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https://dev.mysql.com/doc/refman/8.4/en/charset-mysql.html
To display the available character sets, use the INFORMATION_SCHEMA CHARACTER_SETS table or the SHOW CHARACTER SET statement. To list the display collations for a character set, use the INFORMATION_SCHEMA COLLATIONS table or the SHOW COLLATION ...
https://dev.mysql.com/doc/refman/8.4/en/charset-unicode.html
MySQL 8.4 also displays utf8mb3 in place of utf8 in the columns of Information Schema tables, and in the output of SQL SHOW statements. Table 12.2, “Unicode Character Set General Characteristics”, summarizes the general characteristics of ...
https://dev.mysql.com/doc/refman/8.4/en/comparisons-using-subqueries.html
It finds all rows in table t1 containing a value that occurs twice in a given column: SELECT * FROM t1 AS t WHERE 2 = (SELECT COUNT(*) FROM t1 WHERE t1.id = t.id); For a comparison of the subquery to a scalar, the subquery must return a scalar. The ...
https://dev.mysql.com/doc/refman/8.4/en/dynamic-system-variables.html
For a description of the privilege requirements for setting system variables, see Section 7.1.9.1, “System Variable Privileges” The following table lists all dynamic system variables applicable within mysqld. This differs from the ENUM data type ... Many server system variables are dynamic and can be set at ...
https://dev.mysql.com/doc/refman/8.4/en/group-replication-configuring-consistency-guarantees.html
Although the Transaction Synchronization Points section explains that conceptually there are two synchronization points from which you can choose: on read or on write, these terms were a simplification and the terms used in Group Replication are: ...
https://dev.mysql.com/doc/refman/8.4/en/group-replication-server-states.html
The Performance Schema table replication_group_members shows the state for each member in a group. If you see this status for other servers, it can also mean that the member where you query this table is part of a partition, where a subset of the ...
https://dev.mysql.com/doc/refman/8.4/en/index-btree-hash.html
One circumstance under which this occurs is when the optimizer estimates that using the index would require MySQL to access a very large percentage of the rows in the table. (In this case, a table scan is likely to be much faster because it requires ... Understanding the B-tree and hash data structures can help predict how different queries perform on different storage engines that use these data structures in their indexes, particularly for the MEMORY storage engine that lets you choose B-tree or hash ...
https://dev.mysql.com/doc/refman/8.4/en/innodb-buffer-pool-in-core-file.html
The following table shows configuration and MADV_DONTDUMP support scenarios that determine whether core files are generated and whether they include buffer pool pages. The following table provides size reduction examples that you might see for a 1GB ... A core file records the status and memory image of a running ...
https://dev.mysql.com/doc/refman/8.4/en/innodb-deadlock-detection.html
InnoDB is aware of table locks if innodb_table_locks = 1 (the default) and autocommit = 0, and the MySQL layer above it knows about row-level locks. Otherwise, InnoDB cannot detect deadlocks where a table lock set by a MySQL LOCK TABLES statement or ... When deadlock detection is enabled (the default), InnoDB automatically detects transaction deadlocks and rolls back a transaction or transactions to break the ...
https://dev.mysql.com/doc/refman/8.4/en/innodb-disk-management.html
This section discusses the main considerations for I/O and disk space with the default kind of MySQL tables (also known as InnoDB tables): Controlling the amount of background I/O used to improve query performance. Organizing tables into many small ... As a DBA, you must manage disk I/O to keep the I/O subsystem from becoming saturated, and manage disk space to avoid filling up storage ...