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https://dev.mysql.com/doc/refman/5.7/en/performance-schema-mutex-instances-table.html
LOCKED_BY_THREAD_ID When a thread currently has a mutex locked, LOCKED_BY_THREAD_ID is the THREAD_ID of the locking thread, otherwise it is NULL. When a thread unlocks a mutex, mutex_instances shows that the mutex now has no owner (the THREAD_ID ...
https://dev.mysql.com/doc/refman/5.7/en/performance-schema-performance-timers-table.html
The rows that do not contain NULL indicate which timers you can use in setup_timers. For an explanation of how event timing occurs, see Section 25.4.1, “Performance Schema Event Timing”. Note As of MySQL 5.7.21, the Performance Schema ...
https://dev.mysql.com/doc/refman/5.7/en/performance-schema-stage-tables.html
The Performance Schema instruments stages, which are steps during the statement-execution process, such as parsing a statement, opening a table, or performing a filesort operation. Stages correspond to the thread states displayed by SHOW ...
https://dev.mysql.com/doc/refman/5.7/en/performance-schema-table-wait-summary-tables.html
A value of NULL means that table I/O used no index. The following sections describe the table I/O and lock wait summary tables: table_io_waits_summary_by_index_usage: Table I/O waits per index table_io_waits_summary_by_table: Table I/O waits per ...
https://dev.mysql.com/doc/refman/5.7/en/primary-key-optimization.html
Query performance benefits from the NOT NULL optimization, because it cannot include any NULL values. The primary key for a table represents the column or set of columns that you use in your most vital queries. With the InnoDB storage engine, the ...
https://dev.mysql.com/doc/refman/5.7/en/processlist-access.html
db is the default database for the thread, or NULL if none has been selected. Info indicates the statement the thread is executing, or NULL if it is executing no statement. The following discussion enumerates the sources of process information, the ...
https://dev.mysql.com/doc/refman/5.7/en/regexp.html
If either expr or pat is NULL, the return value is NULL. Table 12.14 Regular Expression Functions and Operators Name Description NOT REGEXP Negation of REGEXP REGEXP Whether string matches regular expression RLIKE Whether string matches regular ...
https://dev.mysql.com/doc/refman/5.7/en/replication-administration-status.html
row *************************** Id: 10 User: root Host: replica1:58371 db: NULL Command: Binlog Dump Time: 777 State: Has sent all binlog to slave; waiting for binlog to be updated Info: NULL Because it is the replica that drives the replication ...
https://dev.mysql.com/doc/refman/5.7/en/rewriter-query-rewrite-plugin-reference.html
If no error occurs when the rules table is loaded into memory, the plugin sets the message column to NULL. A non-NULL value indicates an error and the column contents are the error message. Users communicate with the plugin by modifying the set of ...
https://dev.mysql.com/doc/refman/5.7/en/sys-diagnostics.html
Use NULL to collect data for the default of 60 seconds. Creates a report of the current server status for diagnostic purposes. This procedure disables binary logging during its execution by manipulating the session value of the sql_log_bin system ...