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Top 10 tips for Oracle performance (Updated April 2015)


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Presentation given at IOUG Collaborate 2015 (and in other versions in the past)

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Top 10 tips for Oracle performance (Updated April 2015)

  1. 1. REMINDER Check in on the COLLABORATE mobile app Top 10 Oracle database tuning tips Guy Harrison, Executive Director, Information Mgt R&D, Dell Software Group Session ID#: 442 @guyharrison
  2. 2. Top 10 Oracle database tuning tips Guy Harrison, Executive Director, Information Mgt R&D, Dell Software Group
  3. 3. Dell Software Group3 Web: Email: Twitter: @guyharrison Introductions
  4. 4. 4 Dell Software Group
  5. 5. 5 Dell Software Group
  6. 6. 6 Dell Software Group
  7. 7. 7 Dell Software Group Dell and Quest – a brief history
  8. 8. Dell Software Group8 But Seriously
  9. 9. Dell Software Group9 The top 10 Be methodical and empirical Optimize your database design Index Wisely Write efficient code Optimize the optimizer Tune SQL and PL/SQL Monitor and Manage contention Optimize memory to reduce IO Tune IO last, but TUNE it well
  10. 10. Dell - Restricted - Confidential Be methodical and empirical
  11. 11. Dell Software Group11 Hint 1: Methodical and Empirical tuning Methodical: • Have a plan • Focus on root causes, not symptoms • Hypothesis and experiment, not trial and error Empirical • Measure performance • Compare before and after • What is your control group? • Beware of “old DBA tales” and “silver bullets”
  12. 12. Dell Software Group12 Hint 1: Methodical and Empirical tuning Performance Troubleshooting • Identify the element of your workload which is contributing most to service time • Workload could be SQL or logical transaction • Element is typically CPU time + Oracle wait time • Find a way to reduce that element Tuning by layers • As above, but prioritize higher layers of the stack (which have flow on effects into lower layers) • Distinguish between symptoms and causes
  13. 13. Dell Software Group13 Basics of a database request
  14. 14. Dell Software Group14 The 4 layers in database performance
  15. 15. Dell Software Group15 What’s wrong with the donkey?
  16. 16. Dell Software Group16 Measurement • Standard SQL views • AWR reports • DB control/Cloud control • Toad/Spotlight other 3rd party tools • A single query can tell you a lot mples/Ch03/timeModelSimple. sql
  17. 17. Dell - Restricted - Confidential Database design
  18. 18. Dell Software Group18 Database design Third Normal form (3NF) • The key, the whole key and nothing but the key • OR – Don’t repeat yourself (DRY) 3NF discretion • Datatypes (VARCHARs vs LOBS, etc) • Subtypes • NULLS Denormalization • Replicate column values to avoid joins • Summary tables and materialized views • Vertical partitioning
  19. 19. Dell Software Group19 3NF is mostly Don’t Repeat Yourself (DRY) • We don’t want to repeat the student name every time they take a new test • We don’t want to repeat the test_name for every student that takes it • We don’t want the “repeating group” of answers – Also, we might not know how many questions there will be in future tests
  20. 20. Dell Software Group20 3NF version • Students take tests • Tests have questions • Students taking tests provide answers
  21. 21. Dell Software Group21 Don’t go to far! • In this example the designer pulled address into a separate table and city, country into another table. • It’s correct in theory, but it means that every time we want an employees address we have to join three tables. • It would have been better to have just one table
  22. 22. Dell Software Group22 Logical to Physical: Subtypes “Customers are people too”
  23. 23. Dell Software Group23 Subtypes • It’s usually better to put all the data in one table, or have two tables for each subtype • Having a “supertype” table and two “subtype” tables means you always have to join tables Probably don’t want to do this
  24. 24. Dell Software Group24 Denormalization
  25. 25. Dell - Restricted - Confidential Index Wisely
  26. 26. Dell Software Group26 Indexes • Choosing the best set of indexes is crucial • Create the best set of Concatenated (multi-column) indexes that will support your queries. • Indexes slow down transactions, so don’t create too many Indexes exist mainly to improve performance • You use the index when you want to look up one thing or a few things • You don’t use the index to read the whole book or read a whole chapter • You do use an index when you want to go to a specific page Think of indexes on a table like indexes in a book
