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Commit4b373e4

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Improve C comments in GetSnapshotData.
Move discussion of why our algorithm for taking snapshots in recoveryto a more appropriate location in the function, and delete incorrectmention of taking a lock.
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‎src/backend/storage/ipc/procarray.c

Lines changed: 6 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -1307,14 +1307,6 @@ GetSnapshotData(Snapshot snapshot)
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/* initialize xmin calculation with xmax */
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globalxmin=xmin=xmax;
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/*
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* If we're in recovery then snapshot data comes from a different place,
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* so decide which route we take before grab the lock. It is possible for
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* recovery to end before we finish taking snapshot, and for newly
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* assigned transaction ids to be added to the procarray. Xmax cannot
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* change while we hold ProcArrayLock, so those newly added transaction
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* ids would be filtered away, so we need not be concerned about them.
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*/
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snapshot->takenDuringRecovery=RecoveryInProgress();
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if (!snapshot->takenDuringRecovery)
@@ -1429,6 +1421,12 @@ GetSnapshotData(Snapshot snapshot)
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* Either way we need to change the way XidInMVCCSnapshot() works
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* depending upon when the snapshot was taken, or change normal
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* snapshot processing so it matches.
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*
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* Note: It is possible for recovery to end before we finish taking the
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* snapshot, and for newly assigned transaction ids to be added to the
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* ProcArray. xmax cannot change while we hold ProcArrayLock, so those
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* newly added transaction ids would be filtered away, so we need not
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* be concerned about them.
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*/
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subcount=KnownAssignedXidsGetAndSetXmin(snapshot->subxip,&xmin,
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xmax);

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