Index mysql-5.7.5 (osm) > ALTER TABLE way_tags add FULLTEXT index(v); Query OK, 0 rows affected (3.20 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql-5.7.5 (osm) > SELECT ...; 425 rows in set (0.00 sec) mysql-5.7.5 (osm) > EXPLAIN SELECT 'way' as type, way_id as id, v FROM way_tags WHERE MATCH(v) AGAINST ('+gloucester*' IN BOOLEAN MODE); +----+.+----------+---------------+------+---------+-------+------+----------+-----------------------------------+ | id |.| type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+.+----------+---------------+------+---------+-------+------+----------+-----------------------------------+ | 1 |.| fulltext | v | v | 0 | const | 1 | 100.00 | Using where; Ft_hints: no_ranking | +----+.+----------+---------------+------+---------+-------+------+----------+-----------------------------------+ 1 row in set, 1 warning (0.00 sec)
  119. 119. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 119 Newer Fulltext Optimizations mysql-5.5.40 (osm) > EXPLAIN SELECT count(*) FROM way_tags_myisam WHERE MATCH(v) AGAINST('gloucester'); +----+-------------+-----------------+----------+---------------+------+---------+------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-----------------+----------+---------------+------+---------+------+------+-------------+ | 1 | SIMPLE | way_tags_myisam | fulltext | v | v | 0 | | 1 | Using where | +----+-------------+-----------------+----------+---------------+------+---------+------+------+-------------+ 1 row in set (0.00 sec) mysql-5.5.40 (osm) > SHOW STATUS like 'Hand%'; +----------------------------+-------+ | Variable_name | Value | +----------------------------+-------+ | Handler_commit | 0 | | Handler_delete | 0 | ... | Handler_read_first | 0 | | Handler_read_key | 0 | | Handler_read_last | 0 | | Handler_read_next | 425 | | Handler_read_prev | 0 | | Handler_read_rnd | 0 | | Handler_read_rnd_next | 0 | ... | Handler_update | 0 | | Handler_write | 0 | +----------------------------+-------+ 16 rows in set (0.00 sec)
  120. 120. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 120 Newer Fulltext Optimizations (cont.)mysql-5.7.5 (osm) > EXPLAIN SELECT count(*) FROM way_tags WHERE MATCH(v) AGAINST('gloucester'); +----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+------------------------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+------------------------------+ | 1 | SIMPLE | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | Select tables optimized away | +----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+------------------------------+ 1 row in set, 1 warning (0.00 sec) mysql-5.7.5 (osm) > SHOW STATUS like 'Hand%'; +----------------------------+-------+ | Variable_name | Value | +----------------------------+-------+ | Handler_commit | 1 | | Handler_delete | 0 | ... | Handler_read_first | 0 | | Handler_read_key | 0 | | Handler_read_last | 0 | | Handler_read_next | 0 | | Handler_read_prev | 0 | | Handler_read_rnd | 0 | | Handler_read_rnd_next | 0 | ... | Handler_update | 0 | | Handler_write | 0 | +----------------------------+-------+ 18 rows in set (0.00 sec) It’s counting directly from the FULLTEXT index It’s counting directly from the FULLTEXT index
  121. 121. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 121 Open Issues and Limitations ● No postfix support (wildcards) ● Simple Ranking (and different from MyISAM) ● No stemming support ● Some multi-language limitations More on FULLTEXT InnoDB support: http://www.drdobbs.com/database/full-text-search-with-innodb/231902587
  122. 122. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 122 Alternatives ● Apache Lucene – Solr – Elasticsearch ● Sphinx – SphinxSE
  123. 123. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 123 JOINS Query Optimization: From 0 to 10 (and up to 5.7)
  124. 124. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 124 (Block) Nested Loop Join ● Until MySQL 5.5 there was only one algorithm to execute a JOIN: node_id version lat lon 1 1 52 0.5 1 2 52 0.5 2 1 51 1 3 1 53 1.5 node_id version k v 1 1 name Big Benn 1 1 tourism attraction 1 2 name Big Ben 1 2 tourism attraction 3 1 name London Eye
