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Commit0f0cfb4

Browse files
author
Amit Kapila
committed
Fix parallel operations that prevent oldest xmin from advancing.
While determining xid horizons, we skip over backends that are runningVacuum. We also ignore Create Index Concurrently, or Reindex Concurrentlyfor the purposes of computing Xmin for Vacuum. But we were not setting theflags corresponding to these operations when they are performed inparallel which was preventing Xid horizon from advancing.The optimization related to skipping Create Index Concurrently, or ReindexConcurrently operations was implemented in PG-14 but the fix is the samefor the Parallel Vacuum as well so back-patched till PG-13.Author: Masahiko SawadaReviewed-by: Amit KapilaBackpatch-through: 13Discussion:https://postgr.es/m/CAD21AoCLQqgM1sXh9BrDFq0uzd3RBFKi=Vfo6cjjKODm0Onr5w@mail.gmail.com
1 parent0cd6d3b commit0f0cfb4

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4 files changed

+35
-2
lines changed

4 files changed

+35
-2
lines changed

‎src/backend/access/heap/vacuumlazy.c

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -4159,6 +4159,12 @@ parallel_vacuum_main(dsm_segment *seg, shm_toc *toc)
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LVRelStatevacrel;
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ErrorContextCallbackerrcallback;
41614161

4162+
/*
4163+
* A parallel vacuum worker must have only PROC_IN_VACUUM flag since we
4164+
* don't support parallel vacuum for autovacuum as of now.
4165+
*/
4166+
Assert(MyProc->statusFlags==PROC_IN_VACUUM);
4167+
41624168
lvshared= (LVShared*)shm_toc_lookup(toc,PARALLEL_VACUUM_KEY_SHARED,
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false);
41644170
elevel=lvshared->elevel;

‎src/backend/access/nbtree/nbtsort.c

Lines changed: 7 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1808,6 +1808,13 @@ _bt_parallel_build_main(dsm_segment *seg, shm_toc *toc)
18081808
ResetUsage();
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#endif/* BTREE_BUILD_STATS */
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1811+
/*
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* The only possible status flag that can be set to the parallel worker is
1813+
* PROC_IN_SAFE_IC.
1814+
*/
1815+
Assert((MyProc->statusFlags==0)||
1816+
(MyProc->statusFlags==PROC_IN_SAFE_IC));
1817+
18111818
/* Set debug_query_string for individual workers first */
18121819
sharedquery=shm_toc_lookup(toc,PARALLEL_KEY_QUERY_TEXT, true);
18131820
debug_query_string=sharedquery;

‎src/backend/storage/ipc/procarray.c

Lines changed: 15 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -2638,6 +2638,10 @@ ProcArrayInstallImportedXmin(TransactionId xmin,
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* PGPROC of the transaction from which we imported the snapshot, rather than
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* an XID.
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*
2641+
* Note that this function also copies statusFlags from the source `proc` in
2642+
* order to avoid the case where MyProc's xmin needs to be skipped for
2643+
* computing xid horizon.
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*
26412645
* Returns true if successful, false if source xact is no longer running.
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*/
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bool
@@ -2649,8 +2653,10 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
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Assert(TransactionIdIsNormal(xmin));
26502654
Assert(proc!=NULL);
26512655

2652-
/* Get lock so source xact can't end while we're doing this */
2653-
LWLockAcquire(ProcArrayLock,LW_SHARED);
2656+
/*
2657+
* Get an exclusive lock so that we can copy statusFlags from source proc.
2658+
*/
2659+
LWLockAcquire(ProcArrayLock,LW_EXCLUSIVE);
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26552661
/*
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* Be certain that the referenced PGPROC has an advertised xmin which is
@@ -2663,7 +2669,14 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
26632669
TransactionIdIsNormal(xid)&&
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TransactionIdPrecedesOrEquals(xid,xmin))
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{
2672+
/* Install xmin */
26662673
MyProc->xmin=TransactionXmin=xmin;
2674+
2675+
/* Flags being copied must be valid copy-able flags. */
2676+
Assert((proc->statusFlags& (~PROC_COPYABLE_FLAGS))==0);
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MyProc->statusFlags=proc->statusFlags;
2678+
ProcGlobal->statusFlags[MyProc->pgxactoff]=MyProc->statusFlags;
2679+
26672680
result= true;
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}
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‎src/include/storage/proc.h

Lines changed: 7 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -65,6 +65,13 @@ struct XidCache
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#definePROC_VACUUM_STATE_MASK \
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(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND)
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68+
/*
69+
* Flags that are valid to copy from another proc, the parallel leader
70+
* process in practice. Currently, flags that are set during parallel
71+
* vacuum and parallel index creation are allowed.
72+
*/
73+
#definePROC_COPYABLE_FLAGS (PROC_IN_VACUUM | PROC_IN_SAFE_IC)
74+
6875
/*
6976
* We allow a small number of "weak" relation locks (AccessShareLock,
7077
* RowShareLock, RowExclusiveLock) to be recorded in the PGPROC structure

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