MySQL :: MySQL 8.0 Reference Manual

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30.4.3.41 The user_summary and x$user_summary Views

https://dev.mysql.com/doc/refman/8.0/en/sys-user-summary.html

These views summarize statement activity, file I/O, and connections, grouped by user. The user_summary and x$user_summary views have these columns: user The client user name. Rows for which the USER column in the underlying Performance Schema table ...

30.4.3.48 The wait_classes_global_by_avg_latency and x$wait_classes_global_by_avg_latency Views

https://dev.mysql.com/doc/refman/8.0/en/sys-wait-classes-global-by-avg-latency.html

These views summarize wait class average latencies, grouped by event class. An event class is determined by stripping from the event name everything after the first three components. The wait_classes_global_by_avg_latency and ...

30.4.3.49 The wait_classes_global_by_latency and x$wait_classes_global_by_latency Views

https://dev.mysql.com/doc/refman/8.0/en/sys-wait-classes-global-by-latency.html

These views summarize wait class total latencies, grouped by event class. An event class is determined by stripping from the event name everything after the first three components. The wait_classes_global_by_latency and ...

30.4.3.50 The waits_by_host_by_latency and x$waits_by_host_by_latency Views

https://dev.mysql.com/doc/refman/8.0/en/sys-waits-by-host-by-latency.html

These views summarize wait events, grouped by host and event. By default, rows are sorted by host and descending total latency. The waits_by_host_by_latency and x$waits_by_host_by_latency views have these columns: host The host from which the ...

30.4.3.51 The waits_by_user_by_latency and x$waits_by_user_by_latency Views

https://dev.mysql.com/doc/refman/8.0/en/sys-waits-by-user-by-latency.html

These views summarize wait events, grouped by user and event. By default, rows are sorted by user and descending total latency. The waits_by_user_by_latency and x$waits_by_user_by_latency views have these columns: user The user associated with the ...

30.4.3.52 The waits_global_by_latency and x$waits_global_by_latency Views

https://dev.mysql.com/doc/refman/8.0/en/sys-waits-global-by-latency.html

The waits_global_by_latency and x$waits_global_by_latency views have these columns: events The event name. total_latency The total wait time of timed occurrences of the event. avg_latency The average wait time per timed occurrence of the event.

B.3.3.5 Where MySQL Stores Temporary Files

https://dev.mysql.com/doc/refman/8.0/en/temporary-files.html

(In such cases, lsof +L1 may be helpful in identifying large files associated with mysqld.) When sorting (ORDER BY or GROUP BY), MySQL normally uses one or two temporary files. On Unix, MySQL uses the value of the TMPDIR environment variable as the ...

3.6 Preparing Your Installation for Upgrade

https://dev.mysql.com/doc/refman/8.0/en/upgrade-prerequisites.html

REORGANIZE PARTITION: ALTER TABLE table_name REORGANIZE PARTITION partition_name INTO (partition_definition TABLESPACE=innodb_file_per_table); There must be no queries and stored program definitions from MySQL 8.0.12 or lower that use ASC or DESC ...

3.4 What the MySQL Upgrade Process Upgrades

https://dev.mysql.com/doc/refman/8.0/en/upgrading-what-is-upgraded.html

Note that following an upgrade with this option, Group Replication cannot be started, because system tables on which the replication internals depend are not updated, and reduced functionality might also be apparent in other areas. Installing a new ...

11.4 User-Defined Variables

https://dev.mysql.com/doc/refman/8.0/en/user-variables.html

HAVING, GROUP BY, and ORDER BY, when referring to a variable that is assigned a value in the select expression list do not work as expected because the expression is evaluated on the client and thus can use stale column values from a previous row.

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