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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-tp-thread-state-table.html
TIME_OF_ATTACH: Timestamp showing when the thread was attached, if attached to a connection; otherwise NULL. 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 ...
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/prepare.html
A parameter that is an output operand of any of CASE, COALESCE, IF, IFNULL, or NULLIF has the same derived type as the aggregated type of the operator's other output operands. If all output operands of any of CASE, COALESCE, IF, IFNULL, or NULLIF ...
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/proxy-users.html
Proxy User System Variables Two system variables help trace the proxy login process: proxy_user: This value is NULL if proxying is not used. If the plugin does not set this variable, its value is NULL. The plugin that authenticates a given ...
https://dev.mysql.com/doc/refman/8.4/en/replication-options-binary-log.html
Otherwise, if the table has a unique key all of whose columns are NOT NULL, then only the columns in the unique key need be logged. (If the table has neither a primary key nor a unique key without any NULL columns, then all columns must be used in ... Startup Options Used with Binary Logging System Variables Used with Binary Logging You can use the mysqld options and system variables that are described in this section to affect the operation of the binary log as well as to control which statements are written to the binary ...