ANALYZE FORMAT=JSON output now includes table.r_engine_stats which
has the engine statistics. Only non-zero members are printed.
Internally: EXPLAIN data structures Explain_table_acccess and
Explain_update now have handler* handler_for_stats pointer.
It is used to read statistics from handler_for_stats->handler_stats.
The following applies only to 10.9+, backport doesn't use it:
Explain data structures exist after the tables are closed. We avoid
walking invalid pointers using this:
- SQL layer calls Explain_query::notify_tables_are_closed() before
closing tables.
- After that call, printing of JSON output is disabled. Non-JSON output
can be printed but we don't access handler_for_stats when doing that.
After MDEV-30830 has added block-nl-join.r_unpack_time_ms, it became
apparent that there is some unaccounted-for time in BNL join operation,
namely the time that is spent after unpacking the join buffer record.
Fix this by adding a Gap_time_tracker to track the time that is spent
after unpacking the join buffer record and before any next time tracking.
The collected time is printed in block-nl-join.r_other_time_ms.
Reviewed by: Monty <monty@mariadb.org>
In block-nl-join, add:
- r_loops - this shows how many incoming record combinations this
query plan node had.
- r_effective_rows - this shows the average number of matching rows
that this table had for each incoming record combination. This is
comparable with r_rows in non-blocked access methods.
For BNL-joins, it is always equal to
$.table.r_rows * $.table.r_filtered
For BNL-H joins the value cannot be computed from other values
Reviewed by: Monty <monty@mariadb.org>
MDEV-27036: repeated "table" key resolve for print_explain_json
MDEV-27036: duplicated keys in best_access_path
MDEV-27036: Explain_aggr_filesort::print_json_members: resolve duplicated "filesort" member in Json object
MDEV-27036: Explain_basic_join::
print_explain_json_interns fixed start_dups_weedout case for main.explain_json test
sprintf() format of double changed from '%lg' to '%-.11lg'
The change was to make it easier to read optimizer trace output
with tables that has millions of records.
Count the "gap" time between table accesses and display it as
r_other_time_ms in the "table" element.
* The advantage of this approach is that it doesn't add any new
my_timer_cycles() calls.
* The disadvantage is that the definition of what is done during
"other time" is not that clear: it includes checking the WHERE
(for this table), constructing index lookup tuple (for the next table)
writing to GROUP BY temporary table (as we dont account for that time
separately [yet], etc)
This patch contains a full implementation of the optimization
that allows to use in-memory rowid / primary filters built for range
conditions over indexes. In many cases usage of such filters reduce
the number of disk seeks spent for fetching table rows.
In this implementation the choice of what possible filter to be applied
(if any) is made purely on cost-based considerations.
This implementation re-achitectured the partial implementation of
the feature pushed by Galina Shalygina in the commit
8d5a11122c.
Besides this patch contains a better implementation of the generic
handler function handler::multi_range_read_info_const() that
takes into account gaps between ranges when calculating the cost of
range index scans. It also contains some corrections of the
implementation of the handler function records_in_range() for MyISAM.
This patch supports the feature for InnoDB and MyISAM.
