Optimize userstat code
Converting an internal email by Alexey Stroganov to a blueprint.
I've profiled mysqld with oprofile, see below some functions re: userstat:
samples %
245479 0.4232 mysqld update_
bool, long)
233103 0.4019 mysqld get_key_index_stats
195836 0.3376 mysqld
handler:
186488 0.3215 mysqld
handler:
64076 0.1105 mysqld get_key_user_stats
62424 0.1076 mysqld get_key_table_stats
I've annotated sources and it seems that we:
- quite often use strlen:
...
58285 0.1005 : *length= strlen(
59393 0.1024 : *length= strlen(
220833 0.3807 : *length= strlen(
...
- accessing thd:
...
38274 0.0660 : user_stats-
thd->last_
43263 0.0746 : user_stats-
thd->diff_
...
Blueprint information
- Status:
- Complete
- Approver:
- Alexey Kopytov
- Priority:
- High
- Drafter:
- Alexey Stroganov
- Direction:
- Approved
- Assignee:
- Sergei Glushchenko
- Definition:
- Approved
- Series goal:
- Accepted for 5.6
- Implementation:
-
Implemented
- Milestone target:
-
5.6.15-63.0
- Started by
- Alexey Kopytov
- Completed by
- Alexey Kopytov
Related bugs
Sprints
Whiteboard
Targetting to 5.6 GA, but any work done that also applies to 5.5 should be done there too and will need creating separate blueprints/bug reports.
Sergei has questions (based on 5.5 branch):
- It's easy to get rid of that much strlen's, just to save lengths in
*_STAT structs. The whole point of this feature is to get stats from
THD and aggregte them grouped by user, thread, table, etc. I don't see
a good way how to ret rid o accessing THD. Is there one?
KAlexey> saving lengths in _STAT structs looks like a good idea. Though I'm not sure accessing THD per se has any measurable overhead. It's more likely that incrementing the _STAT structure members suffers from false sharing (since they are shared). But it needs further investigation.
- Functions add_user_stats, add_thread_stats are never used, can we just
remove them?
KAlexey> yes, this is bug #1082333.
- Condition opt_userstat in update_
become false, what is point of it's "else" branch?
KAlexey> Agree, that check is redundant.
Laurynas: the MP was merged in its current form (eliminate strlen(), couple of unused functions, one redundant if). If the THD accesses need to be addressed, this will have to be done in a new userstat benchmarking round and a follow-up blueprint.
