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https://dev.mysql.com/doc/refman/8.4/en/limit-optimization.html
MySQL sometimes optimizes a query that has a LIMIT row_count clause and no HAVING clause: If you select only a few rows with LIMIT, MySQL uses indexes in some cases when normally it would prefer to do a full table scan. If the server uses temporary ... If you need only a specified number of rows from a result set, use a LIMIT clause in the query, rather than fetching the whole result set and throwing away the extra ...
https://dev.mysql.com/doc/refman/8.4/en/myisam-key-cache.html
It employs a cache mechanism to keep the most frequently accessed table blocks in memory: For index blocks, a special structure called the key cache (or key buffer) is maintained. You can set up multiple key caches and assign table indexes to ... To ...
https://dev.mysql.com/doc/refman/8.4/en/myisamchk-other-options.html
myisamchk supports the following options for actions other than table checks and repairs: --analyze, -a Command-Line Format --analyze Analyze the distribution of key values. This improves join performance by enabling the join optimizer to better ...
https://dev.mysql.com/doc/refman/8.4/en/mysql-cluster-disk-data-storage-requirements.html
The following items apply to Disk Data storage requirements: Variable-length columns of Disk Data tables take up a fixed amount of space. You can obtain an estimate the amount of space available in data files and undo log files by querying the ...
https://dev.mysql.com/doc/refman/8.4/en/mysql-cluster-programs-ndb-size-pl.html
Options that can be used with ndb_size.pl are shown in the following table. Similarly, you can cause specific tables to be skipped by listing their names, separated by commas, following the optional --excludetables option. Memory requirements for ...
https://dev.mysql.com/doc/refman/8.4/en/mysql-cluster-sql-statements.html
However, you can use LIKE to filter queries against the Information Schema ENGINES table, as discussed in the next item. SELECT * FROM INFORMATION_SCHEMA.ENGINES [WHERE ENGINE LIKE 'NDB%'] This is the equivalent of SHOW ENGINES, but uses the ENGINES ... This section discusses several SQL statements that can prove useful in managing and monitoring a MySQL server that is connected to an NDB Cluster, and in some cases provide information about the cluster ...
https://dev.mysql.com/doc/refman/8.4/en/outer-join-simplification.html
Table expressions in the FROM clause of a query are simplified in many cases. When the optimizer evaluates plans for outer join operations, it takes into consideration only plans where, for each such operation, the outer tables are accessed before ...At the parser stage, queries with right outer join operations are converted to equivalent queries containing only left join ...
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-atom-molecule-events.html
For a table I/O event, there are usually two rows in events_waits_current, not one. For example, a row fetch might result in rows like this: Row# EVENT_NAME TIMER_START TIMER_END ---- ---------- ----------- --------- 1 wait/io/file/myisam/dfile ...
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-query-profiling.html
The setup_actors table can be used to limit the collection of historical events by host, user, or account to reduce runtime overhead and the amount of data collected in history tables. For example: mysql> SELECT * FROM employees.employees WHERE ...
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-runtime-configuration.html
If you have the UPDATE privilege, you can change Performance Schema operation by modifying setup tables to affect how monitoring occurs. For additional details about these tables, see Section 29.12.2, “Performance Schema Setup Tables”. The ...