Wikimedia\Rdbms\LoadBalancer::reuseConnection: got DBConnRef instance.
Closed, ResolvedPublicPRODUCTION ERROR
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Authored By

	• mmodell
	May 11 2017, 1:31 AM

Description

This is getting logged at a rate of 92,000 per hour, currently, and that's just group 0+1 wikis.

Stack:

#0 /srv/mediawiki/php-1.30.0-wmf.1/includes/libs/rdbms/connectionmanager/ConnectionManager.php(109): Wikimedia\Rdbms\LoadBalancer->reuseConnection() 
#1 /srv/mediawiki/php-1.30.0-wmf.1/extensions/Cognate/src/CognateStore.php(177): Wikimedia\Rdbms\ConnectionManager->releaseConnection() 
#2 /srv/mediawiki/php-1.30.0-wmf.1/extensions/Cognate/src/CognateRepo.php(138): Cognate\CognateStore->selectLinkDetailsForPage() 
#3 /srv/mediawiki/php-1.30.0-wmf.1/extensions/Cognate/src/hooks/CognateParseHookHandler.php(81): Cognate\CognateRepo->getLinksForPage() 
#4 /srv/mediawiki/php-1.30.0-wmf.1/extensions/Cognate/src/CognateHooks.php(76): Cognate\CognateParseHookHandler->doContentAlterParserOutput() 
#5 /srv/mediawiki/php-1.30.0-wmf.1/includes/Hooks.php(186): Cognate\CognateHooks::onContentAlterParserOutput()
#6 /srv/mediawiki/php-1.30.0-wmf.1/includes/content/AbstractContent.php(501): Hooks::run() 
#7 /srv/mediawiki/php-1.30.0-wmf.1/includes/poolcounter/PoolWorkArticleView.php(140): AbstractContent->getParserOutput()
#8 /srv/mediawiki/php-1.30.0-wmf.1/includes/poolcounter/PoolCounterWork.php(123): PoolWorkArticleView->doWork() 
#9 /srv/mediawiki/php-1.30.0-wmf.1/includes/page/WikiPage.php(1076): PoolCounterWork->execute() 
#10 /srv/mediawiki/php-1.30.0-wmf.1/includes/api/ApiParse.php(510): WikiPage->getParserOutput()
#11 /srv/mediawiki/php-1.30.0-wmf.1/includes/api/ApiParse.php(190): ApiParse->getParsedContent()
#12 /srv/mediawiki/php-1.30.0-wmf.1/includes/api/ApiMain.php(1578): ApiParse->execute() 
#13 /srv/mediawiki/php-1.30.0-wmf.1/includes/api/ApiMain.php(545): ApiMain->executeAction() 
#14 /srv/mediawiki/php-1.30.0-wmf.1/includes/api/ApiMain.php(516): ApiMain->executeActionWithErrorHandling() 
#15 /srv/mediawiki/php-1.30.0-wmf.1/api.php(83): ApiMain->execute() 
#16 /srv/mediawiki/w/api.php(3): include() 
#17 {main}

The error is fired by LoadBalancer->reuseConnection() in LoadBalancer.php and the culprit is rECOG23e888af1af9: Release connections as early as possible in CognateStore

Details

	Subject	Repo	Branch	Lines +/-
	Don't pass ConnectionRefs to ConnectionManager::releaseConnection	mediawiki/extensions/Cognate	wmf/1.30.0-wmf.1	+3 -3
	Don't pass ConnectionRefs to ConnectionManager::releaseConnection	mediawiki/extensions/Cognate	master	+3 -3

Customize query in gerrit

Revisions and Commits

rECOG extension-Cognate
	Audited	rECOG23e888af1af9 Release connections as early as possible in CognateStore

Related Objects
Search...

		Status	Subtype	Assigned	Task
		Resolved		• mmodell	T162954 MW-1.30.0-wmf.1 deployment blockers
		Resolved	PRODUCTION ERROR	Addshore	T165005 Wikimedia\Rdbms\LoadBalancer::reuseConnection: got DBConnRef instance.