  27. 27. Dell Software Group27 Concatenated index effectiveness • The more columns in the index the less IO it takes to resolve a query using all the columns • The order of the columns affects how the index can be used • If the index has all the columns, don’t need to touch the table at all SELECT cust_id FROM sh.customers c WHERE cust_first_name = 'Connor' AND cust_last_name = 'Bishop' AND cust_year_of_birth = 1976; 0 500 1000 1500 None last name last+first name last,first,BirthYear last,first,birthyear,id 1459 63 6 4 3 Logical IO
  28. 28. Dell Software Group28 Index overhead • Indexes speed up queries, but make DML (insert, update, Delete) slower • This chart shows how inserts slow down as more and more indexes are added • Deleting a row with lot’s of indexes is particularly expensive 0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000 1 (PK only) 2 3 4 5 6 7 1,191 6,671 8,691 10,719 12,727 14,285 16,316 Logical reads required Numberofindexes
  29. 29. Dell Software Group29 1 10 100 1000 0 10 20 30 40 50 60 70 80 90 100 ElaspedTime(s) Pct of table accessed Full Scan no caching Index sorted data, no caching Index unsorted, cached data Full Table scan, cached data Index or FTS? Break even points
  30. 30. Dell - Restricted - Confidential Application code
  31. 31. Dell Software Group31 Database coding guidelines SQL Execution • Don’t call the database unless you have to – cache data instead. • Reduce “hard” parsing by using bind variables Transaction design • Minimize lock duration using optimistic and Pessimistic locking strategies Network overhead • Array fetch and Insert • Stored procedures
  32. 32. Dell Software Group32 Parse overhead • It’s easy enough in most programming languages to create a new SQL every time you execute the query:
  33. 33. Dell Software Group33 Better to use the same SQL with different arguments: • Prepare the statement once, then execute many times with different arguments • Using bind variables
  34. 34. Dell Software Group34 Reduction in parse (SQL Compile) time 1,000 executions of the code on preceding two slides in Oracle 0 200 400 600 800 1000 1200 1400 No Bind variables Bind Variables Parse Time Other
  35. 35. Dell Software Group35 Designing transactions • There are two ways to design transaction locking • Pessimistic works best if you think someone else is going to “grab” your row before you’re finished • Optimistic works best if you thing no one else will “grab” the row Durationoflock Durationoflock
  36. 36. Dell Software Group36 Reduce Network traffic • “Round trips” to the database can add a lot of overhead • Two ways to reduce round trips: – Use the “Array” interface in your program code – Use stored procedures for complex interactions with the database
  37. 37. Dell Software Group37 Array fetch performance 0 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000 0 20 40 60 80 100 120 140 Array fetch size Logical Reads Network round trips
  38. 38. Dell Software Group38 Network – stored procedures • A stored procedure is code stored in the database • If you have a transaction that goes “back and forth” to the database, consider a stored procedure • ESPECIALLY if you are working across a slow network
  39. 39. Dell - Restricted - Confidential Optimize the optimizer
  40. 40. Dell Software Group40 Object Statistics Cardinality Estimates IO and CPU Estimates DB parameters And config Cost estimateSystem Statistics Table and index Structure Optimizer inputs • Remember: Garbage In : Garbage Out • The optimizer can only do a good job if statistics are up to date
  41. 41. Dell Software Group41 Histograms • Indexes are only good for getting small amounts of the table • So it might be a good idea to use an index to get “New Zealand” customers, but not “United States” • A histogram allows the optimizer to understand how the data is distributed and make the best decision • Create histograms to correct bad plans on skewed tables 0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000 20,000 SaudiArabia SouthAfrica Turkey NewZealand Denmark Argentina Singapore Japan Poland China Australia Brazil Canada Spain France UnitedKingdom Italy Germany UnitedStatesofAmerica Numberofrows
  42. 42. Dell Software Group42 Without a histogram Number of rows the estimated Real number of rows Optimizer chooses not to use an index
  43. 43. Dell Software Group43 With a histogram Optimizer estimate is correct Optimizer chooses to use an index
  44. 44. Dell Software Group44 DBMS_STATS GATHER_INDEX_STATS , GATHER_SCHEMA_STATS, GATHER_TABLE_STATS Basic statistics method_opt => 'FOR ALL INDEXED COLUMNS SIZE AUTO' Histograms method_opt => 'FOR ALL COLUMNS FOR COLUMNS (col1, col2)' Multi-column extended statistics method_opt => 'FOR ALL COLUMNS FOR COLUMNS (function(column)))' Expression extended statistics DBMS_STATS.gather_system_stats ( gathering_mode => 'NOWORKLOAD'); Non-workload system statistics DBMS_STATS.gather_system_stats (gathering_mode => 'INTERVAL', interval => 60); Workload system statistics
  45. 45. Dell - Restricted - Confidential Tune SQL and PL/SQL
