Hello,
tag_summary table was introduced in 2009 as a roll up table for change_tag.
One of the reasons it was being used was that MySQL databases that were
using earlier versions of 4.1 (Released at 15 February 2005) could not use
GROUP_CONCAT feature.
Around five years ago, developers started to replace usages of tag_summary
with change_tag primarily because GROUP_CONCAT became available then and it
most cases it was faster. For example [1] but it wasn't done fully which
led us to having discrepancies. For example, Special:RecentChanges uses
change_tag table but its API counterpart uses tag_summary table.
Maintaining two extremely large tables is a technical debt that have been
biting us since its deployment. Also, with normalization of change_tag
table in place [2], it's more performant than tag_summary.
So we are replacing usages of this table with change_tag and in the next
couple of weeks, and then we will drop the whole table. If you're using it
in cloud replicas, please change it to change_tag. If you have any concerns
or notes, feel free to chime in at
https://phabricator.wikimedia.org/T209525
(Also, review of the patches would be extremely appreciated)
Thank you and sorry for any inconvenience.
[1]:
https://gerrit.wikimedia.org/r/c/mediawiki/core/+/95584
[2]:
https://phabricator.wikimedia.org/T185355
Best
--
Amir Sarabadani
Software Engineer
Wikimedia Deutschland e. V. | Tempelhofer Ufer 23-24 | 10963 Berlin
Tel. (030) 219 158 26-0
http://wikimedia.de
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