Added Query_time (total time spent running queries) to status_variables.
Other things:
- Added SHOW_MICROSECOND_STATUS type that shows an ulonglong variable
in microseconds converted to a double (in seconds).
- Changed Busy_time and Cpu_time to use SHOW_MICROSECOND_STATUS, which
simplified the code and avoids some double divisions for each query.
Reviewed-by: Sergei Golubchik <serg@mariadb.org>
This patch allows to use semi-join optimization at the top level of
single-table update and delete statements.
The problem of supporting such optimization became easy to resolve after
processing a single-table update/delete statement started using JOIN
structure. This allowed to use JOIN::prepare() not only for multi-table
updates/deletes but for single-table ones as well. This was done in the
patch for mdev-28883:
Re-design the upper level of handling UPDATE and DELETE statements.
Note that JOIN::prepare() detects all subqueries that can be considered
as candidates for semi-join optimization. The code added by this patch
looks for such candidates at the top level and if such candidates are found
in the processed single-table update/delete the statement is handled in
the same way as a multi-table update/delete.
Approved by Oleksandr Byelkin <sanja@mariadb.com>
