MySQL

Links

• Downloads

• A Quick Guide to Using the MySQL APT Repository

Documentation

• Homepage
• Documentation
• MySQL Tutorial
• MySQL Cheat Sheet
• A collection of mysql commands
• MySQL C API Functions
• Avoid This When Tuning MySQL Query Cache for Performance
• MySQL joins
• MySQLForge Wiki
• Common mysql queries
• http://people.freebsd.org/~kris/scaling/mysql.html
• http://zabbixzone.com/zabbix/mysql-performance-tips-for-zabbix/
• Migratie mysql database without downtime
• 10 things to monitor on your mysql server
• MySQL Replication
• Mariadb error codes
• Client error reference

• Fragmented tables

 

Data types

https://dev.mysql.com/doc/refman/8.0/en/data-types.html

 

 

Tools

• Adminer (check out! )
• phpmyadmin
• http://phpminiadmin.sourceforge.net/
• MySQL memory calculator

Create a diagram

• Create a dia diagram

Show syntax

http://dev.mysql.com/doc/refman/5.1/en/show.html

Tuning MySQL

• http://www.mysqlperformanceblog.com/
• Optimizing MySQL server variables
• mytop
• mysqltuner

In my.cnf check out:

log_slow_queries

On prompt check out stuff like:

SHOW STATUS LIKE '%qcache%';
SHOW GLOBAL STATUS;
SHOW VARIABLES;

 

• 5.1.5 Status Variables
• Tuning MysQL

 

Benchmarking

mysqlslap

• mysqlslap documentation

 

HOWTO

Reset auto increment

ALTER TABLE tablename AUTO_INCREMENT = 1

FAQ

Finding mysql configuration files

On Ubuntu

mysqld: /etc/mysql/mysql.conf.d/mysqld.cnf

ERROR 1231 (42000): Variable 'slow_query_log_file' can't be set to the value of '/var/log/mysql-slow.log'

Means the file doesn't exist, create it and chown mysql.mysql ( or similar )

Accounts

https://dev.mysql.com/doc/refman/8.0/en/show-grants.html

show grants
revoke 

Set password to user on auth_socket

This just changes from auth_socket to password

alter user 'root'@'localhost' identified with caching_sha2_password by 's3cr37';
flush privileges;

change password

alter user 'foo'@'localhost' identified by 's3cr3t5';

seems this no longer works on ubuntu/mysql8? nor does

mysqladmin -u root --password

Clustering

Check out percona galera (and xtrabackup)

Misc

server went away

• can be triggered by max_packet_size

 

 

stop query

show processlist
kill <id of query>

 

InnoDB: Error: log file ./ib_logfile0 is of different size 0 5242880 bytes

(re)move ib_logfile[01]

 

run query in script

RES=`mysql -qsBe "select foo from fu.bar where tap ='beer'" -N`

where did mysql_config_editor go?

https://mariadb.com/resources/blog/mysql-56-security-through-complacency explains how no security is better than some security

high memory usage

• https://bobcares.com/blog/fix-mysql-high-memory-usage/

fix logrotate on debian

echo "SET PASSWORD FOR 'debian-sys-maint'@'localhost' = PASSWORD('`grep password /etc/mysql/debian.cnf | head -n 1 | awk -F= '{ gsub(/[ \t]+/, "", $2); print $2 }'`');" | mysql -u root -p

insert select

 insert into bar(c,d) select concat ("foo ",w) as  c, concat("bar ",w) as d from foo;

 

slow imports

https://support.tigertech.net/mysql-large-inserts

speed up import from dump

SET autocommit=0;
SET unique_checks=0;
SET foreign_key_checks=0;

and after import

COMMIT;
SET autocommit=1;
SET unique_checks=1;
SET foreign_key_checks=1;

and turn them back on

and try mysqldump --extended-insert (this seems to be default now, and part of --opt)

pagination in CLI

show tables;\P less

show mysql configuration

show variables

 

show performance

show innodb status

or

SHOW ENGINE INNODB STATUS

 

mysql error codes

http://dev.mysql.com/doc/refman/5.1/en/error-messages-client.html

 

 

mysqldump

separate lines in mysqldump

--extended-insert=FALSE --complete-insert=TRUE 

maximum statement execution time exceeded when dumping table

max_execution_time

mysqldump: out of memory

mysqldump -q

mysqldump: MySQL server has gone away (2006)

seems related to max_allowed_packet RTENOTITLE

mysqldump: Dumping 'information_schema' DB content is not supported

Just don't try to dump it :)

Warning: /usr/bin/mysqldump: ignoring option '--databases' due to invalid value 'mysql'

Check your ~/.my.cnf

Other stuff

Fix privileges

mysql_fix_privilege_tables

 

clean up mysql-bin

purge logs;
purge binary logs to 'mysql-bin.xxxyy';

ERROR 2013 (HY000): Lost connection to MySQL server at 'reading initial communication packet', system error: 0

Could be /etc/hosts.allow

ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction

SHOW ENGINE INNODB STATUS

will probably provide clues, it might well be a matter of reducing load/qps

error 1146 Table 'performance_schema.session_variables' doesn't exist

Run mysql_upgrade and restart mysqld

ERROR 1410 (42000): You are not allowed to create a user with GRANT

First create user:

create user 'foo'@'localhost' identified by 'topsecret';

then

grant all privileges on foobar.* to 'foo'@'localhost';
flush privileges;

OR maybe you got wrong host for the user, like 'localhost' instead of '%'

show table sizes

SELECT table_schema as `Database`, table_name AS `Table`, round(((data_length + index_length) / 1024 / 1024), 2) `Size in MB`  FROM information_schema.TABLES  ORDER BY (data_length + index_length) DESC;

 

show database sizes

SELECT table_schema "DB Name", ROUND(SUM(data_length + index_length) / 1024 / 1024, 1) "DB Size in MB" FROM 
information_schema.tables 
GROUP BY table_schema; 

InnoDB: page_cleaner: 1000ms intended loop took 16955ms. The settings might not be optimal.

???

 

ERROR 1010 (HY000): Error dropping database (can't rmdir './foo', errno: 39)

Files in $datadir/foo mysql doesn't know about

 

privileges for SHOW GLOBAL STATUS

CREATE USER 'zbx_monitor'@'localhost' IDENTIFIED BY '<password>';
GRANT REPLICATION CLIENT,PROCESS,SHOW DATABASES,SHOW VIEW ON *.* TO 'zbx_monitor'@'localhost';

Check fragmentation

select ENGINE,
 concat(TABLE_SCHEMA, '.', TABLE_NAME) as table_name,
 round(DATA_LENGTH/1024/1024, 2) as data_length,
 round(INDEX_LENGTH/1024/1024, 2) as index_length,
 round(DATA_FREE/1024/1024, 2) as data_free,
 (data_free/(index_length+data_length)) as frag_ratio
FROM information_schema.tables
WHERE DATA_FREE > 0
ORDER BY frag_ratio DESC;

Show processes

SELECT * from INFORMATION_SCHEMA.PROCESSLIST
show full processlist

Tips & Tricks

save password

 mysql_config_editor set --host=localhost --user=root --password

(due to serious crappiness you might have to quote the password)

On newer versions this no longer works, and you have to fall back to using ~/.my.cnf

[client]
user=root
password=s3cr3t

set pager

pager less;

and to disable it again:

nopager;