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https://dev.mysql.com/doc/refman/5.7/en/estimating-performance.html
In most cases, you can estimate query performance by counting disk seeks. For small tables, you can usually find a row in one disk seek (because the index is probably cached). For bigger tables, you can estimate that, using B-tree indexes, you need ...In MySQL, an index block is usually 1,024 bytes and the data pointer is usually four ...
https://dev.mysql.com/doc/refman/5.7/en/information-schema-variables-table.html
Note The value of the show_compatibility_56 system variable affects the information available from the tables described here. For details, see the description of that variable in Section 5.1.7, “Server System Variables”. Note Information ...
https://dev.mysql.com/doc/refman/5.7/en/innodb-error-handling.html
A lock wait timeout causes InnoDB to roll back the current statement (the statement that was waiting for the lock and encountered the timeout). Both deadlocks and lock wait timeouts are normal on busy servers and it is necessary for applications to ...InnoDB sometimes rolls back only the statement that failed, other times it rolls back the entire ...
https://dev.mysql.com/doc/refman/5.7/en/myisam-check.html
It first checks all index entries for errors and then reads through all rows. It calculates a checksum for all key values in the rows and verifies that the checksum matches the checksum for the keys in the index tree. It does a check-read of every ... To check a MyISAM table, use the following commands: myisamchk tbl_name This finds 99.99% of all ...
https://dev.mysql.com/doc/refman/5.7/en/mysql-cluster-programs-ndb-perror.html
ndb_perror shows information about an NDB error, given its error code. Added to the MySQL NDB Cluster distribution in NDB 7.6, it is intended as a drop-in replacement for perror --ndb. To make substitution easier in scripts and other applications ...This includes the error message, the type of error, and whether the error is permanent or ...
https://dev.mysql.com/doc/refman/5.7/en/partitioning-columns.html
All of these columns are taken into account both for the purpose of placing rows in partitions and for the determination of which partitions are to be checked for matching rows in partition pruning. In addition, both RANGE COLUMNS partitioning and ... The next two sections discuss COLUMNS partitioning, which are variants on RANGE and LIST ...
https://dev.mysql.com/doc/refman/5.7/en/partitioning-limitations-functions.html
The value returned by the EXTRACT() function, when used as EXTRACT(WEEK FROM col), depends on the value of the default_week_format system variable. For this reason, EXTRACT() is not permitted as a partitioning function when it specifies the unit as ... This section discusses limitations in MySQL Partitioning relating specifically to functions used in partitioning ...
https://dev.mysql.com/doc/refman/5.7/en/performance-schema-atom-molecule-events.html
For a table I/O event, there are usually two rows in events_waits_current, not one. For example, a row fetch might result in rows like this: Row# EVENT_NAME TIMER_START TIMER_END ---- ---------- ----------- --------- 1 wait/io/file/myisam/dfile ...
https://dev.mysql.com/doc/refman/5.7/en/performance-schema-replication-applier-status-by-coordinator-table.html
For a multithreaded replica, the replica uses multiple worker threads and a coordinator thread to manage them, and this table shows the status of the coordinator thread. For a multithreaded replica, the replication_applier_status_by_worker table ...
https://dev.mysql.com/doc/refman/5.7/en/performance-schema-setup-tables.html
The setup tables provide information about the current instrumentation and enable the monitoring configuration to be changed. The use of tables rather than individual variables for setup information provides a high degree of flexibility in ...For ...