  125. 125. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 125 Extra Access type: eq_ref mysql-5.6.21 (osm) > EXPLAIN SELECT * FROM nodes JOIN node_tags USING(node_id, version) WHERE node_tags.v= 'Big Ben'G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: node_tags type: ref possible_keys: PRIMARY,v_idx key: v_idx key_len: 767 ref: const rows: 1 Extra: Using where; Using index *************************** 2. row *************************** id: 1 select_type: SIMPLE table: nodes type: eq_ref possible_keys: PRIMARY,version_idx key: PRIMARY key_len: 16 ref: osm.node_tags.node_id,osm.node_tags.version rows: 1 Extra: NULL 2 rows in set (0.00 sec) eq_ref is similar to ref, but allows faster JOINS because, by using a unique key, it only has to search one row for each previous result eq_ref is similar to ref, but allows faster JOINS because, by using a unique key, it only has to search one row for each previous result
  126. 126. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 126 JOIN Optimization ● Two main goals: – Perform an effective filtering on each table access, if possible using indexes – Perform the access in the most efficient table order ● When joining 3 or more tables in a star schema, the "covering index" strategy can have a huge impact
  127. 127. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 127 Example: optimize this JOIN (I) SELECT n.node_id, n.latitude, n.longitude FROM way_nodes w_n JOIN way_tags w_t ON w_n.way_id = w_t.way_id and w_n.version = w_t.version JOIN nodes n ON w_n.node_id = n.node_id JOIN node_tags n_t ON n.node_id = n_t.node_id and n.version = n_t.version WHERE w_t.k = 'building' and n_t.k = 'entrance' and n_t.v = 'main'; We start without secondary indexes We start without secondary indexes
  128. 128. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 128 Example: optimize this JOIN (II) ************************ 1. row ************************ id: 1 select_type: SIMPLE table: w_t type: index possible_keys: PRIMARY key: PRIMARY key_len: 783 ref: NULL rows: 1335702 Extra: Using where; Using index ************************ 2. row ************************ id: 1 select_type: SIMPLE table: w_n type: ref possible_keys: PRIMARY key: PRIMARY key_len: 16 ref: osm.w_t.way_id,osm.w_t.version rows: 3 Extra: NULL mysql-5.6.21 (osm) > SELECT … 858 rows in set (9.00 sec) ************************ 3. row ************************ id: 1 select_type: SIMPLE table: n_t type: ref possible_keys: PRIMARY key: PRIMARY key_len: 8 ref: osm.w_n.node_id rows: 1 Extra: Using where ************************ 4. row ************************ id: 1 select_type: SIMPLE table: n type: eq_ref possible_keys: PRIMARY key: PRIMARY key_len: 16 ref: osm.w_n.node_id,osm.n_t.version rows: 1 Extra: Using index 4 rows in set (0.01 sec)
  129. 129. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 129 Example: optimize this JOIN (III) mysql-5.6.21 (osm) > ALTER TABLE way_tags ADD INDEX k_idx(k); Query OK, 0 rows affected (4.80 sec) Records: 0 Duplicates: 0 Warnings: 0 Creating an index on way_tags.k Creating an index on way_tags.k
  130. 130. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 130 Example: optimize this JOIN (IV) ********************** 1. row ********************** id: 1 select_type: SIMPLE table: w_t type: ref possible_keys: PRIMARY,k_idx key: k_idx key_len: 767 ref: const rows: 452274 Extra: Using where; Using index ********************** 2. row ********************** id: 1 select_type: SIMPLE table: w_n type: ref possible_keys: PRIMARY key: PRIMARY key_len: 16 ref: osm.w_t.way_id,osm.w_t.version rows: 3 Extra: NULL mysql-5.6.21 (osm) > SELECT … 858 rows in set (8.58 sec) It seems like the index is not very useful It seems like the index is not very useful ********************** 3. row ********************** id: 1 select_type: SIMPLE table: n_t type: ref possible_keys: PRIMARY key: PRIMARY key_len: 8 ref: osm.w_n.node_id rows: 1 Extra: Using where ********************** 4. row ********************** id: 1 select_type: SIMPLE table: n type: eq_ref possible_keys: PRIMARY key: PRIMARY key_len: 16 ref: osm.w_n.node_id,osm.n_t.version rows: 1 Extra: NULL 4 rows in set (0.00 sec)
  131. 131. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 131 Example: optimize this JOIN (V) mysql-5.6.21 (osm) > ALTER TABLE node_tags ADD INDEX k_idx(k); Query OK, 0 rows affected (2.82 sec) Records: 0 Duplicates: 0 Warnings: 0 The order does not seem to be adequate, let's try adding an index to start by accessing node_tags The order does not seem to be adequate, let's try adding an index to start by accessing node_tags
