https://www.fromdual.com/tags/hint/Recent content in Hint on FromDual GmbHHugoen-GBoli.sennhauser@fromdual.com (Oli Sennhauser)oli.sennhauser@fromdual.com (Oli Sennhauser)© FromDual GmbHMon, 09 Feb 2026 12:10:00 +0100https://www.fromdual.com/blog/how-the-mysql-optimizer-is-cheating-you/Mon, 17 May 2010 20:10:23 +0000oli.sennhauser@fromdual.com (Oli Sennhauser)https://www.fromdual.com/blog/how-the-mysql-optimizer-is-cheating-you/<p>At a customer we had a nice example of how the MySQL Optimizer is cheating when used in combination with the MySQL Cluster. The customer had queries running not too slow in the development environment but when he tried them on the acceptance test environment (with more data) the query was running much too long which was unacceptable because this query can occur many times per second.</p>https://www.fromdual.com/blog/mysql-hints/Mon, 15 Mar 2010 13:38:54 +0000oli.sennhauser@fromdual.com (Oli Sennhauser)https://www.fromdual.com/blog/mysql-hints/<h2 id="table-of-contents">Table of Contents</h2> <ul> <li><a href="#temp_sequence">Result set with temporary sequence</a></li> <li><a href="https://www.fromdual.com/blog/mysql-hints/#prefixed_indexes">Determination of optimal length of prefixed indexes</a></li> <li><a href="https://www.fromdual.com/blog/mysql-hints/#ddl">Using MySQL keywords in table or columm names</a></li> <li><a href="https://www.fromdual.com/blog/mysql-hints/#missing_pk_index">Missing Primary Key Index</a></li> <li><a href="https://www.fromdual.com/blog/mysql-hints/#libaio">Problems while installing a MySQL 5.5 database</a></li> <li><a href="https://www.fromdual.com/blog/mysql-hints/#sequence">InnoDB AUTO_INCREMENT at 2^nd position</a></li> </ul> <p><span id="temp_sequence"></span></p>https://www.fromdual.com/blog/mysql-performance-schema-hints/Sun, 14 Jul 2013 09:29:09 +0200oli.sennhauser@fromdual.com (Oli Sennhauser)https://www.fromdual.com/blog/mysql-performance-schema-hints/<h2 id="table-of-contents">Table of Contents</h2> <ul> <li><a href="#accounts-not-properly-closing">Accounts not properly closing connections</a></li> <li><a href="#unused-indexes">Unused indexes</a></li> <li><a href="#who-created-temporary-tables">Who created temporary (disk) tables</a></li> <li><a href="#accounts-which-never-connected">Accounts which never connected since last start-up</a></li> <li><a href="#user-which-never-connected">Users which never connected since last start-up</a></li> <li><a href="#totally-unused-accounts">Totally unused accounts (never connected since last restart and not used to check Stored Program or View privileges) since last start-up</a></li> <li><a href="#show-full-processlist"><code>SHOW FULL PROCESSLIST</code></a></li> <li><a href="#storage-engine-per-schema">Storage Engines per schema</a></li> <li><a href="#tables-without-primary-key">Tables without a Primary Key</a></li> <li><a href="#bad-sql-queries-of-users">Bad SQL queries of users</a></li> <li><a href="#show-profile-in-performance_schema"><code>SHOW PROFILE</code> in <code>PERFORMANCE_SCHEMA</code></a></li> <li><a href="#select-insert-update-and-delete-per-table"><code>SELECT</code>, <code>INSERT</code>, <code>UPDATE</code> and <code>DELETE</code> per table</a></li> <li><a href="#top-long-running-queries">Top long running queries</a></li> <li><a href="#tables-never-written-to">Tables never written to</a></li> <li><a href="#dml-ddl-dcl-per-account">DML, DDL and DCL per account</a></li> <li><a href="#erroneous-mysql-queries">Finding syntactically wrong/erroneous MySQL queries</a></li> <li><a href="#finding-queries-served-by-query-cache">Finding queries served by MySQL Query Cache</a></li> <li><a href="#grant-sys-schema-access">Grant access to <code>sys</code> schema to another user</a></li> <li><a href="#grant-ps-schema-access">Grant access to <code>PERFORMANCE_SCHEMA</code> schema to another user</a></li> <li><a href="#innodb-locks">Find InnoDB Locks</a></li> <li><a href="#metadata-locks">Find Metadata Locks</a></li> <li><a href="#statements-before-sleep">What did a Connection before sleeping?</a></li> <li><a href="#how-many-statements-did-another-connection">How many statements did another (sleeping) connection?</a></li> <li><a href="%22/blog/myisam-locking-and-who-is-the-evil#performance-schema%22" title="MyISAM locking and who is the evil?">MyISAM locking</a></li> <li><a href="#connections-per-user">Connections per user</a></li> <li><a href="#connections-per-user-and-ip">Connections per user and IP</a></li> <li><a href="#accounts-which-could-not-connect">Accounts which could not connect or with connection errors</a></li> <li><a href="#temporary-tables-filling-disk">Temporary tables filling my disk</a></li> <li><a href="#who-is-writing-to-the-binary-log">Who is writing to the binary log</a></li> <li><a href="#average-binlog-transaction-size">Average binlog transaction size</a></li> <li><a href="#result-size-of-select-statement">Result size of <code>SELECT</code> statement</a></li> <li><a href="#find-open-long-running-transactions">Find open long running transactions</a></li> </ul> <h2 id="mariadb">MariaDB</h2> <p>On MariaDB you have to enable the Performance Schema first before use:</p>