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https://dev.mysql.com/doc/refman/8.4/en/mysqldumpslow.html
The MySQL slow query log contains information about queries that take a long time to execute (see Section 7.4.5, “The Slow Query Log”). mysqldumpslow parses MySQL slow query log files and summarizes their contents. Normally, mysqldumpslow ...
https://dev.mysql.com/doc/refman/8.4/en/network-namespace-support.html
A connection may produce a result like this: $> mysql --user=admin --host=203.0.113.10 --protocol=tcp mysql> SELECT USER(); +--------------------+ | USER() | +--------------------+ | admin@198.51.100.2 | +--------------------+ In this case, the ...
https://dev.mysql.com/doc/refman/8.4/en/no-matching-rows.html
Select only those columns that are used in the WHERE clause. Issue a SELECT for the column that should have matched a row against the table that was last removed from the query. Open the file in an editor, remove some insert lines (if there are more ... If you have a complicated query that uses many tables but that returns no rows, you should use the following procedure to find out what is wrong: Test the query with EXPLAIN to check whether you can find something that is obviously ...
https://dev.mysql.com/doc/refman/8.4/en/option-defaults-equals.html
mysql> SELECT USER(); +---------------+ | USER() | +---------------+ | jon@localhost | +---------------+ 1 row in set (0.00 sec) This is not the same behavior as with the command line, where the equal sign is not required: $> mysql --user jon --host ...Due to this behavior, problems can occasionally arise when no value is provided for an option that expects ...
https://dev.mysql.com/doc/refman/8.4/en/partitioning-limitations-storage-engines.html
In MySQL 8.4, partitioning support is not actually provided by the MySQL Server, but rather by a table storage engine's own or native partitioning handler. In MySQL 8.4, only the InnoDB and NDB storage engines provide native partitioning handlers.
https://dev.mysql.com/doc/refman/8.4/en/partitioning-limitations.html
This section discusses current restrictions and limitations on MySQL partitioning support. The following constructs are not permitted in partitioning expressions: Stored procedures, stored functions, loadable functions, or plugins. For a list of ...
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-examples.html
You can determine what the thread is waiting for: SELECT * FROM performance_schema.events_waits_current WHERE THREAD_ID = thread_1; Say the query result identifies that the thread is waiting for mutex A, found in ... The Performance Schema is a tool ...
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-filtering-names.html
For example, to select all file I/O instruments, it is better to use a pattern that includes the entire instrument name prefix: ... To check which instrument or consumer names a pattern matches, perform a simple test: SELECT NAME FROM ... Names ...
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-obtaining-parent-events.html
The following scenario illustrates how to find the parent transaction of a statement in which a lock was taken: Session A: [1] START TRANSACTION; [2] SELECT * FROM t1 WHERE pk = 1; [3] SELECT 'Hello, world'; Session B: SELECT ... Rows of this table ...
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-queries.html
By contrast, post-filtering is performed by individual users through the use of queries with appropriate WHERE clauses that restrict what event information to select from the events available after pre-filtering has been applied. Pre-filtering ...