Webinar 2013 advanced_query_tuning

Ad

Ad

Ad

Ad

Ad

Ad

Ad

Ad

Ad

Ad

Ad

Ad

Advanced MySQL Query Tuning
Alexander Rubin
July 21, 2013

www.percona.com
About Me
•  Working with MySQL for over 10 years
–  Started at MySQL AB, then Sun Microsystems,
–  then Or...

www.percona.com
§  Indexes
– How B-tree works
– Range scans
§  Queries
– Temporary Tables and Filesort in MySQL
– GROUP ...

www.percona.com
How to Deal with Slow Performance
Indexes

www.percona.com
MySQL Index Types: B-Tree
•  When you add index (except for MEMORY)
MySQL will use B-Tree
•  Support equal...

www.percona.com
MySQL Index Types: B-Tree
•  Scan thru the tree and go directly to 1 leaf
•  Stop
Equality search: select ...

www.percona.com
MySQL Index Types: B-Tree
•  Scan thru the tree and visit many leafs/nodes
Range: select * from table wher...

www.percona.com
CREATE TABLE City (!
ID int(11) NOT NULL AUTO_INCREMENT,!
Name char(35) NOT NULL DEFAULT '',!
CountryCode ...

www.percona.com
• MySQL will use 1 (best) index
mysql> explain select * from City where ID = 1;!
+-------+-------+--------...

www.percona.com
•  Leftmost part of combined index
mysql> alter table City add key !
comb(CountryCode, District, Populatio...

www.percona.com
• Leftmost part of combined index
mysql> explain select * from City !
where CountryCode = 'USA'G!
********...

www.percona.com
•  Key_len = total size (in bytes) of index parts used
Index: comb(CountryCode, District, Population)!
!
!...

www.percona.com
• 2 Leftmost Fields
mysql> explain select * from City !
where CountryCode = 'USA' and District = 'Californ...

www.percona.com
• 3 Leftmost Fields
mysql> explain select * from City !
where CountryCode = 'USA' and District = 'Californ...

www.percona.com
• Can’t use combined index – not a leftmost part
mysql> explain select * from City where !
District = 'Cal...

www.percona.com
• Covered index = cover all fields in query
select name from City where CountryCode = 'USA'
and District =...

www.percona.com
• Explain
mysql> explain select name from City where CountryCode =
'USA' and District = 'Alaska' and popul...

www.percona.com
Order of Fields in Index
•  select * from City where district = 'California' and
population > 30000
•  Ind...

www.percona.com
Order of Fields in Index: Example
mysql> alter table City add key comb1(district, population);!
!
mysql> e...

www.percona.com
Order of Fields in Index: Example
mysql> alter table City add key comb2(population, district);!
!
mysql> e...

www.percona.com
Simplified BTree Scan Example I
Root
CA
10K –
15K
… …
100K-105K
… …
… … NC
Comb1(district,population)
1.  ...

www.percona.com
Simplified BTree Scan Example II
Root
10K –
15K
CA
…
NC
… …
100K
-105K
CA
…
NC
Comb1(population,district)
...

www.percona.com
Index Cardinality: Example
mysql> alter table City !
add key comb2(population, District);!
!
explain selec...

www.percona.com
How to Deal with Slow Performance
Queries

www.percona.com
Complex Slow Queries
The World’s Most Popular Open Source Database
… Group By …
… Order By …
Select distin...

www.percona.com
GROUP BY Queries

www.percona.com
mysql> explain select CountryCode, count(*) from City
group by CountryCodeG
id: 1
select_type: SIMPLE
tabl...

www.percona.com
Temporary Tables: Theory

www.percona.com
•  MySQL can create temporary tables when query uses:
•  GROUP BY
•  Range + ORDER BY
•  Some other expres...

www.percona.com
•  First, MySQL tries to create temporary table in memory
•  MySQL configuration variables:
•  tmp_table_s...

www.percona.com
MySQL
temp table
>
tmp_table_
size
OR
MySQL
temp table
>
max_heap_
table_size
convert to
MyISAM
temporary
...

www.percona.com
•  MEMORY engine does not support BLOB/TEXT
•  select blob_field from table group by field1
•  select conc...

www.percona.com
Temporary Tables: Practice

www.percona.com
6M rows, ~2G in size
CREATE TABLE ontime_2012 (
YearD int(11) DEFAULT NULL,
MonthD tinyint(4) DEFAULT NULL...

www.percona.com
SELECT max(DepDelayMinutes),
carrier, dayofweek
FROM ontime_2012
WHERE dayofweek = 7
GROUP BY Carrier
•  F...

www.percona.com
select max(DepDelayMinutes), carrier, dayofweek
from ontime_2012
where dayofweek = 7
group by Carrier
type...

www.percona.com
mysql> alter table ontime_2012 add key (dayofweek);
explain select max(DepDelayMinutes), Carrier,
dayofwee...

www.percona.com
mysql> alter table ontime_2012
add key covered(dayofweek, Carrier, DepDelayMinutes);
explain select max(De...

www.percona.com
mysql> explain select max(DepDelayMinutes), Carrier,
dayofweek from ontime_2012
where dayofweek > 3 group ...

www.percona.com
(select max(DepDelayMinutes), Carrier, dayofweek
from ontime_2012
where dayofweek = 3
group by Carrier, da...

www.percona.com
*************************** 1. row ***************************
table: ontime_2012
key: covered
...
Extra: ...

