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Fix parallel operations that prevent oldest xmin from advancing.

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While determining xid horizons, we skip over backends that are running
Vacuum. We also ignore Create Index Concurrently, or Reindex Concurrently
for the purposes of computing Xmin for Vacuum. But we were not setting the
flags corresponding to these operations when they are performed in
parallel which was preventing Xid horizon from advancing.

The optimization related to skipping Create Index Concurrently, or Reindex
Concurrently operations was implemented in PG-14 but the fix is the same
for the Parallel Vacuum as well so back-patched till PG-13.

Author: Masahiko Sawada
Reviewed-by: Amit Kapila
Backpatch-through: 13
Discussion: https://postgr.es/m/CAD21AoCLQqgM1sXh9BrDFq0uzd3RBFKi=Vfo6cjjKODm0Onr5w@mail.gmail.com
This commit is contained in:
Amit Kapila
2021-11-19 09:04:40 +05:30
parent 0cd6d3b3c5
commit 0f0cfb4940
4 changed files with 35 additions and 2 deletions
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17
src/backend/storage/ipc/procarray.c
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@@ -2638,6 +2638,10 @@ ProcArrayInstallImportedXmin(TransactionId xmin,
* PGPROC of the transaction from which we imported the snapshot, rather than
* an XID.
*
* Note that this function also copies statusFlags from the source `proc` in
* order to avoid the case where MyProc's xmin needs to be skipped for
* computing xid horizon.
*
* Returns true if successful, false if source xact is no longer running.
*/
bool
@@ -2649,8 +2653,10 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
Assert(TransactionIdIsNormal(xmin));
Assert(proc != NULL);
/* Get lock so source xact can't end while we're doing this */
LWLockAcquire(ProcArrayLock, LW_SHARED);
/*
* Get an exclusive lock so that we can copy statusFlags from source proc.
*/
LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
/*
* Be certain that the referenced PGPROC has an advertised xmin which is
@@ -2663,7 +2669,14 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
TransactionIdIsNormal(xid) &&
TransactionIdPrecedesOrEquals(xid, xmin))
{
/* Install xmin */
MyProc->xmin = TransactionXmin = xmin;
/* Flags being copied must be valid copy-able flags. */
Assert((proc->statusFlags & (~PROC_COPYABLE_FLAGS)) == 0);
MyProc->statusFlags = proc->statusFlags;
ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
result = true;
}