10 things you might not know about mysql

10 things you might not know about MySQLJorge Bernal <[email protected]>

Version 0.1

mailto:[email protected]

mailto:[email protected]

1Query cache

Beforemysql> SELECT AVG(Population) FROM City_huge;+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+| AVG(Population) |+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+| 354359.9948 | +‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+1 row in set (0.58 sec)

mysql> SELECT AVG(Population) FROM City_huge;+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+| AVG(Population) |+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+| 354359.9948 | +‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+1 row in set (0.56 sec)

Aftermysql> SELECT AVG(Population) FROM City_huge;+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+| AVG(Population) |+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+| 354359.9948 | +‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+1 row in set (0.56 sec)

mysql> SELECT AVG(Population) FROM City_huge;+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+| AVG(Population) |+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+| 354359.9948 | +‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+1 row in set (0.00 sec)

The magicSET global query_cache_size=8 * 1024 * 1024;mysql> SHOW GLOBAL VARIABLES LIKE 'query_cache%';+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐+| Variable_name | Value |+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐+| query_cache_limit | 1048576 | | query_cache_min_res_unit | 4096 | | query_cache_size | 8388608 | | query_cache_type | ON | | query_cache_wlock_invalidate | OFF | +‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐+5 rows in set (0.00 sec)

mysql> SHOW GLOBAL STATUS LIKE 'Qc%';+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐+| Variable_name | Value |+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐+| Qcache_free_blocks | 1 | | Qcache_free_memory | 8378312 | | Qcache_hits | 1 | | Qcache_inserts | 1 | | Qcache_lowmem_prunes | 0 | | Qcache_not_cached | 0 | | Qcache_queries_in_cache | 1 | | Qcache_total_blocks | 4 | +‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐+8 rows in set (0.00 sec)

2Life beyond MyISAM/

InnoDB

ARCHIVE MyISAM

80% compression

But...

• Only INSERT and SELECT

• No indexing

CSVmysql> ALTER TABLE City ENGINE=CSV;Query OK, 0 rows affected (0.05 sec)Records: 0 Duplicates: 0 Warnings: 0

root@warhol:/usr/local/mysql/data/world$ head City.CSV 1,"Kabul","AFG","Kabol",17800002,"Qandahar","AFG","Qandahar",2375003,"Herat","AFG","Herat",1868004,"Mazar‐e‐Sharif","AFG","Balkh",1278005,"Amsterdam","NLD","Noord‐Holland",7312006,"Rotterdam","NLD","Zuid‐Holland",5933217,"Haag","NLD","Zuid‐Holland",4409008,"Utrecht","NLD","Utrecht",2343239,"Eindhoven","NLD","Noord‐Brabant",20184310,"Tilburg","NLD","Noord‐Brabant",193238

Mergemysql> SHOW CREATE TABLE allweek\G[...]Create Table: CREATE TABLE `allweek` ( `ID` int(11) NOT NULL DEFAULT '0', `Name` char(35) NOT NULL DEFAULT '', `CountryCode` char(3) NOT NULL DEFAULT '', `District` char(20) NOT NULL DEFAULT '', `Population` int(11) NOT NULL DEFAULT '0', `modtime` datetime DEFAULT NULL, KEY `modtime` (`modtime`)) ENGINE=MRG_MyISAM DEFAULT CHARSET=latin1 UNION=(`monday`,`tuesday`,`wednesday`,`thursday`,`citydate`)1 row in set (0.00 sec)

3AUTO_INCREMENT

woes

mysql> CREATE TABLE t ( ‐> id INT NOT NULL PRIMARY KEY AUTO_INCREMENT ‐> );Query OK, 0 rows affected (0.00 sec)

mysql> INSERT INTO t (id) ‐> VALUES (NULL);Query OK, 1 row affected (0.04 sec)

mysql> SELECT * ‐> FROM t ‐> WHERE id IS NULL;+‐‐‐‐+| id |+‐‐‐‐+| 1 | +‐‐‐‐+

But...• id is AUTO_INCREMENT, so it’s 1

• let’s run that again



mysql> SELECT * ‐> FROM t ‐> WHERE id IS NULL;+‐‐‐‐+| id |+‐‐‐‐+| 1 | +‐‐‐‐+



mysql> SELECT * ‐> FROM t ‐> WHERE id IS NULL;+‐‐‐‐+| id |+‐‐‐‐+| 1 | +‐‐‐‐+mysql> SELECT * ‐> FROM t ‐> WHERE id IS NULL;Empty set (0.00 sec)

mysql> SELECT * FROM t;+‐‐‐‐+| id |+‐‐‐‐+| 1 | +‐‐‐‐+1 row in set (0.00 sec)

WTF???

