Summary:
The patch fixes an improbable race condition between AddPrepared from one write queue and AdvanceMaxEvictedSeq from another queue. In this scenario AddPrepared finds prepare_seq lower than max and adding to PrepareHeap as usual while AdvanceMaxEvictedSeq has finished checking PrepareHeap against the future max. Thus when AdvanceMaxEvictedSeq finishes off by updating the max_evicted_seq_, PrepareHeap ends up with a prepared_seq lower than it which breaks the PrepareHeap contract. The fix is that in AddPrepared we check against the future_max_evicted_seq_ instead, which is update before AdvanceMaxEvictedSeq acquire prepare_mutex_ and looks into PrepareHeap.
A unit test added to test for the failure scenario. The code is also refactored a bit to remove the duplicate code between AdvanceMaxEvictedSeq and AddPrepared.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5025
Differential Revision: D14249028
Pulled By: maysamyabandeh
fbshipit-source-id: 072ea56663f40359662c05fafa6ac524417b0622
04a2631dbe