Event Timeline

• mmodell created this task.May 11 2017, 1:31 AM

Restricted Application added a subscriber: Aklapper. · View Herald TranscriptMay 11 2017, 1:31 AM

• mmodell triaged this task as High priority.May 11 2017, 1:32 AM

• mmodell mentioned this in rECOG23e888af1af9: Release connections as early as possible in CognateStore.

• mmodell added a parent task: T162954: MW-1.30.0-wmf.1 deployment blockers.

• mmodell added a commit: rECOG23e888af1af9: Release connections as early as possible in CognateStore.

It seems either:

23e888af1af9 didn't change anything because the connections were already using references to auto-release at the end of the function.
or; 23e888af1af9 intended to release them earlier (within the same method) but should've replaced the refs with unwrapped DB objects - call getReadConnection() instead of getReadConnectionRef() and same for Write.

Unless this is a particularly slow method that is expected to run for a long time in a maintenance script or post-shutdown update or something, it probably makes more sense to assume 1 and revert the commit as being based on the assumption that it wasn't using references, which it actually was already.

Addshore claimed this task.May 11 2017, 8:02 AM

Restricted Application added a project: User-Addshore. · View Herald TranscriptMay 11 2017, 8:02 AM

This patch was made as a result of T164407 and making Cognate hold onto connections for as little time as possible.

In T165005#3253991, @Krinkle wrote:

23e888af1af9 didn't change anything because the connections were already using references to auto-release at the end of the function.

The change to CognateStore::insertPage() does change something. This releases the read connection before doing the write.

DBConnRef implements IDatabase and both ConnectionManager::releaseConnection and ILoadBalancer::reuseConnectionn are documents as accepting IDatabase, although looking into the implementation of Loadbalancer::reuseConnection it is clear it does not like DBConnRefs.
I would have expected the LB to actually handle this just fine.

Will change CognateStore to use regular connections rather than refs so that it can choose when to mark them for reuse.
And I'll probably write a patch adding some docs to the reuse and release methods here.

Change 353248 had a related patch set uploaded (by Addshore; owner: Addshore):
[mediawiki/extensions/Cognate@master] Don't pass ConnectionRefs to ConnectionManager::releaseConnection

https://gerrit.wikimedia.org/r/353248

Change 353249 had a related patch set uploaded (by Addshore; owner: Addshore):
[mediawiki/extensions/Cognate@wmf/1.30.0-wmf.1] Don't pass ConnectionRefs to ConnectionManager::releaseConnection

https://gerrit.wikimedia.org/r/353249

Addshore moved this task from Unsorted 💣 to Active 🚁 on the User-Addshore board.May 11 2017, 8:33 AM

Addshore mentioned this in rECOG0885a538e9f0: Don't pass ConnectionRefs to ConnectionManager::releaseConnection.May 11 2017, 8:33 AM

Addshore mentioned this in rECOG5898aecd88a2: Don't pass ConnectionRefs to ConnectionManager::releaseConnection.

Change 353248 merged by jenkins-bot:
[mediawiki/extensions/Cognate@master] Don't pass ConnectionRefs to ConnectionManager::releaseConnection

https://gerrit.wikimedia.org/r/353248

ReleaseTaggerBot added a project: MW-1.30-release-notes (WMF-deploy-2017-05-23_(1.30.0-wmf.2)).May 11 2017, 11:00 AM

Addshore mentioned this in T164407: Cognate has been disabled from WMF because it caused an outage on x1 by overtaking 10000 concurrent connections.May 11 2017, 12:57 PM

Change 353249 merged by jenkins-bot:
[mediawiki/extensions/Cognate@wmf/1.30.0-wmf.1] Don't pass ConnectionRefs to ConnectionManager::releaseConnection

https://gerrit.wikimedia.org/r/353249

Mentioned in SAL (#wikimedia-operations) [2017-05-11T13:21:19Z] <addshore@tin> Synchronized php-1.30.0-wmf.1/extensions/Cognate/src/CognateStore.php: SWAT: T165005 [[gerrit:353249|Dont pass ConnectionRefs to ConnectionManager::releaseConnection]] (duration: 00m 42s)