• WHERE ID IS NULL acts as

WHERE ID = LAST_ISERT_ID()

• But only the first time

• Brought to you by some weird ODBC compatibility decision

4How to get random

data

SELECT name FROM randomORDER BY RAND()LIMIT 1

SELECT name FROM randomORDER BY RAND()LIMIT 1X

Wrong!

There is a better waySELECT nameFROM random JOIN( SELECT CEIL( RAND() * (SELECT MAX(id) FROM random)) AS id) AS r2USING (id);

Really?

Really?

0,10

1,00

10,00

100,00

1.000,00

10.000,00

100 1000 10000 100000

Seco

nds

Table Size

ORDER BY RAND() Subquery

So...

Every time you use ORDER BY RAND()...God kills a kitten

Please, think of the kittens

5Prefix indexes

There’s no need to index the whole

column

Name is CHAR(52)mysql> SHOW CREATE TABLE Country\G*************************** 1. row *************************** Table: CountryCreate Table: CREATE TABLE `Country` ( `Code` char(3) NOT NULL DEFAULT '', `Name` char(52) NOT NULL DEFAULT '', `Continent` enum('Asia','Europe','North America','Africa','Oceania','Antarctica','South America') NOT NULL DEFAULT 'Asia', `Region` char(26) NOT NULL DEFAULT '', `SurfaceArea` float(10,2) NOT NULL DEFAULT '0.00', `IndepYear` smallint(6) DEFAULT NULL, `Population` int(11) NOT NULL DEFAULT '0', `LifeExpectancy` float(3,1) DEFAULT NULL, `GNP` float(10,2) DEFAULT NULL, `GNPOld` float(10,2) DEFAULT NULL, `LocalName` char(45) NOT NULL DEFAULT '', `GovernmentForm` char(45) NOT NULL DEFAULT '', `HeadOfState` char(60) DEFAULT NULL, `Capital` int(11) DEFAULT NULL, `Code2` char(2) NOT NULL DEFAULT '', PRIMARY KEY (`Code`)) ENGINE=MyISAM DEFAULT CHARSET=latin11 row in set (0.02 sec)

mysql> SELECT COUNT(*) AS Total, COUNT(DISTINCT Name) AS Diff, COUNT(*) ‐ COUNT(DISTINCT Name) AS Dupes FROM Country;+‐‐‐‐‐‐‐+‐‐‐‐‐‐+‐‐‐‐‐‐‐+| Total | Diff | Dupes |+‐‐‐‐‐‐‐+‐‐‐‐‐‐+‐‐‐‐‐‐‐+| 239 | 239 | 0 | +‐‐‐‐‐‐‐+‐‐‐‐‐‐+‐‐‐‐‐‐‐+1 row in set (1.04 sec)mysql> SELECT COUNT(*) AS Total, COUNT(DISTINCT LEFT(Name,50)) AS Diff, COUNT(*) ‐ COUNT(DISTINCT LEFT(Name,50)) AS Dupes FROM Country;+‐‐‐‐‐‐‐+‐‐‐‐‐‐+‐‐‐‐‐‐‐+| Total | Diff | Dupes |+‐‐‐‐‐‐‐+‐‐‐‐‐‐+‐‐‐‐‐‐‐+| 239 | 239 | 0 | +‐‐‐‐‐‐‐+‐‐‐‐‐‐+‐‐‐‐‐‐‐+1 row in set (2.02 sec)

