From 33b6dd83e26f06c96e7d54af534a70476749cbab Mon Sep 17 00:00:00 2001 From: Amit Kapila Date: Fri, 19 Nov 2021 09:24:00 +0530 Subject: [PATCH] Fix parallel operations that prevent oldest xmin from advancing. 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 --- src/backend/access/heap/vacuumlazy.c | 6 ++++++ src/backend/storage/ipc/procarray.c | 16 ++++++++++++++-- src/include/storage/proc.h | 7 +++++++ 3 files changed, 27 insertions(+), 2 deletions(-) diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c index fe2a6062b9c..e1bb97951b0 100644 --- a/src/backend/access/heap/vacuumlazy.c +++ b/src/backend/access/heap/vacuumlazy.c @@ -3482,6 +3482,12 @@ parallel_vacuum_main(dsm_segment *seg, shm_toc *toc) LVRelStats vacrelstats; ErrorContextCallback errcallback; + /* + * A parallel vacuum worker must have only PROC_IN_VACUUM flag since we + * don't support parallel vacuum for autovacuum as of now. + */ + Assert(MyPgXact->vacuumFlags == PROC_IN_VACUUM); + lvshared = (LVShared *) shm_toc_lookup(toc, PARALLEL_VACUUM_KEY_SHARED, false); elevel = lvshared->elevel; diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c index 828ed2a38a1..2f1d4af17a5 100644 --- a/src/backend/storage/ipc/procarray.c +++ b/src/backend/storage/ipc/procarray.c @@ -1864,6 +1864,10 @@ ProcArrayInstallImportedXmin(TransactionId xmin, * PGPROC of the transaction from which we imported the snapshot, rather than * an XID. * + * Note that this function also copies vacuumFlags from the source `proc` in + * order to avoid the case where MyPgXact's xmin needs to be skipped for + * computing xid horizon. + * * Returns true if successful, false if source xact is no longer running. */ bool @@ -1876,8 +1880,10 @@ 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 vacuumFlags from source proc. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); pgxact = &allPgXact[proc->pgprocno]; @@ -1892,7 +1898,13 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc) TransactionIdIsNormal(xid) && TransactionIdPrecedesOrEquals(xid, xmin)) { + /* Install xmin */ MyPgXact->xmin = TransactionXmin = xmin; + + /* Flags being copied must be valid copy-able flags. */ + Assert((pgxact->vacuumFlags & (~PROC_COPYABLE_FLAGS)) == 0); + MyPgXact->vacuumFlags = pgxact->vacuumFlags; + result = true; } diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 1ee9000b2b9..b3ea1a25860 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -62,6 +62,13 @@ struct XidCache #define PROC_VACUUM_STATE_MASK \ (PROC_IN_VACUUM | PROC_IN_ANALYZE | PROC_VACUUM_FOR_WRAPAROUND) +/* + * Flags that are valid to copy from another proc, the parallel leader + * process in practice. Currently, a flag that is set during parallel + * vacuum is allowed. + */ +#define PROC_COPYABLE_FLAGS (PROC_IN_VACUUM) + /* * We allow a small number of "weak" relation locks (AccessShareLock, * RowShareLock, RowExclusiveLock) to be recorded in the PGPROC structure