Having to update the just-inserted RecentChanges entry in FlaggedRevsHooks is very expensive and sometimes fails. See for example:
2016-03-21 09:17:09 mw1161 ruwiki 1.27.0-wmf.17 exception ERROR: [9a801118] /rpc/RunJobs.php?wiki=ruwiki&type=ChangeNotification&maxtime=60&maxmem=300M DBQueryError from line 934 of /srv/mediawiki/php-1.27.0-wmf.17/includes/db/Database.php: A database error has occurred. Did you forget to run maintenance/update.php after upgrading? See: https://www.mediawiki.org/wiki/Manual:Upgrading#Run_the_update_script
Query: UPDATE `recentchanges` SET rc_patrolled = '1' WHERE rc_cur_id = '4078029' AND rc_type = '1' AND (rc_timestamp <= '20151109111526')
Function: RevisionReviewForm::updateRecentChanges
Error: 1205 Lock wait timeout exceeded; try restarting transaction (10.64.16.12)
{"exception_id":"9a801118"}
[Exception DBQueryError] (/srv/mediawiki/php-1.27.0-wmf.17/includes/db/Database.php:934) A database error has occurred. Did you forget to run maintenance/update.php after upgrading? See: https://www.mediawiki.org/wiki/Manual:Upgrading#Run_the_update_script
Query: UPDATE `recentchanges` SET rc_patrolled = '1' WHERE rc_cur_id = '4078029' AND rc_type = '1' AND (rc_timestamp <= '20151109111526')
Function: RevisionReviewForm::updateRecentChanges
Error: 1205 Lock wait timeout exceeded; try restarting transaction (10.64.16.12)
#0 /srv/mediawiki/php-1.27.0-wmf.17/includes/db/Database.php(901): DatabaseBase->reportQueryError(string, integer, string, string, boolean)
#1 /srv/mediawiki/php-1.27.0-wmf.17/includes/db/Database.php(1511): DatabaseBase->query(string, string)
#2 /srv/mediawiki/php-1.27.0-wmf.17/extensions/FlaggedRevs/business/RevisionReviewForm.php(569): DatabaseBase->update(string, array, array, string, array)
#3 /srv/mediawiki/php-1.27.0-wmf.17/extensions/FlaggedRevs/backend/FlaggedRevs.hooks.php(649): RevisionReviewForm::updateRecentChanges(RecentChange, string, FlaggedRevision)
#4 /srv/mediawiki/php-1.27.0-wmf.17/includes/Hooks.php(195): FlaggedRevsHooks::autoMarkPatrolled(RecentChange)
#5 /srv/mediawiki/php-1.27.0-wmf.17/includes/changes/RecentChange.php(315): Hooks::run(string, array)
#6 /srv/mediawiki/php-1.27.0-wmf.17/extensions/Wikidata/extensions/Wikibase/client/includes/Changes/WikiPageUpdater.php(152): RecentChange->save()
#7 /srv/mediawiki/php-1.27.0-wmf.17/extensions/Wikidata/extensions/Wikibase/client/includes/Changes/ChangeHandler.php(256): Wikibase\Client\Changes\WikiPageUpdater->injectRCRecords(array, Wikibase\ItemChange)
#8 /srv/mediawiki/php-1.27.0-wmf.17/extensions/Wikidata/extensions/Wikibase/client/includes/Changes/ChangeHandler.php(175): Wikibase\Client\Changes\ChangeHandler->applyUpdateAction(string, array, Wikibase\ItemChange)
#9 /srv/mediawiki/php-1.27.0-wmf.17/extensions/Wikidata/extensions/Wikibase/client/includes/Changes/ChangeHandler.php(141): Wikibase\Client\Changes\ChangeHandler->handleChange(Wikibase\ItemChange)
#10 /srv/mediawiki/php-1.27.0-wmf.17/extensions/Wikidata/extensions/Wikibase/lib/includes/ChangeNotificationJob.php(124): Wikibase\Client\Changes\ChangeHandler->handleChanges(array)
#11 /srv/mediawiki/php-1.27.0-wmf.17/includes/jobqueue/JobRunner.php(263): Wikibase\ChangeNotificationJob->run()
#12 /srv/mediawiki/php-1.27.0-wmf.17/includes/jobqueue/JobRunner.php(177): JobRunner->executeJob(Wikibase\ChangeNotificationJob, BufferingStatsdDataFactory, integer)
#13 /srv/mediawiki/rpc/RunJobs.php(47): JobRunner->run(array)
#14 {main}FlaggedRevs should be able to use a hook that runs in RecentChanges::save (pre-save) in order to change the value of rc_patrolled pre-save so that we already have the right value in the initial insert.