mysql> SELECT COUNT(*) AS Total, COUNT(DISTINCT LEFT(Name,20)) AS Diff, COUNT(*) ‐ COUNT(DISTINCT LEFT(Name,20)) AS Dupes FROM Country;+‐‐‐‐‐‐‐+‐‐‐‐‐‐+‐‐‐‐‐‐‐+| Total | Diff | Dupes |+‐‐‐‐‐‐‐+‐‐‐‐‐‐+‐‐‐‐‐‐‐+| 239 | 239 | 0 | +‐‐‐‐‐‐‐+‐‐‐‐‐‐+‐‐‐‐‐‐‐+1 row in set (0.93 sec)

mysql> SELECT COUNT(*) AS Total, COUNT(DISTINCT Name) AS Diff, COUNT(*) ‐ COUNT(DISTINCT Name) AS Dupes FROM Country;+‐‐‐‐‐‐‐+‐‐‐‐‐‐+‐‐‐‐‐‐‐+| Total | Diff | Dupes |+‐‐‐‐‐‐‐+‐‐‐‐‐‐+‐‐‐‐‐‐‐+| 239 | 239 | 0 | +‐‐‐‐‐‐‐+‐‐‐‐‐‐+‐‐‐‐‐‐‐+1 row in set (1.04 sec)mysql> SELECT COUNT(*) AS Total, COUNT(DISTINCT LEFT(Name,50)) AS Diff, COUNT(*) ‐ COUNT(DISTINCT LEFT(Name,50)) AS Dupes FROM Country;+‐‐‐‐‐‐‐+‐‐‐‐‐‐+‐‐‐‐‐‐‐+| Total | Diff | Dupes |+‐‐‐‐‐‐‐+‐‐‐‐‐‐+‐‐‐‐‐‐‐+| 239 | 239 | 0 | +‐‐‐‐‐‐‐+‐‐‐‐‐‐+‐‐‐‐‐‐‐+1 row in set (2.02 sec)


Got it? Cool! Now...

There is a better wayCREATE DEFINER=`root`@`localhost` PROCEDURE `pref_index`(t_name CHAR(255), c_name CHAR(255))BEGIN

DECLARE plength INT DEFAULT 1;SET @q = CONCAT('SELECT CHARACTER_MAXIMUM_LENGTH INTO @maxlen FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_SCHEMA = "world2" AND TABLE_NAME = "', t_name,'" AND COLUMN_NAME = "', c_name, '"');PREPARE q FROM @q;EXECUTE q;DEALLOCATE PREPARE q;

REPEAT SET @qq = CONCAT('SELECT COUNT(*) ‐ COUNT(DISTINCT ',c_name,') into @dupe FROM ',t_name); SET @pq = CONCAT('SELECT COUNT(*) ‐ COUNT(DISTINCT LEFT(',c_name,',',plength,')) into @pdupe FROM ',t_name);

PREPARE qs FROM @qq; EXECUTE qs; DEALLOCATE PREPARE qs;

PREPARE ps FROM @pq; EXECUTE ps; DEALLOCATE PREPARE ps;

SET plength = plength + 1;UNTIL plength >= @maxlen OR @pdupe = @dupeEND REPEAT;SELECT plength, @pdupe, @dupe;END

mysql> CALL pref_index('Country', 'Name');+‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐+| plength | @pdupe | @dupe |+‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐+| 18 | 0 | 0 | +‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐+1 row in set (1.18 sec)

Query OK, 0 rows affected (1.18 sec)


mysql> ALTER TABLE Country ADD KEY (Name(18));Query OK, 239 rows affected (1.48 sec)Records: 239 Duplicates: 0 Warnings: 0

mysql> CALL pref_index('Country', 'Name');+‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐+| plength | @pdupe | @dupe |+‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐+| 18 | 0 | 0 | +‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐+1 row in set (1.18 sec)

Query OK, 0 rows affected (1.18 sec)


mysql> ALTER TABLE Country ADD KEY (Name(18));Query OK, 239 rows affected (1.48 sec)Records: 239 Duplicates: 0 Warnings: 0

We just saved 34 bytes per row!

6InnoDB clustered index

Primary key

Leaf nodes

Index

Data stored in PK order

Indexes point to PK instead of actual data

So what?

