When trying to merge Items that are too big, the EntityContentTooBigException is not caught, but shown to the user. We should show a meaningful error message instead.
Dashboard for these errors: https://logstash.wikimedia.org/goto/7e9dcccb2761199879c6ed6fb922ab93
Error
- mwversion: 1.40.0-wmf.1
- reqId: 4cbe2973-0552-4be1-8ad9-03444ab59ae3
- Find reqId in Logstash
normalized_message
[{reqId}] {exception_url} Wikibase\Lib\Store\EntityContentTooBigException:exception.trace
from /srv/mediawiki/php-1.40.0-wmf.1/extensions/Wikibase/lib/includes/Store/EntityContentDataCodec.php(160)
#0 /srv/mediawiki/php-1.40.0-wmf.1/extensions/Wikibase/repo/includes/Content/EntityHandler.php(372): Wikibase\Lib\Store\EntityContentDataCodec->encodeEntity(Wikibase\DataModel\Entity\Item, string)
#1 /srv/mediawiki/php-1.40.0-wmf.1/includes/content/AbstractContent.php(174): Wikibase\Repo\Content\EntityHandler->serializeContent(Wikibase\Repo\Content\ItemContent, string)
#2 /srv/mediawiki/php-1.40.0-wmf.1/includes/Storage/PageEditStash.php(438): AbstractContent->serialize(string)
#3 /srv/mediawiki/php-1.40.0-wmf.1/includes/Storage/PageEditStash.php(263): MediaWiki\Storage\PageEditStash->getContentHash(Wikibase\Repo\Content\ItemContent)
#4 /srv/mediawiki/php-1.40.0-wmf.1/includes/Storage/DerivedPageDataUpdater.php(883): MediaWiki\Storage\PageEditStash->checkCache(Title, Wikibase\Repo\Content\ItemContent, User)
#5 /srv/mediawiki/php-1.40.0-wmf.1/includes/Storage/PageUpdater.php(335): MediaWiki\Storage\DerivedPageDataUpdater->prepareContent(User, MediaWiki\Storage\RevisionSlotsUpdate, boolean)
#6 /srv/mediawiki/php-1.40.0-wmf.1/includes/Storage/PageUpdater.php(890): MediaWiki\Storage\PageUpdater->prepareUpdate()
#7 /srv/mediawiki/php-1.40.0-wmf.1/extensions/Wikibase/repo/includes/Store/Sql/WikiPageEntityStore.php(410): MediaWiki\Storage\PageUpdater->saveRevision(CommentStoreComment, integer)
#8 /srv/mediawiki/php-1.40.0-wmf.1/extensions/Wikibase/repo/includes/Store/Sql/WikiPageEntityStore.php(269): Wikibase\Repo\Store\Sql\WikiPageEntityStore->saveEntityContent(Wikibase\Repo\Content\ItemContent, User, string, integer, boolean, array)
#9 /srv/mediawiki/php-1.40.0-wmf.1/extensions/Wikibase/lib/includes/Store/TypeDispatchingEntityStore.php(90): Wikibase\Repo\Store\Sql\WikiPageEntityStore->saveEntity(Wikibase\DataModel\Entity\Item, string, User, integer, boolean, array)
#10 /srv/mediawiki/php-1.40.0-wmf.1/extensions/Wikibase/repo/includes/Interactors/ItemMergeInteractor.php(297): Wikibase\Lib\Store\TypeDispatchingEntityStore->saveEntity(Wikibase\DataModel\Entity\Item, string, User, integer, boolean, array)
#11 /srv/mediawiki/php-1.40.0-wmf.1/extensions/Wikibase/repo/includes/Interactors/ItemMergeInteractor.php(275): Wikibase\Repo\Interactors\ItemMergeInteractor->saveItem(Wikibase\DataModel\Entity\Item, Wikibase\Lib\Summary, User, boolean, array)
#12 /srv/mediawiki/php-1.40.0-wmf.1/extensions/Wikibase/repo/includes/Interactors/ItemMergeInteractor.php(177): Wikibase\Repo\Interactors\ItemMergeInteractor->attemptSaveMerge(Wikibase\DataModel\Entity\Item, Wikibase\DataModel\Entity\Item, string, User, boolean, array)
#13 /srv/mediawiki/php-1.40.0-wmf.1/extensions/Wikibase/repo/includes/Api/MergeItems.php(157): Wikibase\Repo\Interactors\ItemMergeInteractor->mergeItems(Wikibase\DataModel\Entity\ItemId, Wikibase\DataModel\Entity\ItemId, DerivativeContext, array, string, boolean, array)
#14 /srv/mediawiki/php-1.40.0-wmf.1/extensions/Wikibase/repo/includes/Api/MergeItems.php(137): Wikibase\Repo\Api\MergeItems->mergeItems(Wikibase\DataModel\Entity\ItemId, Wikibase\DataModel\Entity\ItemId, array, string, boolean, array)
#15 /srv/mediawiki/php-1.40.0-wmf.1/includes/api/ApiMain.php(1900): Wikibase\Repo\Api\MergeItems->execute()
#16 /srv/mediawiki/php-1.40.0-wmf.1/includes/api/ApiMain.php(875): ApiMain->executeAction()
#17 /srv/mediawiki/php-1.40.0-wmf.1/includes/api/ApiMain.php(846): ApiMain->executeActionWithErrorHandling()
#18 /srv/mediawiki/php-1.40.0-wmf.1/api.php(90): ApiMain->execute()
#19 /srv/mediawiki/php-1.40.0-wmf.1/api.php(45): wfApiMain()
#20 /srv/mediawiki/w/api.php(3): require(string)
#21 {main}Impact
- merging is rather uncommon and requires special rights, so this does not happen too often, not a DDOS vector
- it does add some very minor logspam
- The first occurance seems to have been on 2022-08-08
- All of these errors seem to originate from api.php, though the special page is also not reacting great
Acceptance criteria
- Verify that no changes are done if a merge fails with an EntityTooBigException (IIRC, merging requires multiple edits to different Items - Is it possible to put all of them into some sort of "transaction"?)
- The API responds with a proper Error instead of an unmitigated Exception
- If we have any user interface that use this API: they react meaningful to that error
- (potentially a separate task, to figure out when we start working on this): Special:Merge shows a helpful error message and is not be performing a partial operation
- see T314763#8137822
- We have some tracking in place to record how often an operation is denied due to the Entity being too big
Notes
- This task is about an uncaught exception bubbling up instead of presenting the user with a meaningful error message. For the underlying issue of our entities getting too large, see T320940: Wikidata Entities are getting too big
- other reports about this: T314763: Merging Wikidata items triggers EntityContentTooBigException
- This is effectively a follow-up to T217741: Catch Exceptions where the entity can not be serialized due to being too big and Log & present the user with a nice error in APIs, where the api endpoint to merge entities was seemingly overlooked.