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| == MySQL == | | == MySQL == |
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| === Performance Tuning ===
| | [[MySQL#Performance_Tuning | MySQL Performance Tuning]] |
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| '''1. First, Check innodb and myisam settings'''
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| Run the below to get the size of data in INNODB and MYISAM tables:<br />
| | == OOM Killer == |
| <pre>mysql -e 'SELECT SQL_NO_CACHE Engine, count(*) "# of Tables", concat(round(sum(table_rows)/1000,2),"K") "Rows", concat(round(sum(data_length)/(1024*1024),2),"M") "Size of Data", concat(round(sum(index_length)/(1024*1024),2),"M") "Size of Indexes", concat(round(sum(data_length+index_length)/(1024*1024),2),"M") "Total Size", concat(round(sum(index_length)/sum(data_length)*(100),2), "%") "% Data in Indexes" FROM information_schema.TABLES GROUP BY engine ORDER BY sum(data_length+index_length) DESC LIMIT 10;'</pre>
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| In /etc/my.cnf, change:<br />
| | OOM Killer kills the process with the highest memory usage to prevent the system from running out of memory. It often triggers due to memory load. |
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| <code>innodb_buffer_pool_size</code> - set this to the value from the Total column, innodb row.<br />
| | === Prevent OOM Killer from killing MySQL === |
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| '''Note:''' if server has lots of RAM, and lots of data, set the innodb_buffer_pool_size = 1G, then set innodb_buffer_pool_instances = 4 (or smaller, or larger, depending on RAM) Also note that this will set the buffer pool size as 1G, and break that 1G into 4 chunks (It will NOT create 4, 1GB pools.)
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| <code>key_buffer_size</code> - set this to the value from the Index column, myisam row. | | You can create a cron job to keep the PID for MySQL updated in the OOM Killer exclusion list: |
| | <code>*/1 * * * * root pgrep -f "/usr/bin/mysql" | while read PID; do echo -1000 > /proc/$PID/oom_score_adj; done</code> |
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| '''2. Opens'''
| | == References == |
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| a.) Get the total number of tables on the server:<br />
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| <code>find /var/lib/mysql -name '*.frm' | wc -l</code> - Example output: 4568 | | <li>[https://backdrift.org/oom-killer-how-to-create-oom-exclusions-in-linux Backdrift.org - OOM Killer exclusions]</li> |
| | | </ul> |
| b.) Set table_open_cache variable in /etc/my.cnf to 30% of that number<br />
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| Example, based on the above number: <code>table_open_cache = 1371</code>
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| c.) Set open_files_limit to three times the corrected value of table_open_cache<br />
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| Example: <code>open_files_limit = 3951</code>
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| You can check to see if this value is good by running <code>mysqladmin stat</code>. That command will show the number of Opens, and the number of Open tables. Ideally, these numbers should be identical.
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| === MySQL Error log ===
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| To check the MySQL error log, run:<br />
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| <code>mysql -e "show variables like '%log_error%';"</code>
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| This will show the location of the MySQL error log, which you can then grep, tail, etc. (You're looking for stuff like innodb errors, disk space issues, connection messages, etc)
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| === View MySQL Variables ===
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| You can view the variables that MySQL is using with:
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| <code>mysql -e "show variables like 'max_connections%';" </code> - This shows the max_connections variable. You can substitute any MySQL variable here.
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| This is helpful for database connection errors, or if a change to /etc/my.cnf isn't 'sticking' (In that case, look for other my.cnf files)
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| === View Currently Running Queries ===
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| <code>mysqladmin process stat</code> - This will show the queries that are running, how many threads, Open tables, slow queries, and a bunch of other helpful stuff. (Note that you can "tail -f" by running: <code>watch mysqladmin process stat</code> )
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MySQL
MySQL Performance Tuning
OOM Killer
OOM Killer kills the process with the highest memory usage to prevent the system from running out of memory. It often triggers due to memory load.
Prevent OOM Killer from killing MySQL
You can create a cron job to keep the PID for MySQL updated in the OOM Killer exclusion list:
*/1 * * * * root pgrep -f "/usr/bin/mysql" | while read PID; do echo -1000 > /proc/$PID/oom_score_adj; done
References