Choose your PK wisely

Load data in ordermysql> load data infile '/tmp/city_order.txt' into table City_huge;Query OK, 818027 rows affected (15.86 sec)Records: 818027 Deleted: 0 Skipped: 0 Warnings: 0

mysql> load data infile '/tmp/city_rand.txt' into table City_huge;Query OK, 818027 rows affected (33 min 23.57 sec)Records: 818027 Deleted: 0 Skipped: 0 Warnings: 0

7Profiling

mysql> select * from v_client_portfolio_high;+‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+| client_id | client_first_name | client_last_name | portfolio_value |+‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+| 5 | ABNER | ROSSELLETT | 1252115.50 || 500 | CANDICE | BARTLETT | 1384877.50 |+‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+2 rows in set (4.01 sec)

mysql> select * from v_client_portfolio_high;+‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+| client_id | client_first_name | client_last_name | portfolio_value |+‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+| 5 | ABNER | ROSSELLETT | 1252115.50 || 500 | CANDICE | BARTLETT | 1384877.50 |+‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+2 rows in set (4.01 sec) Why?

mysql> set profiling=1;Query OK, 0 rows affected (0.00 sec)

mysql> select * from v_client_portfolio_high;+‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+| client_id | client_first_name | client_last_name | portfolio_value |+‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+| 5 | ABNER | ROSSELLETT | 1252115.50 || 500 | CANDICE | BARTLETT | 1384877.50 |+‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+2 rows in set (4.01 sec)

mysql> show profiles;+‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+| Query_ID | Duration | Query |+‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+| 1 | 0.00007600 | set profiling=1 || 2 | 4.01965600 | select * from v_client_portfolio_high |+‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+

mysql> select min(seq) seq,state,count(*) numb_ops, ‐> round(sum(duration),5) sum_dur, round(avg(duration),5) avg_dur, ‐> round(sum(cpu_user),5) sum_cpu, round(avg(cpu_user),5) avg_cpu ‐> from information_schema.profiling ‐> where query_id = 2 ‐> group by state ‐> order by seq;+‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐+| seq | state | numb_ops | sum_dur | avg_dur | sum_cpu | avg_cpu |+‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐+| 0 | (initialization) | 1 | 0.00004 | 0.00004 | 0.00000 | 0.00000 || 1 | Opening tables | 1 | 0.00023 | 0.00023 | 0.00000 | 0.00000 || 2 | System lock | 1 | 0.00001 | 0.00001 | 0.00000 | 0.00000 || 3 | Table lock | 1 | 0.00001 | 0.00001 | 0.00000 | 0.00000 || 4 | checking permissions | 1 | 0.00010 | 0.00010 | 0.00000 | 0.00000 || 5 | optimizing | 4 | 0.00004 | 0.00001 | 0.00000 | 0.00000 || 6 | statistics | 4 | 0.00007 | 0.00002 | 0.00100 | 0.00025 || 7 | preparing | 4 | 0.00005 | 0.00001 | 0.00000 | 0.00000 || 8 | Creating tmp table | 1 | 0.00003 | 0.00003 | 0.00000 | 0.00000 || 9 | executing | 37352 | 0.16631 | 0.00000 | 0.05899 | 0.00000 || 10 | Copying to tmp table | 1 | 0.00006 | 0.00006 | 0.00000 | 0.00000 || 15 | Sending data | 37353 | 3.85151 | 0.00010 | 3.72943 | 0.00010 || 74717 | Sorting result | 1 | 0.00112 | 0.00112 | 0.00100 | 0.00100 || 74719 | removing tmp table | 2 | 0.00003 | 0.00001 | 0.00000 | 0.00000 || 74721 | init | 1 | 0.00002 | 0.00002 | 0.00000 | 0.00000 || 74727 | end | 1 | 0.00001 | 0.00001 | 0.00000 | 0.00000 || 74728 | query end | 1 | 0.00000 | 0.00000 | 0.00000 | 0.00000 || 74729 | freeing items | 1 | 0.00002 | 0.00002 | 0.00000 | 0.00000 || 74730 | closing tables | 2 | 0.00001 | 0.00001 | 0.00000 | 0.00000 || 74733 | logging slow query | 1 | 0.00000 | 0.00000 | 0.00000 | 0.00000 |+‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐+

But...