  132. 132. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 132 Example: optimize this JOIN (VI) ********************** 1. row ********************** id: 1 select_type: SIMPLE table: w_t type: ref possible_keys: PRIMARY,k_idx key: k_idx key_len: 767 ref: const rows: 452274 Extra: Using where; Using index ********************** 2. row ********************** id: 1 select_type: SIMPLE table: w_n type: ref possible_keys: PRIMARY key: PRIMARY key_len: 16 ref: osm.w_t.way_id,osm.w_t.version rows: 3 Extra: NULL mysql-5.6.21 (osm) > SELECT … 858 rows in set (7.33 sec) ********************** 3. row ********************** id: 1 select_type: SIMPLE table: n_t type: ref possible_keys: PRIMARY,k_idx key: PRIMARY key_len: 8 ref: osm.w_n.node_id rows: 1 Extra: Using where ********************** 4. row ********************** id: 1 select_type: SIMPLE table: n type: eq_ref possible_keys: PRIMARY key: PRIMARY key_len: 16 ref: osm.w_n.node_id,osm.n_t.version rows: 1 Extra: NULL 4 rows in set (0.00 sec) It keeps using the wrong order, even if we delete the w_t.k_idx index It keeps using the wrong order, even if we delete the w_t.k_idx index
  133. 133. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 133 Example: optimize this JOIN (VII) SELECT STRAIGHT_JOIN n.node_id, n.latitude, n.longitude FROM node_tags n_t JOIN nodes n ON n.node_id = n_t.node_id and n.version = n_t.version JOIN way_nodes w_n ON w_n.node_id = n.node_id JOIN way_tags w_t ON w_n.way_id = w_t.way_id and w_n.version = w_t.version WHERE w_t.k = 'building' and n_t.k = 'entrance' and n_t.v = 'main'; Let's see why rewriting it into this query Let's see why rewriting it into this query
  134. 134. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 134 Example: optimize this JOIN (VIII) ********************** 1. row ********************** id: 1 select_type: SIMPLE table: n_t type: ref possible_keys: PRIMARY,k_idx key: k_idx key_len: 767 ref: const rows: 2390 Extra: Using index condition; Using where ********************** 2. row ********************** id: 1 select_type: SIMPLE table: n type: eq_ref possible_keys: PRIMARY key: PRIMARY key_len: 16 ref: osm.n_t.node_id,osm.n_t.version rows: 1 Extra: NULL There is no index on w_n that would allow efficient access There is no index on w_n that would allow efficient access ********************** 3. row ********************** id: 1 select_type: SIMPLE table: w_n type: ALL possible_keys: PRIMARY key: NULL key_len: NULL ref: NULL rows: 3597858 Extra: Using where; Using join buffer (Block Nested Loop) ********************** 4. row ********************** id: 1 select_type: SIMPLE table: w_t type: eq_ref possible_keys: PRIMARY key: PRIMARY key_len: 783 ref: osm.w_n.way_id,osm.w_n.version,const rows: 1 Extra: Using where; Using index 4 rows in set (0.00 sec)
  135. 135. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 135 Example: optimize this JOIN (IX) mysql-5.6.21 (osm) > ALTER TABLE way_nodes ADD INDEX node_id_idx(node_id); Query OK, 0 rows affected (17.77 sec) Records: 0 Duplicates: 0 Warnings: 0
  136. 136. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 136 Example: optimize this JOIN (X) ********************** 1. row ********************** id: 1 select_type: SIMPLE table: n_t type: ref possible_keys: PRIMARY,k_idx key: k_idx key_len: 767 ref: const rows: 2390 Extra: Using index condition; Using where ********************** 2. row ********************** id: 1 select_type: SIMPLE table: n type: eq_ref possible_keys: PRIMARY key: PRIMARY key_len: 16 ref: osm.n_t.node_id,osm.n_t.version rows: 1 Extra: NULL mysql-5.6.21 (osm) > SELECT … 858 rows in set (0.73 sec) Now it starts by the right table (without STRAIGHT_JOIN) Now it starts by the right table (without STRAIGHT_JOIN) ********************** 3. row ********************** id: 1 select_type: SIMPLE table: w_n type: ref possible_keys: PRIMARY,node_id_idx key: node_id_idx key_len: 8 ref: osm.n_t.node_id rows: 1 Extra: Using index ********************** 4. row ********************** id: 1 select_type: SIMPLE table: w_t type: eq_ref possible_keys: PRIMARY key: PRIMARY key_len: 783 ref: osm.w_n.way_id,osm.w_n.version,const rows: 1 Extra: Using where; Using index 4 rows in set (0.04 sec)
