https://dev.mysql.com/subquery-materialization.html
The first time MySQL needs the subquery result, it materializes that result into a temporary table. Any subsequent time the result is needed, MySQL refers again to the temporary table. If materialization is not used, the optimizer sometimes rewrites ... The optimizer uses materialization to enable more efficient subquery ...
https://dev.mysql.com/subquery-restrictions.html
FROM t...) AS dt ...); Here the result from the derived table is materialized as a temporary table, so the relevant rows in t have already been selected by the time the update to t takes place. In MySQL, it can produce nondeterministic results ...
https://dev.mysql.com/sys-diagnostics.html
in_interval INT UNSIGNED: The sleep time between data collections in seconds. Creates a report of the current server status for diagnostic purposes. This procedure disables binary logging during its execution by manipulating the session value of ...
https://dev.mysql.com/sys-host-summary-by-file-io.html
io_latency The total wait time of timed file I/O events for the host. By default, rows are sorted by descending total file I/O latency. The host_summary_by_file_io and x$host_summary_by_file_io views have these columns: host The host from which the ...
https://dev.mysql.com/sys-user-summary-by-file-io.html
io_latency The total wait time of timed file I/O events for the user. By default, rows are sorted by descending total file I/O latency. The user_summary_by_file_io and x$user_summary_by_file_io views have these columns: user The client user name.
https://dev.mysql.com/table-handles-table.html
The Performance Schema exposes table lock information through the table_handles table to show the table locks currently in effect for each opened table handle. This information shows which table handles the server has open, how they are locked, and ...
https://dev.mysql.com/unix-signal-response.html
Clients can prevent installation of SIGPIPE handlers by specifying the CLIENT_IGNORE_SIGPIPE option to mysql_real_connect() at connect time. On Unix and Unix-like systems, a process can be the recipient of signals sent to it by root or the account ...
https://dev.mysql.com/update.html
Each matching row is updated once, even if it matches the conditions multiple times. The implicit default value is 0 for numeric types, the empty string ('') for string types, and the “zero” value for date and time types. UPDATE is a DML ...
https://dev.mysql.com/using-date.html
MySQL also permits a “relaxed” string format when updating and in a WHERE clause that compares a date to a DATE, DATETIME, or TIMESTAMP column. When you compare a DATE, TIME, DATETIME, or TIMESTAMP to a constant string with the <, <=, =, >=, >, ...You should use this format in UPDATE expressions and in the WHERE clause of SELECT ...
https://dev.mysql.com/using-gdb-on-mysqld.html
In this case, you can only have one thread active at a time. It is very hard to debug MySQL under gdb if you do a lot of new connections the whole time as gdb does not free the memory for old threads. On most systems you can also start mysqld from ...
