We are using piwik for a quite large installation (2.5 - 3 million visitors per month). Since the update to 1.2 we have severe problems with the performance. The problem seems to be a select statement. Here is an example from our slow query log:
# Query_time: 3 Lock_time: 0 Rows_sent: 0 Rows_examined: 99728 SELECT [...] FROM piwik_log_visit WHERE visit_last_action_time >= '2011-03-21 22:01:07' AND idsite = '1' AND config_id = '...' ORDER BY visit_last_action_time DESC LIMIT 1;
The problems seems to be that about 100k rows have to be examined to find a single row, though indexes are properly set and used.
To keep performance impact low, we are currently moving data from log_visitor which is older than yesterday to an archive table. At the moment we have about 250.000 entries in the table. Before the archiving, we hav 20 million with tracking started in april 2009.
a first info I would be interested in is if it is safe to move data to an archive table or if it affects the accuracy of the reports.
Reports are affected if raw data (e.g., piwik_log_visit) is moved/purged before archives have been generated for the period (e.g., unique visitors for the past month or week).
Are there a lot of config_id collisions?
Is order important in the index? e.g.,
INDEX index_idsite_datetime_config (idsite, visit_last_action_time, config_id)
INDEX index_idsite_config_datetime (idsite, config_id, visit_last_action_time)
To answer my own question, yes, order of columns is important in the index. http://dev.mysql.com/doc/refman/5.0/en/mysql-indexes.html
We'll add the latter index (above), and see if there other queries that depend on the former index. (If not, we can remove that one.)
It looks like the archiving queries benefit from the former index, but can probably be simplified by removing the config_id column. So index_idsite_datetime_config would be replaced by these indexes:
INDEX index_idsite_datetime (idsite, visit_last_action_time) INDEX index_idsite_config_datetime (idsite, config_id, visit_last_action_time)
vipsoft I think the same as #2220
indeed order is very important in INDEXes, sorry I missed this issue with new schema in 1.2...
pdfforge, would be able to test these INDEXes by any chance? It would be great to test on your high traffic Piwik the following
[Tracker] record_statistics = 0
ALTER TABLE piwik_log_visit DROP INDEX index_idsite_datetime_config, ADD INDEX index_idsite_config_datetime (idsite, config_id, visit_last_action_time), ADD INDEX index_idsite_datetime (idsite, visit_last_action_time)
I think this should fix the issue.
However it is still not ideal since the INDEX index_idsite_config_datetime will be rather large, but this will not be an issue once we can implement log purge #5
pddfforge, please let us know if you can test these changes, thanks!
It made a slight improvement. Before the update, mysql had 150% CPU-Utilization and caused a load average of 2.5. Now it is 0.7% and 0.2 util.
that's really significant... Thank you very much!
I will keep watching how it develops over the day, but it looks very good.
That looks like an idle box. Did you re-enable tracking after the index change, i.e., record_statistics=1 ?
yes, I re-enabled tracking and the cpu usage really is very low. The above query now only checks one row instead of 100k. Most of the time is now spent with the php processes.
The data also look good (100k visitors yesterday spread over the whole day in server time).
Thx for the follow up. Glad it's all working fine again!
pdfforge do you still experience very good performance since the INDEX change? there is no other problem?
(In ) Fixes #2220
@matt: yes, the performance is still excellent with cpu load around 0.3 oder 0.4. Thank you very much for this quick fix