Search Results
https://dev.mysql.com/doc/refman/8.4/en/error-log.html
The error log contains a record of mysqld startup and shutdown times. This section discusses how to configure the MySQL server for logging of diagnostic messages to the error log. For example, if mysqld notices that a table needs to be ...For ...
https://dev.mysql.com/doc/refman/8.4/en/explain-for-connection.html
For example, if you are running a statement in one session that is taking a long time to complete, using EXPLAIN FOR CONNECTION in another session may yield useful information about the cause of the delay. To obtain the execution plan for an ...
https://dev.mysql.com/doc/refman/8.4/en/external-locking.html
External locking is used in situations where a single process such as the MySQL server cannot be assumed to be the only process that requires access to tables. If the server is run with external locking enabled, you can use myisamchk at any time for ... External locking is the use of file system locking to manage contention for MyISAM database tables by multiple ...
https://dev.mysql.com/doc/refman/8.4/en/function-optimization.html
MySQL also determines when to evaluate functions based on types of arguments, whether the arguments are table columns or constant values. For example: SELECT * FROM t WHERE partial_key=5 AND some_column=RAND(); If the optimizer can use partial_key ...A function is nondeterministic if, given fixed values for its arguments, it can return different results for different ...
https://dev.mysql.com/doc/refman/8.4/en/group-replication-tuning-recovery.html
The following statement sets the maximum number of attempts to connect to a donor to 5: mysql> SET GLOBAL group_replication_recovery_retry_count= 5; For remote cloning operations, this limit does not apply. Sleep Interval for Connection Attempts For ... Several aspects of Group Replication's distributed recovery process can be configured to suit your ...
https://dev.mysql.com/doc/refman/8.4/en/information-schema-innodb-buffer-page-table.html
ACCESS_TIME An abstract number used to judge the first access time of the page. The INNODB_BUFFER_PAGE table provides information about each page in the InnoDB buffer pool. For related usage information and examples, see Section 17.15.5, “InnoDB ...
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-enabling-monitors.html
When InnoDB monitors are enabled for periodic output, InnoDB writes the output to mysqld server standard error output (stderr) every 15 seconds, approximately. InnoDB monitor output begins with a header containing a timestamp and the monitor name.
https://dev.mysql.com/doc/refman/8.4/en/innodb-file-defragmenting.html
Another symptom of fragmentation is that a table scan such as this takes more time than it “should” take: SELECT COUNT(*) FROM t WHERE non_indexed_column <> 12345; The preceding query requires MySQL to perform a full table scan, the slowest type ...To speed up index scans, you can periodically perform a “null” ALTER TABLE operation, which causes MySQL to rebuild the table: ALTER TABLE tbl_name ENGINE=INNODB You can also use ALTER TABLE tbl_name FORCE to perform a “null” alter operation that rebuilds the ...
https://dev.mysql.com/doc/refman/8.4/en/innodb-online-ddl-failure-conditions.html
A timeout occurs while waiting for an exclusive lock on the table, which may be needed briefly during the initial and final phases of the DDL operation. The tmpdir or innodb_tmpdir file system runs out of disk space, while MySQL writes temporary ...