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)

vs

 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

• Shut down apache to stop tracking - or set in the config file:

[Tracker] 
record_statistics           = 0

• Run the following query to set the correct INDEXes

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 [4204]) Fixes #2220

• Dropping unused INDEX index_idsite_idvisit (the primary key will do just as good, no need for this INDEX)
• Dropping bad INDEX & adding proper one, as per discussion in ticket

@matt: yes, the performance is still excellent with cpu load around 0.3 oder 0.4. Thank you very much for this quick fix