It doesn't happen every time, but often. It's intermittent. Even within a single job some writes succeed, and then another one fails.
Tue Feb 10 5:58:38 UTC 2015 integration-slave1006 build276 SqlBagOStuff::set/single-row 5 database is locked REPLACE INTO objectcache (keyname,value,exptime) VALUES ('build276:resourceloader:modulemodifiedhash:mediawiki.language.data:ade3504093df2f931359f1c5028d085d',x'15cacb09c0200c00d05d3241cc879a388d54450f4221bd95ee5efaceaf3af9132e0eb3c68412cee4505b674541e336681827561be954a4dc306bfb9f39dc6bf7b8ebbea02c4f42ac7258cae5fd00','20380119031407')
DatabaseBase::query: Writes done: REPLACE INTO objectcache (keyname,value,exptime) VALUES ('X') SQL ERROR: database is locked [SQLBagOStuff] DBError: 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: REPLACE INTO objectcache (keyname,value,exptime) VALUES ('build276:resourceloader:modulemodifiedhash:mediawiki.language.data:ade3504093df2f931359f1c5028d085d',x'15cacb09c0200c00d05d3241cc879a388d54450f4221bd95ee5efaceaf3af9132e0eb3c68412cee4505b674541e336681827561be954a4dc306bfb9f39dc6bf7b8ebbea02c4f42ac7258cae5fd00','20380119031407') Function: SqlBagOStuff::set/single-row Error: 5 database is locked [SQLBagOStuff] SqlBagOStuff::handleWriteError: ignoring query error LoadBalancer::getConnection: using server for group LoadBalancer::getConnection: using server for group DatabaseBase::query: Writes done: PRAGMA case_sensitive_like = N Connected to database 0 at DatabaseBase::query: Writes done: REPLACE INTO objectcache (keyname,value,exptime) VALUES ('X') SQL ERROR (ignored): database is locked DatabaseBase::query: Writes done: DELETE FROM l10n_cache WHERE lc_lang = 'X' LoadBalancer::getConnection: using server for group LoadBalancer::getConnection: using server for group LoadBalancer::getConnection: using server for group LocalisationCache::isExpired(ar): cache missing, need to make one DatabaseBase::query: Writes done: INSERT INTO l10n_cache (lc_lang,lc_key,lc_value) VALUES ('X') DatabaseBase::query: Writes done: INSERT INTO l10n_cache (lc_lang,lc_key,lc_value) VALUES ('X') LocalisationCache::recache: got localisation for ar from source DatabaseBase::query: Writes done: INSERT INTO l10n_cache (lc_lang,lc_key,lc_value) VALUES ('X') DatabaseBase::query: Writes done: INSERT INTO l10n_cache (lc_lang,lc_key,lc_value) VALUES ('X')