Looking through ./core/Tracker/TableLogAction.php there seems to be the possibility, that two concurrent request with the same URL could result in duplicate entries.

Consider loadIdsAction executed in parallel on two installations with the same input. There should be a small time window, where both read the current state, create their list of items to be inserted, then insert the same item with different idactions, so that valid entries are created.

Thanks for the report, we should really fix this issue (although I'm not sure how to fix it).

If I understand correctly it doesn't make sense to have multiple rows in log_action with the same name/type combination, so adding a unique constraint to log_action for name/type or hash/type and changing insertNewIdsAction to use insert ignore or insert ... on duplicate should fix this.

Although I'm not sure about cleanup of existing data. If duplicates need to be deleted we have to cleanup log_link_visit_action with about 700,000,000 entries

Another possibility to workaround the issue of multiple Piwik instances writing data seems to be something like

INSERT INTO log_action ( name, hash, type, url_prefix )
SELECT * FROM (SELECT ?, CRC32(?), ?, ?) AS tmp
WHERE NOT EXISTS (
    SELECT name FROM log_action WHERE name = ? and type = ?
) LIMIT 1;

This statement should avoid inserting an entry with the same name and hash as an existing entry without using an UNIQUE constraint.

Please note: I was not able to test this statement (syntax or if it would fix the problem) due to time constraints ;)

@voidswitch thanks for your comments that's useful. Hopefully we get to this ticket in coming weeks as it's causing other bugs such as #4595

for a cleanup script, you can't just delete the 'duplicate' entries, you have to merge them:

select idaction,name,count(*) from piwik_log_action as action, piwik_log_link_visit_action as linker where linker.idaction_url_ref=action.idaction group by action.idaction order by name;

for each of the names which have multiple idactions:
(in my case i had upwards of 10 ids for the same url)

say i have multiple idactions: 63,90,134,213,180

update piwik_log_link_visit_action set idaction_url_ref=63 where idaction_url_ref in (90,134,213,180);

update piwik_log_link_visit_action set idaction_url=63 where idaction_url in (90,134,213,180);
delete from piwik_log_action where idaction in (90,134,213,180);

Did you solve the problem already? For my most visited page I have no transitions since 2013 👎

I select like 3500 rows with the above mentioned SQL-select statement! It's not that I can manually clean them up...

It would be really great if this were solved. We have the same problem and our databases date back to 2011.
Are there any news?

Just want to say thanks for the great work!

Thanks @voidswitch I also want to say great work to @diosmosis and the team!