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https://dev.mysql.com/doc/refman/5.7/en/gis-polygon-property-functions.html
For arguments of dimension 0 or 1, the result is 0. The result is the sum of the area values of all components for a geometry collection. ST_Centroid({poly|mpoly}) Returns the mathematical centroid for the Polygon or MultiPolygon argument as a Point. This function processes geometry collections by computing the centroid point for components of highest dimension in the ...
https://dev.mysql.com/doc/refman/5.7/en/mysql-cluster-config-send-buffers.html
This parameter can be set for all types of NDB Cluster nodes—that is, it can be set in the [ndbd], [mgm], and [api] (or [mysql]) sections of the config.ini file. It represents the total amount of memory (in bytes) to be allocated by each node for ...Configuration of the unified send buffer can accomplished by setting the following parameters: ... The NDB kernel ...
https://dev.mysql.com/doc/refman/5.7/en/miscellaneous-optimization-tips.html
This section lists a number of miscellaneous tips for improving query processing speed: If your application makes several database requests to perform related updates, combining the statements into a stored routine can help performance. In this ...
https://dev.mysql.com/doc/refman/5.7/en/optimizing-queries-myisam.html
An update of the following form is very fast: UPDATE tbl_name SET count_col=count_col+1 WHERE key_col=constant; This is very important when you use MySQL storage engines such as MyISAM that has only table-level locking (multiple readers with single ... Some general tips for speeding up queries on MyISAM tables: To help MySQL better optimize queries, use ANALYZE TABLE or run myisamchk --analyze on a table after it has been loaded with ...
https://dev.mysql.com/doc/refman/5.7/en/tracing-example.html
Now we can examine the trace, whose first column (QUERY), containing the original statement to be traced, is shown here: SELECT * FROM INFORMATION_SCHEMA.OPTIMIZER_TRACE\G *************************** 1. Next, for every table in the query, we ...row ...
https://dev.mysql.com/doc/refman/5.7/en/checksum-table.html
[QUICK | EXTENDED] CHECKSUM TABLE reports a checksum for the contents of a table. You can use this statement to verify that the contents are the same before and after a backup, rollback, or other operation that is intended to put the data back to a ...If you run CHECKSUM TABLE against a view, the Checksum value is always NULL, and a warning is ...
https://dev.mysql.com/doc/refman/5.7/en/innodb-information-schema-understanding-innodb-locking.html
When a transaction updates a row in a table, or locks it with SELECT FOR UPDATE, InnoDB establishes a list or queue of locks on that row. Similarly, InnoDB maintains a list of locks on a table for table-level locks. If a second transaction wants to ...At any given time, a transaction may request a lock that is held by another transaction, in which case it is blocked by that other ...
https://dev.mysql.com/doc/refman/5.7/en/performance-schema-socket-summary-tables.html
Except for events_statements_summary_by_digest, tt resets the summary columns to zero rather than removing rows. These socket summary tables aggregate timer and byte count information for socket operations: socket_summary_by_event_name: Aggregate ...When a connection terminates, the row in socket_summary_by_instance corresponding to it is ...
https://dev.mysql.com/doc/refman/5.7/en/show-status.html
SHOW [GLOBAL | SESSION] STATUS [LIKE 'pattern' | WHERE expr] Note The value of the show_compatibility_56 system variable affects the information available from and privileges required for the statement described here. For details, see the ...A ...
https://dev.mysql.com/doc/refman/5.7/en/sys-host-summary-by-statement-latency.html
Rows for which the HOST column in the underlying Performance Schema table is NULL are assumed to be for background threads and are reported with a host name of background. total_latency The total wait time of timed statements for the host. The ...