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https://dev.mysql.com/doc/refman/8.4/en/getting-information.html
To find out which database is currently selected, use the DATABASE() function: mysql> SELECT DATABASE(); +------------+ | DATABASE() | +------------+ | menagerie | +------------+ If you have not yet selected any database, the result is NULL. What ...
https://dev.mysql.com/doc/refman/8.4/en/group-replication-communication-protocol.html
For example: SELECT group_replication_set_communication_protocol("5.7.25"); If you upgrade all the members of a replication group to a new MySQL Server release, the group's communication protocol version is not automatically upgraded to match. For ... Group Replication in MySQL 8.4 uses the concept of a group communication protocol whose version can be managed explicitly, and set to accommodate the oldest MySQL Server version that you want the group to ...
https://dev.mysql.com/doc/refman/8.4/en/group-replication-functions-for-member-actions.html
Example: SELECT group_replication_disable_member_action("mysql_disable_super_read_only_if_primary", "AFTER_PRIMARY_ELECTION"); For more information, see Section 20.5.1.5, “Configuring Member Actions”. Example: SELECT ... The following functions ...
https://dev.mysql.com/doc/refman/8.4/en/information-schema-innodb-trx-table.html
To resolve a deadlock, InnoDB selects the transaction with the smallest weight as the “victim” to roll back. TRX_AUTOCOMMIT_NON_LOCKING A value of 1 indicates the transaction is a SELECT statement that does not use the FOR UPDATE or LOCK IN ...
https://dev.mysql.com/doc/refman/8.4/en/innodb-deadlocks.html
A deadlock can occur when transactions lock rows in multiple tables (through statements such as UPDATE or SELECT ... FOR UPDATE) in each transaction; create indexes on the columns used in SELECT ... A deadlock is a situation in which multiple ...
https://dev.mysql.com/doc/refman/8.4/en/innodb-information-schema-temp-table-info.html
mysql> SELECT * FROM INFORMATION_SCHEMA.INNODB_TEMP_TABLE_INFO\G An empty set is returned because INNODB_TEMP_TABLE_INFO and its data are not persisted to disk when the server is shut down. INNODB_TEMP_TABLE_INFO provides information about ...
https://dev.mysql.com/doc/refman/8.4/en/innodb-performance-spin_lock_polling.html
That number is generated by randomly selecting an integer ranging from 0 up to but not including the innodb_spin_wait_delay value, and multiplying that value by 50. InnoDB mutexes and rw-locks are typically reserved for short intervals. On a ...
https://dev.mysql.com/doc/refman/8.4/en/innodb-tablespace-autoextend-size.html
By default, when a file-per-table or general tablespace requires additional space, the tablespace is extended incrementally according to the following rules: If the tablespace is less than an extent in size, it is extended one page at a time. If ...
https://dev.mysql.com/doc/refman/8.4/en/innodb-temporary-tablespace.html
Issue a query similar to this one to view global temporary tablespace metadata: mysql> SELECT * FROM INFORMATION_SCHEMA.FILES WHERE TABLESPACE_NAME='innodb_temporary'\G By default, the global temporary tablespace data file is autoextending and ...
https://dev.mysql.com/doc/refman/8.4/en/invisible-indexes.html
Using the SET_VAR optimizer hint to update the value of optimizer_switch temporarily, you can enable invisible indexes for the duration of a single query only, like this: mysql> EXPLAIN SELECT /*+ SET_VAR(optimizer_switch = ... MySQL supports ...