  46. 46. Dell Software Group46 Find them and tune them Find SQL • Mine V$SQL • ASH, AWR tables • Database control, grid/cloud control • Toad, Spotlight Tune SQL • SQL Profiles • SQL Baselines • Rewrites • Hints (be careful) • SQL Optimizer
  47. 47. Dell Software Group47 V$SQL is your friend • Also, V$SQL_PLAN, V$SQL_PLAN_STATISTICS • Tkprof, session trace
  48. 48. Dell Software Group48
  49. 49. Dell Software Group49 Now let’s look at the donkey
  50. 50. Dell - Restricted - Confidential Monitor and manage contention
  51. 51. Dell Software Group51 Contention – the proverbial bottleneck Application Demand for DB services Contention for limited or serialized resources causes waits and or queuing Apparent demand at lower layers is reduced
  52. 52. Dell Software Group52 Types of contention Locks Usually locking problems are due to application locks (remember optimistic locking)? Sometimes internal locks can cause problems. Latches and Mutex Latches are very light weight locks that protect memory instead of tables Buffer contention When sessions have to wait for a memory “buffer” to become available
  53. 53. Dell Software Group53 Latches and mutex contention • Latches are like locks, but instead of protecting table rows, they protect memory (buffers) • If two sessions try to access the same area of memory, then one will wait • Instead of “sleeping” (like a lock) they waiting session will “spin” on the CPU for a very short time • Latch problems may indicate “hot” blocks • They might cause CPU drain (because of spinning) Buffers Database files user user user
  54. 54. Dell Software Group54 Database files Buffers Database Writer User Buffer Waits Write dirty blocks to disk Write to buffers Read from disk Read from buffers Free buffer waits • Database buffers improve performance by caching data in memory • When buffers are modified they are called “dirty” – DBWR writes to disk • When all the blocks are “dirty” then sessions have to wait for the buffers to be written before new data can be read • This might mean that your DBWR can’t write to disk fast enough
  55. 55. Dell Software Group55 Specific contention scenarios Lock/Latch Possible cause Library cache mutex Hard parsing no bind variables. Try CURSOR_SHARING=SIMILAR Library cache pin PL/SQL package parsing and invalidations Shared pool latch Hard parsing and possibly excessive SGA resizing Cache buffers chains Hot blocks, very high logical read rates Free Buffer waits DBWR failing to “keep up” with block changes Flashback buf free Insufficient IO bandwidth for flashback area Buffer busy Hot blocks – partitioning might help
  56. 56. Dell - Restricted - Confidential Optimize memory to reduce IO
  57. 57. Dell Software Group57 Memory is primarily used to avoid IO • Buffer cache avoids IO to table/index tablespaces • PGA avoids IO to temporary tablespace Buffer pools Program Global Area (PGA) Sort area Hash Area Data (USER) tablespace Temporary tablespace Oracle Session
  58. 58. Dell Software Group58 Temp tablespace IO can easily overwhelm table/index IO Time Available Memory Table/Index IO CPU Time Temp Segment IO Less MemoryMore Memory Memory Sort Single Pass Disk Sort Multi-pass Disk Sort
  59. 59. Dell Software Group59 Automatic Memory Management • Introduced in 11g, AMM manages allocations between and within PGA and SGA
  60. 60. Dell Software Group60 AMM can (rarely?) lead to thrashing or starvation • ALWAYS set minimum values for key components of the SGA
  61. 61. Dell - Restricted - Confidential Tune IO last, but tune it well
  62. 62. Dell Software Group62 IO Tuning • Disk IO is the slowest part of the database system, so it’s critical to performance • FIRST: – Tune SQL and application – Remove contention – Allocate memory • Only when you’ve done that will your IO demand be realistic. Then you can tune your IO
  63. 63. Dell Software Group63 Basics of IO tuning (magnetic disks) • The amount of IO you can support depends on the number of disks you have • Provide enough disks to support the amount of IO you need • even if that means the disks are not filled with data • Magnetics disks can do between 75-150 IO per second (IOPS) – do the math! 0 20 40 60 80 100 120 140 160 180 200 SATA 7,200 rpm SATA 10,000 rpm SAS 10,000 rpm SAS 15,000 rpm IO/ps
  64. 64. Dell Software Group64 Disk Drive latency • Latency is the time taken to perform a single IO • Most disk drives can return an IO in 5-10 ms – Faster if the disk has a memory cache • Disk latency increases with: – Throughput (best at 50-75% of maximum) – Disk fill (best at 50% capacity) • To get best performance disks should be – Sparsely populated – Under only moderate load • RAID 0+1 is the preferred configuration 0 10 20 30 40 50 60 70 80 90 100 0 100 200 300 400 500 ResponseTime(ms) IO/second
  65. 65. Dell Software Group65 The more that things change....
