For all degenerate select queries having sub-queries in them,
the field rows_examined in the slow query log is always being set to 0.
The problem is that, although sub-queries increment the rows_examined field
of the thd object correctly, the degenerate outer select query is resetting
the rows_examined to zero after it has finished execution, by
invoking thd->set_examined_row_count(0).
The solution is to remove the thd->set_examined_row_count(0) in the
degenerate select queries.
For all "UNION ALL" queries, the field rows_examined in the
slow query log is always being set to 0. However, this is not
the case with UNION queries although both UNION, and UNION ALL
share the same code.
The problem is that for UNION ALL queries, rows_examined field
in the thd object is not updated to the actual processed rows,
although they are being tracked in the sql_union.cc
Later, when the thd object is used to dump the examined rows
to the slow query log, it was only writing 0, as thd object was
never updated with the processed rows count.
This PR addresses the concern to write rows_examined field correctly
for UNION_ALL queries to the slow query log.
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>
