Retrieving the change log for a contact takes ages for my client - maybe a response of 10 minutes to get just 79 records for one contact. The contact database has about 39K rows, but with about 950k rows in the civicrm_log table (there are lots of transactions). Logging is switched on, which at the time seemed a very attractive option.

Would adding an index help? I have defragged & optimised the civicrm_log table, but to no effect.

6 Answers 6


If logging is on then results will be retrieved from the log_xxx tables not civicm_log.

Normally these tables use the archive engine - which is not indexable. We have in some cases selectively converted these to INNODB & added indexes

Archive tables are supposed to be quick to write to and slow to read from. They are also non-transactional - which means that if a rollback happens for a given transaction the archive table record will not be rolled back (on rare occasions this has helped us with forensics)

EDIT: also take a look at this extension I wrote https://github.com/eileenmcnaughton/nz.co.fuzion.innodbtriggers which converts log tables to innodb automatically and this blog post for more details: https://civicrm.org/blog/eileen/who-did-what-when


For people googling, I significantly increased the speed of the Change Log by following Eileen's advice in her answer: convert some tables (activity, activity_contact, contact, group, group_contact) from ARCHIVE to INNODB, and adding indexes.

The Change Log still takes ~20 seconds to load, but that's much better than the minutes it used to. We've taken a hit on disk space, and I suppose write speed (though I can't tell the difference), but definitely worth it!


The log tables as originally implemented (I have checked for a few years if this is the case) also contain a large number of superfluous records due to writes that don't actually change the data. Improving the triggers to check for a difference between old and new values before the write to log would improve things for everyone.


Take a look at the INNODB logging extension. It converts the log table format from ARCHIVE to INNODB, adding indexes and speeding up as a result.


Pretty sure an index would help indeed, the question is which one?

Can you log slow queries on your database and see which queries are taking a lot of time, see where it can be added?

finetune how many seconds before a query is slow (any query that takes more than 1 or 2 sec is slow is what I use)


  • Thanks - I know how to reproduce the problem - just click on 'Change Log' tab in the summary screen for almost anyone. I just tried this for someone who has maybe only a very few transactions, and it's still running. So how do I find out which SQL query is running? Or, as you said, how do I log slow queries?
    – Andy Clark
    Commented Nov 13, 2015 at 8:35
  • added a link to mysql doc on slow query log
    – Xavier
    Commented Nov 13, 2015 at 9:12
  • Here's an example. Clicking on the Change Log was triggering this sql: SELECT group_id FROM log_civicrm_group_contact WHERE log_date <= 20180828. Since that table has 2 million + records and it's an ARCHIVE without an index, it's bound to be slow. Other times, it seemed to be spending time sorting the results, so I suspect if you just add indices to the log_date timestamp field for all your big log_* tables, it might fix 90% of the issue.
    – Alan Dixon
    Commented Oct 19, 2018 at 15:45

I discussed this with Bjorn Endres, and his idea is to turn logging off, drop the log tables, and then turn logging back on. This is, I think, a good answer. The reason our log tables are so big is because we have transferred data from a legacy system. We don't really need 99% of the data in these logs so this is what we intend to do. Thanks, Bjorn!

  • I've got detailed logging turned on for a couple of current sites I'm working with, and these are set up to use a separate database (not the main civicrm db). Don't know if this might help?
    – Graham
    Commented Nov 18, 2015 at 12:48
  • That's interesting, Graham. I guess this involved changes in Civi? What were they?
    – Andy Clark
    Commented Nov 19, 2015 at 13:13
  • @andy-clarke If you look in the civicrm.settings.php file you'll see there is an option there to define a separate db for logging.
    – Graham
    Commented Nov 20, 2015 at 10:32

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