  66. 66. Dell Software Group66 Disks are not getting faster
  67. 67. Dell Software Group67 SSD - Cheaper by the IO 4,000 80 25 15 0 1,000 2,000 3,000 4,000 5,000 Magnetic Disk SSD SATA Flash SSD PCI flash SSD DDR-RAM Seek time (us)
  68. 68. Dell Software Group68 But not by the GB 0.35 0.28 0.21 0.17 0.13 2.9 2.2 1.7 1.3 1 10 7.4 5.3 3.2 2.3 0 2 4 6 8 10 12 2011 2012 2013 2014 2015 $$/GB HDD MLC SDD SLC SSD 0.35 0.28 0.21 0.17 0.13 2.9 2.2 1.7 1.3 1 2.3 0.1 1 10 2011 2012 2013 2014 2015 $$/GB HDD MLC SDD SLC SSD
  69. 69. Dell Software Group69 Tiered storage management Main Memory DDR SSD Flash SSD Fast Disk (SAS, RAID 0+1) Slow Disk (SATA, RAID 5) Tape, Flat Files, Hadoop $/IOP $/GB
  70. 70. Dell Software Group70 Random reads – FusionIO 2,211 583 121 0 500 1000 1500 2000 2500 SAS disk, no flash cache SAS disk, flash cache Table on SSD Elapsed time (s) CPU Other DB File IO Flash cache IO
  71. 71. Dell Software Group71 Full table scans Flash cache doesn’t accelerate Full table scans b/c scans use direct path reads and flash cache only accelerates buffered reads 418 398 72 0 100 200 300 400 500 SAS disk, no flash cache SAS disk, flash cache Table on SSD Elasped time (s) CPU Other DB File IO Flash Cache IO
  72. 72. Dell Software Group72 Disk Sorts – temp tablespace SSD vs HDD 0 500 1000 1500 2000 2500 3000 3500 4000 050100150200250300 Elapsedtime(s) Sort Area Size SAS based TTS SSD based TTS Single Pass Disk Sort Multi-pass Disk Sort
  73. 73. Dell Software Group73 Concurrent redo workload (x10) 1,605 1,637 397 331 1,944 1,681 0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 SAS based redo log Flash based redo log Elapsed time (s) CPU Other Log File IO
  74. 74. Dell - Restricted - Confidential Tune RAC
  75. 75. Dell Software Group75 RAC will scale well, providing that…. a) The time taken to transfer a block across the interconnect is much less than the time taken to read from disk Load is reasonably well balanced across the instances in the cluster The overhead of maintaining cluster consistency does not dominate overall response time
  76. 76. Dell Software Group76 Toad: your companion in the Big Data revolution
  77. 77. Dell Software Group77 Dell In-Memory Appliances for Cloudera Enterprise Mid-Size Configuration 16 Node Cluster R720- 4 Infrastructure Nodes R720XD- 12 Data Nodes Force10- S4810P Force10- S55 ~528TB (disk raw space) ~4.5 TB (raw memory) Starter Configuration 8 Node Cluster R720- 4 Infrastructure Nodes R720XD- 4 Data Nodes Force10- S55 ~176TB (disk raw space) ~1.5TB (raw memory) Small Enterprise Configuration 24 Node Cluster R720- 4 Infrastructure Nodes R720XD- 20 Data Nodes ~880TB (disk raw space) ~7.5 TB (raw memory) Expansion Unit- R720XD-4 Data, Cloudera Enterprise Data Hub, Scale in Blocks
  78. 78. Dell Software Group78 Dell appliances for any database • Dell provides appliances and reference architectures specifically designed for: – Oracle – SQL Server – HANA – SSD database acceleration – Large memory footprints
  79. 79. 79 Dell Software Group Thank you.
  80. 80. Please complete the session evaluation We appreciate your feedback and insight You may complete the session evaluation either on paper or online via the mobile app