  137. 137. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 137 Example: optimize this JOIN (XI) ************************* 1. row ************************* id: 1 select_type: SIMPLE table: n_t type: ref possible_keys: PRIMARY,k_idx,k_v_idx key: k_v_idx key_len: 1534 ref: const,const rows: 900 Extra: Using where; Using index ************************* 2. row ************************* id: 1 select_type: SIMPLE table: n type: eq_ref possible_keys: PRIMARY key: PRIMARY key_len: 16 ref: osm.n_t.node_id,osm.n_t.version rows: 1 Extra: NULL mysql-5.6.21 (osm) > SELECT ... 858 rows in set (0.02 sec) An index on (k,v) is even better An index on (k,v) is even better ************************ 3. row ************************ id: 1 select_type: SIMPLE table: w_n type: ref possible_keys: PRIMARY,node_id_idx key: node_id_idx key_len: 8 ref: osm.n_t.node_id rows: 1 Extra: Using index ************************ 4. row ************************ id: 1 select_type: SIMPLE table: w_t type: eq_ref possible_keys: PRIMARY key: PRIMARY key_len: 783 ref: osm.w_n.way_id,osm.w_n.version,const rows: 1 Extra: Using where; Using index 4 rows in set (0.00 sec)
  138. 138. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 138 “New” JOIN methods ● MySQL 5.6 added: – Batch Key Access ● MariaDB has since 5.3: – Batch Key Access – Hash Joins – Slightly modified versions of the above ones (with “incremental” buffers to join 3 or more tables)
  139. 139. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 139 Multi-range read • This optimization orders results obtained from a secondary key in primary key/physical order before accessing the rows – It may help exection time of queries when disk-bound – It requires tunning of the read_rnd_buffer_size (size of the buffer used for ordering the results) • BKA JOINs are based on the mrr optimization
  140. 140. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 140 MRR Example (I) mysql-5.6.21 (osm) > EXPLAIN SELECT * FROM nodes WHERE timestamp >= '2013-07-01 00:00:00' AND timestamp < '2014-01-01 00:00:00'G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: nodes type: range possible_keys: nodes_timestamp_idx key: nodes_timestamp_idx key_len: 5 ref: NULL rows: 429684 Extra: Using index condition; Using MRR 1 row in set (0.02 sec)
  141. 141. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 141 MRR example (II) [restart] mysql> SET optimizer_switch='mrr=off'; mysql> SELECT * FROM nodes WHERE timestamp >= '2013-07-01 00:00:00' AND timestamp < '2014-01-01 00:00:00'; 205617 rows in set (5.16 sec) mysql> SELECT * FROM nodes WHERE timestamp >= '2013-07-01 00:00:00' AND timestamp < '2014-01-01 00:00:00'; 205617 rows in set (0.60 sec) [restart] mysql> SET read_rnd_buffer_size=50 * 1024 * 1024; mysql> SELECT * FROM nodes WHERE timestamp >= '2013-07-01 00:00:00' AND timestamp < '2014-01-01 00:00:00'; 205617 rows in set (2.39 sec) mysql> SELECT * FROM nodes WHERE timestamp >= '2013-07-01 00:00:00' AND timestamp < '2014-01-01 00:00:00'; 205617 rows in set (0.73 sec) “Cold” results are significantly better with mrr (but it can impact negatively, too) “Cold” results are significantly better with mrr (but it can impact negatively, too)
  142. 142. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 142 Batch Key Access node_id version lat lon 1 1 52 0.5 1 2 52 0.5 2 1 51 1 3 1 53 1.5 node_id version k v 1 1 name Big Benn 1 1 tourism attraction 1 2 name Big Ben 1 2 tourism attraction 3 1 amenity cafe Buffer sorted in physical/PK order
  143. 143. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 143 Hash Joins • Only work for equi-joins node_id version lat lon 1 1 52 0.5 1 2 52 0.5 2 1 51 1 3 1 53 1.5 node_id version k v 1 1 name Big Benn 1 1 tourism attraction 1 2 name Big Ben 1 2 tourism attraction 3 1 amenity cafe Hash table for faster access to rows
  144. 144. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 144 MySQL Configuration • BKA requires changes of default optimizer configuration: mysql-5.7.5 (osm) > SET optimizer_switch= 'mrr=on'; mysql-5.7.5 (osm) > SET optimizer_switch= 'mrr_cost_based=off'; mysql-5.7.5 (osm) > SET optimizer_switch= 'batch_key_access=on'; – Additionally, configuring the join_buffer_size adequately
