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https://dev.mysql.com/doc/refman/8.0/en/information-schema-statistics-table.html
The higher the cardinality, the greater the chance that MySQL uses the index when doing joins. The information_schema_stats_expiry system variable defines the period of time before cached table statistics expire. If there are no cached statistics or ...
https://dev.mysql.com/doc/refman/8.0/en/innodb-adaptive-hash.html
Access to the adaptive hash index can sometimes become a source of contention under heavy workloads, such as multiple concurrent joins. The adaptive hash index enables InnoDB to perform more like an in-memory database on systems with appropriate ...
https://dev.mysql.com/doc/refman/8.0/en/innodb-memcached-porting-mysql.html
Consider these aspects of memcached applications when adapting an existing MySQL schema or application to use the daemon_memcached plugin: memcached keys cannot contain spaces or newlines, because these characters are used as separators in the ...
https://dev.mysql.com/doc/refman/8.0/en/innodb-parameters.html
innodb_thread_sleep_delay Command-Line Format --innodb-thread-sleep-delay=# System Variable innodb_thread_sleep_delay Scope Global Dynamic Yes SET_VAR Hint Applies No Type Integer Default Value 10000 Minimum Value 0 Maximum Value 1000000 Unit ...
https://dev.mysql.com/doc/refman/8.0/en/innodb-performance-thread_concurrency.html
Since an SQL statement (such as a join) may comprise multiple row operations within InnoDB, InnoDB assigns a specified number of “tickets” that allow a thread to be scheduled repeatedly with minimal overhead. InnoDB uses operating system ...
https://dev.mysql.com/doc/refman/8.0/en/innodb-statistics-estimation.html
This technique is especially important for large tables and tables used in joins. Optimizer statistics are not persisted to disk when innodb_stats_persistent=OFF or when individual tables are created or altered with STATS_PERSISTENT=0. Instead, ...
https://dev.mysql.com/doc/refman/8.0/en/innodb-transaction-isolation-levels.html
Transaction isolation is one of the foundations of database processing. Isolation is the I in the acronym ACID; the isolation level is the setting that fine-tunes the balance between performance and reliability, consistency, and reproducibility of ...
https://dev.mysql.com/doc/refman/8.0/en/insert-on-duplicate.html
References to columns from queries on a join over multiple tables. If you specify an ON DUPLICATE KEY UPDATE clause and a row to be inserted would cause a duplicate value in a UNIQUE index or PRIMARY KEY, an UPDATE of the old row occurs. If column ...
https://dev.mysql.com/doc/refman/8.0/en/internal-temporary-tables.html
Tables created for subquery or semijoin materialization (see Section 10.2.2, “Optimizing Subqueries, Derived Tables, View References, and Common Table Expressions”). Evaluation of statements that contain an ORDER BY clause and a different GROUP ... In some cases, the server creates internal temporary tables while processing ...
https://dev.mysql.com/doc/refman/8.0/en/invisible-columns.html
An invisible column is normally hidden to queries, but can be accessed if explicitly referenced. As an illustration of when invisible columns may be useful, suppose that an application uses SELECT * queries to access a table, and must continue to ...