• Only in 5.0

• 5.1 implementation under review

• http://forge.mysql.com/wiki/Testing_Show_Profiles_5_1

http://forge.mysql.com/wiki/Testing_Show_Profiles_5_1




8Know what’s going on

Usage statistics

SHOW STATUSmysql> SHOW STATUS LIKE 'Com_select';+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐+| Variable_name | Value |+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐+| Com_select | 13 | +‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐+1 row in set (1.65 sec)

mysql> SELECT 1;+‐‐‐+| 1 |+‐‐‐+| 1 | +‐‐‐+1 row in set (0.00 sec)

mysql> SHOW STATUS LIKE 'Com_select';+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐+| Variable_name | Value |+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐+| Com_select | 14 | +‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐+1 row in set (0.00 sec)

External tools

• mysqlsla

http://hackmysql.com/mysqlsla

mysqlsla parses, filters, analyzes and sorts MySQL slow, general, binary and microslow patched logs in order to create a customizable report of the queries and their meta-property values.



External tools• mysqlidxchk

http://hackmysql.com/mysqlidxchk

mysqlidxchk (MySQL Index Checker) checks MySQL databases/tables for unused indexes. Given one or more slow, general, or "raw" log files, mysqlidxchk reports which indexes in the database schema are not used by the queries in the log files.



9Understanding

REPLACE

mysql> CREATE TABLE fk_relations ( ‐> key1 INT NOT NULL PRIMARY KEY, ‐> key2 INT NOT NULL UNIQUE ‐> );Query OK, 0 rows affected (0.02 sec)

mysql> INSERT INTO fk_relations VALUES (1,1), (2,2);Query OK, 2 rows affected (0.00 sec)Records: 2 Duplicates: 0 Warnings: 0

mysql> SELECT * FROM fk_relations;+‐‐‐‐‐‐+‐‐‐‐‐‐+| key1 | key2 |+‐‐‐‐‐‐+‐‐‐‐‐‐+| 1 | 1 | | 2 | 2 | +‐‐‐‐‐‐+‐‐‐‐‐‐+2 rows in set (0.00 sec)

mysql> REPLACE INTO fk_relations VALUES (1,3);Query OK, 2 rows affected (0.03 sec)


mysql> SELECT * FROM fk_relations;+‐‐‐‐‐‐+‐‐‐‐‐‐+| key1 | key2 |+‐‐‐‐‐‐+‐‐‐‐‐‐+| 1 | 3 | | 2 | 2 | +‐‐‐‐‐‐+‐‐‐‐‐‐+2 rows in set (0.00 sec)


???


mysql> SELECT * FROM fk_relations;+‐‐‐‐‐‐+‐‐‐‐‐‐+| key1 | key2 |+‐‐‐‐‐‐+‐‐‐‐‐‐+| 1 | 2 | +‐‐‐‐‐‐+‐‐‐‐‐‐+1 row in set (0.00 sec)

+‐‐‐‐‐‐+‐‐‐‐‐‐+| key1 | key2 |+‐‐‐‐‐‐+‐‐‐‐‐‐+| 1 | 3 | | 2 | 2 | +‐‐‐‐‐‐+‐‐‐‐‐‐+

mysql> REPLACE INTO fk_relations VALUES (1,2);‐‐ Equals...

+‐‐‐‐‐‐+‐‐‐‐‐‐+| key1 | key2 |+‐‐‐‐‐‐+‐‐‐‐‐‐+| 1 | 3 | | 2 | 2 | +‐‐‐‐‐‐+‐‐‐‐‐‐+

mysql> REPLACE INTO fk_relations VALUES (1,2);‐‐ Equals...‐‐ key1 is PKmysql> DELETE FROM fk_relations WHERE key1 = 1;

+‐‐‐‐‐‐+‐‐‐‐‐‐+| key1 | key2 |+‐‐‐‐‐‐+‐‐‐‐‐‐+| 2 | 2 | +‐‐‐‐‐‐+‐‐‐‐‐‐+

mysql> REPLACE INTO fk_relations VALUES (1,2);‐‐ Equals...‐‐ key1 is PKmysql> DELETE FROM fk_relations WHERE key1 = 1;‐‐ key2 is Uniquemysql> DELETE FROM fk_relations WHERE key2 = 2;

