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https://dev.mysql.com/doc/refman/8.4/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/8.4/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/8.4/en/performance-schema-tp-connections-table.html
TP_PROCESSING_THREAD_NUMBER This may be NULL if no thread is currently attached to the connection. TIME_OF_EXPIRY Timestamp showing when an idle connection will expire if no new request arrives before then; this is NULL when the thread is currently ... The tp_connections table contains one row per connection managed by the Thread Pool ...
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-user-defined-functions-table.html
The value is NULL if the function was registered by a CREATE FUNCTION statement and is in the process of unloading. The value is NULL if the function was registered by a component or plugin rather than by a CREATE FUNCTION statement. The ...
https://dev.mysql.com/doc/refman/8.4/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/8.4/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/8.4/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/8.4/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 ...
https://dev.mysql.com/doc/refman/8.4/en/sys-processlist.html
db The default database for the thread, or NULL if there is none. current_statement The statement the thread is executing, or NULL if it is not executing any statement. The MySQL process list indicates the operations currently being performed by ...
https://dev.mysql.com/doc/refman/8.4/en/sys-ps-is-consumer-enabled.html
Returns YES or NO to indicate whether a given Performance Schema consumer is enabled, or NULL if the argument is NULL. If the argument is not a valid consumer name, an error occurs. This function accounts for the consumer hierarchy, so a consumer ...