| Addshore added a comment. |
So the timing point that I am looking at is the selectClient call in dispatchChanges.php
$wikiState = $dispatcher->selectClient();
Which is wrapped by some code sending data to wikibase.repo.dispatchChanges.selectClient-time in graphite, which can be looked at on https://grafana.wikimedia.org/dashboard/db/wikidata-dispatch-script in combination with other metrics.
The selectClient does a couple of things, but the only a few of which would make sense to see this sort of speed change.
Two queries come from Wikibase\Store\Sql\SqlChangeDispatchCoordinator::getCandidateClients and would be something like this on an s8 replica:
SELECT max( change_id ) as maxid FROM wb_changes SELECT chd_site FROM wb_changes_dispatch WHERE ........... ORDER BY chd_seen ASC LIMIT ??And from Wikibase\Store\Sql\SqlChangeDispatchCoordinator::lockClient also on an s8 replica:
SELECT chd_site,chd_db,chd_seen,chd_touched,chd_lock,chd_disabled FROM wb_changes_dispatch WHERE chd_site = ????The method also interacts with redis creating locks with the following key:
Wikibase.{$this->repoSiteId}.dispatchChanges.$siteID
Cc: User-Marostegui, Banyek, jcrespo, Marostegui, Addshore, Aklapper, Nandana, jijiki, Lahi, Gq86, GoranSMilovanovic, QZanden, LawExplorer, Volans, Wikidata-bugs, aude, Mbch331, Krenair, akosiaris
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