+‐‐‐‐‐‐+‐‐‐‐‐‐+| key1 | key2 |+‐‐‐‐‐‐+‐‐‐‐‐‐+| 1 | 2 | +‐‐‐‐‐‐+‐‐‐‐‐‐+

mysql> REPLACE INTO fk_relations VALUES (1,2);‐‐ Equals...‐‐ key1 is PKmysql> DELETE FROM fk_relations WHERE key1 = 1;‐‐ key2 is Uniquemysql> DELETE FROM fk_relations WHERE key2 = 2;mysql> INSERT INTO fk_relations VALUES (1,2);

That’s whymysql> REPLACE INTO fk_relations VALUES (1,2);Query OK, 3 rows affected (0.06 sec)


That’s whymysql> REPLACE INTO fk_relations VALUES (1,2);Query OK, 3 rows affected (0.06 sec)


2 deletes + 1 insert

10The good and bad

about temporary tables

Performance

• Be careful with complex queries

• Extremely slow on large datasets

• Use summary tables instead

Too complexselect d.dept_name, SUM(salary) from departments d LEFT JOIN dept_emp de USING (dept_no) LEFT JOIN salaries s USING (emp_no) where s.from_date >= '2000‐01‐01' and s.to_date < '2001‐01‐01' group by dept_no;

Instead, split in twoselect d.dept_name, SUM(salary) from departments d LEFT JOIN dept_emp de USING (dept_no) LEFT JOIN salaries s USING (emp_no) where s.from_date >= '2000‐01‐01' and s.to_date < '2001‐01‐01' group by dept_no;

CREATE TEMPORARY TABLE salaries2000 SELECT * FROM salaries s WHERE s.from_date >= '2000‐01‐01' AND s.to_date < '2001‐01‐01';

SELECT d.dept_name, SUM(salary) FROM departments d LEFT JOIN dept_emp de USING (dept_no) LEFT JOIN salaries2000 s USING (emp_no) GROUP BY dept_no;

Big performance gain(If indexes are in their place)

Big performance gain(If indexes are in their place)

I’ve seen 10X!

one more thing...

one more thing...I had to do it ;-)

Shit happensmysql> select * from t;+‐‐‐‐‐‐+| id |+‐‐‐‐‐‐+| 2 | +‐‐‐‐‐‐+1 row in set (0.00 sec)

mysql> drop table t;Query OK, 0 rows affected (0.04 sec)


mysql> drop table t;ERROR 1051 (42S02): Unknown table 't'

WTF?!?

Some seconds ago...

mysql> select * from t;+‐‐‐‐+| id |+‐‐‐‐+| 1 | +‐‐‐‐+1 row in set (0.00 sec)

mysql> create temporary table t(id int);Query OK, 0 rows affected (0.08 sec)

mysql> select * from t;Empty set (0.00 sec)

mysql> insert into t values (2);Query OK, 1 row affected (0.05 sec)

mysql> select * from t;+‐‐‐‐‐‐+| id |+‐‐‐‐‐‐+| 2 | +‐‐‐‐‐‐+1 row in set (0.00 sec)

WTF?!?...again

• Temporary tables exist per session

• Be careful using connection pools

• They overlap current tables

There’s a reason for everythingmysql> select * from t;+‐‐‐‐‐‐+| id |+‐‐‐‐‐‐+| 2 | +‐‐‐‐‐‐+1 row in set (0.00 sec)


mysql> select * from t;+‐‐‐‐+| id |+‐‐‐‐+| 1 | +‐‐‐‐+1 row in set (0.00 sec)


mysql> drop table t;ERROR 1051 (42S02): Unknown table 't'

temporary

regular

• MySQL Proxy

https://launchpad.net/mysql-proxy

• MySQL Sandbox

https://launchpad.net/mysql-sandbox

• MySQL Random Query Generator

https://launchpad.net/randgen

What else?







Questions?Probably out of time at this point, but it’s the standard

Thanks!

10 things you might not know about mysql

Technology