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https://dev.mysql.com/doc/refman/5.7/en/performance-schema-processlist-table.html
The processlist table contains a row for each server process: mysql> SELECT * FROM performance_schema.processlist\G *************************** 1. row *************************** ID: 10 USER: me HOST: localhost:58834 DB: test COMMAND: Query TIME: 0 ... Note The processlist table is automatically created in the Performance Schema for new installations of MySQL 5.7.39, or ...
https://dev.mysql.com/doc/refman/5.7/en/performance-schema-stage-tables.html
To enable the instrument and the relevant consumers, execute these statements: UPDATE performance_schema.setup_instruments SET ENABLED='YES' WHERE NAME='stage/sql/copy to tmp table'; UPDATE performance_schema.setup_consumers SET ENABLED='YES' WHERE ... 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 ...
https://dev.mysql.com/doc/refman/5.7/en/performance-schema-timing.html
For display when events are retrieved from Performance Schema tables, times are shown in picoseconds (trillionths of a second) to normalize them to a standard unit, regardless of which timer is selected. Events are collected by means of ...
https://dev.mysql.com/doc/refman/5.7/en/problems-with-null.html
All columns in the following example return NULL: mysql> SELECT NULL, 1+NULL, CONCAT('Invisible',NULL); To search for column values that are NULL, you cannot use an expr = NULL test. The following statement returns no rows, because expr = NULL is ...
https://dev.mysql.com/doc/refman/5.7/en/query-cache.html
The query cache stores the text of a SELECT statement together with the corresponding result that was sent to the client. If all the queries you are performing are simple (such as selecting a row from a table with one row), but still differ so that ... Note The query cache is deprecated as of MySQL 5.7.20, and is removed in MySQL ...
https://dev.mysql.com/doc/refman/5.7/en/replication-options-replica.html
Tell the replication SQL thread to restrict replication to statements where the default database (that is, the one selected by USE) is db_name. To specify more than one database, use this option multiple times, once for each database; however, doing ... This section explains the server options and system variables that apply to replicas and contains the following: Startup Options for Replicas Options for Logging Replica Status to Tables System Variables Used on Replicas Specify the options either on the command line or in an option ...
https://dev.mysql.com/doc/refman/5.7/en/replication-options-source.html
The highest value present in the col column prior to the INSERT is 31, and the next available value in the AUTO_INCREMENT series is 35, so the inserted values for col begin at that point and the results are as shown for the SELECT query. This ...
https://dev.mysql.com/doc/refman/5.7/en/rewriter-query-rewrite-plugin.html
These elements work together to provide SELECT rewriting capability: A server-side plugin named Rewriter examines SELECT statements and may rewrite them, based on its in-memory cache of rewrite rules. Standalone SELECT statements and SELECT ...
https://dev.mysql.com/doc/refman/5.7/en/searching-on-two-keys.html
The one tricky case is that of searching on two different keys combined with OR: SELECT field1_index, field2_index FROM test_table WHERE field1_index = '1' OR field2_index = '1' This case is optimized. You can also solve the problem efficiently by ... An OR using a single key is well optimized, as is the handling of ...
https://dev.mysql.com/doc/refman/5.7/en/server-status-variables.html
If a query result is returned from query cache, the server increments the Qcache_hits status variable, not Com_select. Connection_errors_select The number of errors that occurred during calls to select() or poll() on the listening port. If this ...