Search Results
https://dev.mysql.com/doc/refman/8.4/en/alter-table-problems.html
If you get a duplicate-key error when using ALTER TABLE to change the character set or collation of a character column, the cause is either that the new column collation maps two keys to the same value or that the table is corrupted. In the latter ...
https://dev.mysql.com/doc/refman/8.4/en/information-schema-innodb-cmp-table.html
The INNODB_CMP and INNODB_CMP_RESET tables provide status information on operations related to compressed InnoDB tables. The INNODB_CMP and INNODB_CMP_RESET tables have these columns: PAGE_SIZE The compressed page size in bytes. row ...COMPRESS_OPS ...
https://dev.mysql.com/doc/refman/8.4/en/information-schema-innodb-columns-table.html
For related usage information and examples, see Section 17.15.3, “InnoDB INFORMATION_SCHEMA Schema Object Tables”. The INNODB_COLUMNS table has these columns: TABLE_ID An identifier representing the table associated with the column; the same ...
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-host-cache-table.html
The host_cache_size system variable controls the size of the host cache, as well as the size of the host_cache table. Because the host_cache table exposes the contents of the host cache, it can be examined using SELECT statements. The host_cache ...
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-log-status-table.html
The log_status table provides information that enables an online backup tool to copy the required log files without locking those resources for the duration of the copy process. When the log_status table is queried, the server blocks logging and ...
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-metadata-locks-table.html
Metadata locking applies not just to tables, but also to schemas, stored programs (procedures, functions, triggers, scheduled events), tablespaces, user locks acquired with the GET_LOCK() function (see Section 14.14, “Locking Functions”), and ...
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-socket-instances-table.html
The socket_instances table provides a real-time snapshot of the active connections to the MySQL server. The table contains one row per TCP/IP or Unix socket file connection. Information available in this table provides a real-time snapshot of the ...row *************************** EVENT_NAME: wait/io/socket/sql/server_unix_socket OBJECT_INSTANCE_BEGIN: 4316619408 THREAD_ID: 1 SOCKET_ID: 16 IP: PORT: 0 STATE: ACTIVE *************************** ...
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-tp-thread-state-table.html
The tp_thread_state table has one row per thread created by the thread pool to handle connections. The tp_thread_state table has these columns: TP_GROUP_ID The thread group ID. TP_GROUP_ID and TP_THREAD_NUMBER together provide a unique key within ...PROCESS_COUNT The 10ms interval in which the statement that uses this thread is currently ...
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-wait-tables.html
These tables store wait events: events_waits_current: The current wait event for each thread. There are also summary tables that aggregate information about wait events; see Section 29.12.20.1, “Wait Event Summary Tables”. For more information ... The Performance Schema instruments waits, which are events that take ...
https://dev.mysql.com/doc/refman/8.4/en/repair-table-optimization.html
REPAIR TABLE for MyISAM tables is similar to using myisamchk for repair operations, and some of the same performance optimizations apply: myisamchk has variables that control memory allocation. For REPAIR TABLE, the same principle applies, but ...