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  1. Core Server
  2. SERVER-48327

[4.4] Index build abort can set ghost timestamps on primaries

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    • Bug
    • Status: Closed
    • Major - P3
    • Resolution: Won't Fix
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      Apply this patch:

      diff --git a/src/mongo/db/catalog/multi_index_block.cpp b/src/mongo/db/catalog/multi_index_block.cpp
      index f08446efb6..d2a94dac78 100644
      --- a/src/mongo/db/catalog/multi_index_block.cpp
      +++ b/src/mongo/db/catalog/multi_index_block.cpp
      @@ -115,6 +115,8 @@ void MultiIndexBlock::abortIndexBuild(OperationContext* opCtx,
                       repl::UnreplicatedWritesBlock uwb(opCtx);
                       if (!IndexTimestampHelper::setGhostCommitTimestampForCatalogWrite(opCtx, nss)) {
                           LOGV2(20382, "Did not timestamp index abort write.");
      +                } else {
      +                    LOGV2_FATAL(0, "Wrote ghost timestamp for index abort write.");
                       }
                   }
      

      And run:

      resmoke run --suite=no_passthrough jstests/noPassthrough/index_stepdown_abort_prepare_conflict.js
      

      Show
      Apply this patch: diff --git a/src/mongo/db/catalog/multi_index_block.cpp b/src/mongo/db/catalog/multi_index_block.cpp index f08446efb6..d2a94dac78 100644 --- a/src/mongo/db/catalog/multi_index_block.cpp +++ b/src/mongo/db/catalog/multi_index_block.cpp @@ - 115 , 6 + 115 , 8 @@ void MultiIndexBlock::abortIndexBuild(OperationContext* opCtx, repl::UnreplicatedWritesBlock uwb(opCtx); if (!IndexTimestampHelper::setGhostCommitTimestampForCatalogWrite(opCtx, nss)) { LOGV2( 20382 , "Did not timestamp index abort write." ); + } else { + LOGV2_FATAL( 0 , "Wrote ghost timestamp for index abort write." ); } } And run: resmoke run --suite=no_passthrough jstests/noPassthrough/index_stepdown_abort_prepare_conflict.js
    • Execution Team 2020-06-01, Execution Team 2020-06-15, Execution Team 2021-02-08
    • 22

    Description

      When aborting an index build, we determine whether or not to write a ghost timestamp through a call to "getCommitTimestamp" here, however this only returns a timestamp on secondaries.

      On primaries, this is always false, and results in a call to RecoveryUnit::setTimestamp.

      This is immediately followed by a call to write an abortIndexBuild oplog entry via the onCleanUp handler. This overwrites and updates the commit timestamp, so the catalog write ends up being timestamped correctly.

      TLDR: I believe this can temporarily cause the WiredTiger "all_durable" value to move backwards, which violates the contract "all_durable" on primaries.

      Say, for example, there are no open WT transactions. Both lastApplied and "all_durable" all 10. If I open a WT transaction and set its commit timestamp to 10 (a timestamp that has already been committed), "all_durable" will move backwards to 9. After the transaction commits, "all_durable" can advance back to 10.

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              louis.williams@mongodb.com Louis Williams
              louis.williams@mongodb.com Louis Williams
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                Created:
                Updated:
                Resolved: