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https://dev.mysql.com/doc/refman/8.0/en/performance-schema-setup-instruments-table.html
The setup_instruments table lists classes of instrumented objects for which events can be collected: mysql> SELECT * FROM performance_schema.setup_instruments\G *************************** 1. row *************************** NAME: ...At this point, ...
https://dev.mysql.com/doc/refman/8.0/en/information-schema-tables-table.html
The information_schema_stats_expiry system variable defines the period of time before cached table statistics expire. To update cached values at any time for a given table, use ANALYZE TABLE. With the removal of .frm files in MySQL 8.0, this column ...If there are no cached statistics or statistics have expired, statistics are retrieved from storage engines when querying table statistics ...
https://dev.mysql.com/doc/refman/8.0/en/cost-model.html
These estimates are stored in the server_cost and engine_cost tables in the mysql system database and are configurable at any time. Cost Model General Operation The Cost Model Database Making Changes to the Cost Model Database Cost Model General ...
https://dev.mysql.com/doc/refman/8.0/en/group-replication-upgrading-member.html
If the primary is upgraded before a secondary, a new primary using the older MySQL version is chosen, but there is no need for this step. Important If an upgraded member has group_replication_start_on_boot=1 then it could rejoin the group before you ... This section explains the steps required for upgrading a member of a ...
https://dev.mysql.com/doc/refman/8.0/en/subquery-materialization.html
The first time MySQL needs the subquery result, it materializes that result into a temporary table. Any subsequent time the result is needed, MySQL refers again to the temporary table. If materialization is not used, the optimizer sometimes rewrites ... The optimizer uses materialization to enable more efficient subquery ...
https://dev.mysql.com/doc/refman/8.0/en/subquery-restrictions.html
In MySQL, it can produce nondeterministic results because f() might be executed a different number of times for different executions of a given query depending on how the optimizer chooses to handle it. FROM t...) AS dt ...); Here the result from ...
https://dev.mysql.com/doc/refman/8.0/en/replication-features-functions.html
To avoid unexpected results when replicating between MySQL servers in different time zones, set the time zone on both source and replica. To explain the potential problems when replicating between servers which are in different time zones, suppose ... Certain functions do not replicate well under some conditions: The USER(), CURRENT_USER() (or CURRENT_USER), UUID(), VERSION(), and LOAD_FILE() functions are replicated without change and thus do not work reliably on the replica unless row-based replication is ...
https://dev.mysql.com/doc/refman/8.0/en/charset-unicode-utf8.html
utf8mb3 remains supported for the lifetimes of the MySQL 8.0.x and following LTS release series, as well as in MySQL 8.0. utf8 has been used by MySQL in the past as an alias for the utf8mb3 character set, but this usage is now deprecated; in MySQL ...For more information, see Section 12.9.2, “The utf8mb3 Character Set (3-Byte UTF-8 Unicode ...
https://dev.mysql.com/doc/refman/8.0/en/charset-unicode-utf8mb3.html
utf8mb3 remains supported for the lifetimes of the MySQL 8.0.x and following LTS release series, as well as in MySQL 8.0. Expect utf8mb3 to be removed in a future major release of MySQL. Since changing character sets can be a complex and ... The ...
https://dev.mysql.com/doc/refman/8.0/en/index-statistics.html
When a given index value yields a large number of rows, the index is less useful and MySQL is less likely to use it. This affects ref accesses for comparisons of the form tbl_name.key = expr: MySQL does not access the table if the current value of ... Storage engines collect statistics about tables for use by the ...