  145. 145. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 145 MariaDB configuration mariadb-10.0.14 (osm) > SET optimizer_switch = 'join_cache_incremental=on'; mariadb-10.0.14 (osm) > SET optimizer_switch = 'join_cache_hashed=on'; mariadb-10.0.14 (osm) > SET optimizer_switch = 'join_cache_bka=on'; - Enabled by default mariadb-10.0.14 (osm) > SET join_cache_level = 3 (for hash joins) mariadb-10.0.14 (osm) > SET join_cache_level = 5 (for BKA) - Also, configure join_buffer_size appropriately. - Hash joins, like BKA, are highly dependent on disk-bound DBs to be effective due to the extra overhead
  146. 146. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 146 Nested Loop Join (cold buffers buffer_pool=100MB, join_buffer=4M) mariadb-10.0.14 (osm) > EXPLAIN SELECT changeset_id, count(*) FROM changesets JOIN nodes on changesets.id = nodes.changeset_id GROUP BY visibleG ******************** 1. row ******************** id: 1 select_type: SIMPLE table: changesets type: index possible_keys: PRIMARY key: PRIMARY key_len: 8 ref: NULL rows: 69115 Extra: Using index; Using temporary; Using filesort ******************** 2. row ******************** id: 1 select_type: SIMPLE table: nodes type: ref possible_keys: changeset_id key: changeset_id key_len: 8 ref: osm.changesets.id rows: 19 Extra: 2 rows in set (0.00 sec) mariadb-10.0.14 (osm) > SELECT visible, count(*) FROM changesets JOIN nodes on changesets.id = nodes.changeset_id GROUP BY visible; +---------+----------+ | visible | count(*) | +---------+----------+ | 1 | 2865312 | +---------+----------+ 1 row in set (32.86 sec)
  147. 147. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 147 Hash Join (cold buffers, buffer_pool=100M, join_buffer=4M) mariadb-10.0.14 (osm) > EXPLAIN SELECT changeset_id, count(*) FROM changesets JOIN nodes on changesets.id = nodes.changeset_id GROUP BY visibleG ******************** 1. row ******************** id: 1 select_type: SIMPLE table: changesets type: index possible_keys: PRIMARY key: PRIMARY key_len: 8 ref: NULL rows: 69115 Extra: Using index; Using temporary; Using filesort ******************** 2. row ******************** id: 1 select_type: SIMPLE table: nodes type: hash_ALL possible_keys: changeset_id key: #hash#changeset_id key_len: 8 ref: osm.changesets.id rows: 2781732 Extra: Using join buffer (flat, BNLH join) 2 rows in set (0.00 sec) mariadb-10.0.14 (osm) > SELECT visible, count(*) FROM changesets JOIN nodes on changesets.id = nodes.changeset_id GROUP BY visible; +---------+----------+ | visible | count(*) | +---------+----------+ | 1 | 2865312 | +---------+----------+ 1 row in set (6.66 sec)
  148. 148. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 148 SUBQUERIES Query Optimization: From 0 to 10 (and up to 5.7)
  149. 149. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 149 Access types: unique_subquery/index_subquery mysql-5.6.21 (osm) > EXPLAIN SELECT * FROM node_tags WHERE v = 'Big Ben' and node_id NOT IN (SELECT node_id FROM nodes WHERE tile < 100000000)G ************** 1. row ************** id: 1 select_type: PRIMARY table: node_tags type: ref possible_keys: v_idx key: v_idx key_len: 767 ref: const rows: 1 Extra: Using where; Using index Unique subquery is similar, but using a unique or primary key Unique subquery is similar, but using a unique or primary key ************** 2. row ************** id: 2 select_type: DEPENDENT SUBQUERY table: nodes type: index_subquery possible_keys: PRIMARY,nodes_tile_idx key: PRIMARY key_len: 8 ref: func rows: 1 Extra: Using where 2 rows in set (0.00 sec)
  150. 150. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 150 Subqueries in MySQL ● MySQL versions traditionally had very bad press regarding subquries – It was common to recommend rewriting them (when possible) into JOINS ● Since MySQL 5.6, its query execution plans have improved significantly
  151. 151. © 2014 Jaime Crespo. http://jynus.com. License: CC-BY-SA-4.0 Query Optimization: From 0 to 10 (and up to 5.7) 151 Lazy Materialization of derived tables ● Option available since MySQL 5.6 – Improves the execution time of EXPLAIN (it no longer needs to execute subqueries) – Derived tables can be indexed automatically at execution time to improve its performance

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