$www.percona.com GROUP BY: Loose index scan •  Loose index scan: •  considers only a fraction of the keys in an index •  Fo...$

www.percona.com
Loose index scan example
mysql> alter table ontime_2012 add key loose_index_scan
(Carrier, dayofweek, DepD...

www.percona.com
GROUP BY: Tight index scan
•  Full index scan or a range index scan
•  Can work if loose index scan can t ...

www.percona.com
Loose index scan vs. tight index scan
Table: ontime_2012, 6M rows, data: 2G, index: 210M
CREATE TABLE onti...

www.percona.com
Loose index scan vs. tight index scan
Loose index scan
select max(DepDelayMinutes) as ddm, Carrier, dayofw...

www.percona.com
Loose index scan vs. tight index scan
Loose index scan
select max(DepDelayMinutes) as ddm, Carrier, dayofw...

www.percona.com
Loose index scan vs. tight index scan
Loose index scan
select max(DepDelayMinutes) as ddm, Carrier, dayofw...

www.percona.com
Loose index scan vs. tight index scan
Temporary table
select max(DepDelayMinutes) as ddm, Carrier, dayofwe...

www.percona.com
Loose index scan vs. tight index scan
Tight Index Scan
select max(DepDelayMinutes) as ddm, Carrier, dayofw...

www.percona.com
Loose index scan vs. tight index scan
Results
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Loose index scan Tight Index...

www.percona.com
Where loose index scan is not supported
•  AVG() + Group By – loose index scan is not supported
mysql> exp...

www.percona.com
ORDER BY and filesort

www.percona.com
mysql> explain select district, name, population from City
where CountryCode = 'USA' order by population d...

www.percona.com
mysql> alter table City
add key my_sort2 (CountryCode, population);
mysql> explain select district, name, ...

www.percona.com
mysql> alter table ontime_2012 add key (DepDelayMinutes);
Query OK, 0 rows affected (38.68 sec)
mysql> exp...

www.percona.com
If Index points to the beginning of the table (physically) = fast
As it stops after 10 rows (LIMIT 10)

www.percona.com
If Index points to the end of table (physically) or random = slower
Much more rows to scan (and skip)

www.percona.com
Example: Social Graph

www.percona.com
https://blog.twitter.com/2010/introducing-flockdb
•  Source_id = <YOU>
•  Destination_id = IDs of people f...

www.percona.com
CREATE TABLE social_graph (
source_id bigint(20) unsigned NOT NULL,
destination_id bigint(20) unsigned NOT...

www.percona.com
mysql> explain select * from social_graph where source_id = 927
and state in (0) order by position desc li...

www.percona.com
mysql> alter table social_graph add key
src_state_position(source_id, state, position);
mysql> select * fr...

www.percona.com
mysql> explain select * from social_graph where
source_id = 927 and state in (0) order by position
desc li...

www.percona.com
mysql> explain select * from where source_id = 927
and state in (0,2) order by position desc limit 100G
se...

www.percona.com
mysql> alter table social_graph
add key src_position(source_id, position);
mysql> explain select * from so...

www.percona.com
mysql> explain select * from social_graph where
source_id = 927 and state in (1,2) order by position
desc ...

www.percona.com
mysql> explain select * from social_graph
ignore index (src_state_position)
where source_id = 927 and stat...

www.percona.com
Questions?
Thank you!

Share Slideshare

LinkedIn
Facebook
Twitter

Embed

Size (px)

Show related Slideshows at end

WordPress Shortcode

Link

Share
Email

MySQL Performance Tuning: Top 10 Tips by OSSCube 55797 views
MySQL Webinar 2/4 Performance tunin... by Mark Swarbrick 1044 views
Join-fu: The Art of SQL Tuning for ... by ZendCon 11241 views
Performance Tuning by Ligaya Turmelle 1437 views
浅析My sql事务隔离级别与锁 seanlook by 晓周 446 views
MySQL Performance Tips & Best Pract... by Isaac Mosquera 11710 views

View on Slideshare

1 of 69 Ad

View on Slideshare

1 of 69 Ad