dcausse moved this task from In Progress to Needs Reporting on the Discovery-Search (Current work) board. dcausse closed this task as "Declined". dcausse added a comment.
I did not find anything obvious but looking at the various classes involved in managing the writes I see excessive locking protection and object reuse esp: - WriteCacheService <https://github.com/wikimedia/wikidata-query-blazegraph/blob/master/bigdata-core/bigdata/src/java/com/bigdata/io/writecache/WriteCacheService.java#L275> which keeps and reuses WriteCache instances. - WriteCache <https://github.com/wikimedia/wikidata-query-blazegraph/blob/master/bigdata-core/bigdata/src/java/com/bigdata/io/writecache/WriteCache.java#L192> which (protects?) wrap access to a ByteBuffer - DirectBufferPool <https://github.com/wikimedia/wikidata-query-blazegraph/blob/master/bigdata-core/bigdata/src/java/com/bigdata/io/DirectBufferPool.java#L278> which according to comments seems to have issues managing its references: //When DEBUG is true we do not permit a buffer which was not correctly release to be reused// which in other words means //When DEBUG is **false** we **do** permit a buffer which was not correctly release to be **reused**// Given the high number different locks being used a race condition might allow the buffer to be written from different threads leading to the checkum being computed before a subsequent write to this same buffer. Recovering the journal does not seem possible. Declining as I'm not sure it is worth spending more efforts on this, finding the real issue in this code base seems unlikely. TASK DETAIL https://phabricator.wikimedia.org/T263110 WORKBOARD https://phabricator.wikimedia.org/project/board/1227/ EMAIL PREFERENCES https://phabricator.wikimedia.org/settings/panel/emailpreferences/ To: dcausse Cc: CBogen, dcausse, Aklapper, Akuckartz, darthmon_wmde, Nandana, Namenlos314, Lahi, Gq86, Lucas_Werkmeister_WMDE, GoranSMilovanovic, QZanden, EBjune, merbst, LawExplorer, _jensen, rosalieper, Scott_WUaS, Jonas, Xmlizer, jkroll, Wikidata-bugs, Jdouglas, aude, Tobias1984, Manybubbles, Mbch331
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