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MySQL Lock Contention
- Identify the queries causing lock contention by checking the `INFORMATIONSCHEMA.INNODBLOCKS` and `INFORMATIONSCHEMA.INNODBLOCK_WAITS` tables. Use this query to find which transactions are waiting for locks:
SELECT * FROM INFORMATIONSCHEMA.INNODBLOCK_WAITS w
INNER JOIN INFORMATIONSCHEMA.INNODBLOCKS l1 ON w.REQUESTINGTRXID = l1.LOCKTRXID
INNER JOIN INFORMATIONSCHEMA.INNODBLOCKS l2 ON w.BLOCKINGTRXID = l2.LOCKTRXID;
- Check which transactions are currently running and might be causing the locks. Execute the following to see the running transactions:
SHOW ENGINE INNODB STATUS\G
Look for the `TRANSACTIONS` section.
- Identify long-running transactions that might be responsible for the contention. Use:
SELECT trxid, trxstate, trxstarted, trxrequestedlockid, trxwaitstarted, trxweight, trxmysqlthreadid, trx_query
FROM informationschema.innodbtrx
ORDER BY trx_started;
- Kill the transaction that is causing the lock contention, if it's safe to do so, to free up the lock. Use the MySQL `KILL` command followed by the thread ID:
KILL THREAD_ID;
Replace `THREADID` with the `trxmysqlthreadid` from the query in step 3.
- Analyze the slow query log to understand why these queries are causing lock contention. Enable it if it's not already enabled:
SET GLOBAL slowquerylog = 'ON';
SET GLOBAL slowquerylog_file = '/path/to/your/log/file.log';
SET GLOBAL longquerytime = 2;
Adjust the `longquerytime` value as needed.
- Optimize the queries identified in step 1. Look at the execution plan using `EXPLAIN` and consider adding indexes, rewriting the query, or splitting a long transaction into smaller parts.
EXPLAIN SELECT * FROM yourtable WHERE yourconditions;
Replace the `SELECT` statement with the query causing lock contention.
These are immediate actions you can take to identify and potentially resolve lock contention issues in your MySQL database.
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