>From 3f800e9363909d2fcf80cb5f9b4f68579a3cb328 Mon Sep 17 00:00:00 2001 From: Andres Freund Date: Sun, 1 Feb 2015 21:04:42 +0100 Subject: [PATCH] Heavily-WIP: Cache snapshots in GetSnapshotData() --- src/backend/commands/cluster.c | 1 + src/backend/storage/ipc/procarray.c | 67 ++++++++++++++++++++++++++++++++----- src/backend/storage/lmgr/proc.c | 13 +++++++ src/include/storage/proc.h | 6 ++++ 4 files changed, 78 insertions(+), 9 deletions(-) diff --git a/src/backend/commands/cluster.c b/src/backend/commands/cluster.c index dc1b37c..3def86a 100644 --- a/src/backend/commands/cluster.c +++ b/src/backend/commands/cluster.c @@ -1558,6 +1558,7 @@ finish_heap_swap(Oid OIDOldHeap, Oid OIDNewHeap, elog(ERROR, "cache lookup failed for relation %u", OIDOldHeap); relform = (Form_pg_class) GETSTRUCT(reltup); + Assert(TransactionIdIsNormal(frozenXid)); relform->relfrozenxid = frozenXid; relform->relminmxid = cutoffMulti; diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c index a1ebc72..66be489 100644 --- a/src/backend/storage/ipc/procarray.c +++ b/src/backend/storage/ipc/procarray.c @@ -421,6 +421,8 @@ ProcArrayEndTransaction(PGPROC *proc, TransactionId latestXid) latestXid)) ShmemVariableCache->latestCompletedXid = latestXid; + ProcGlobal->cached_snapshot_valid = false; + LWLockRelease(ProcArrayLock); } else @@ -1403,6 +1405,8 @@ GetSnapshotData(Snapshot snapshot) errmsg("out of memory"))); } + snapshot->takenDuringRecovery = RecoveryInProgress(); + /* * It is sufficient to get shared lock on ProcArrayLock, even if we are * going to set MyPgXact->xmin. @@ -1417,9 +1421,32 @@ GetSnapshotData(Snapshot snapshot) /* initialize xmin calculation with xmax */ globalxmin = xmin = xmax; - snapshot->takenDuringRecovery = RecoveryInProgress(); + if (!snapshot->takenDuringRecovery && ProcGlobal->cached_snapshot_valid) + { + Snapshot csnap = &ProcGlobal->cached_snapshot; + TransactionId *saved_xip; + TransactionId *saved_subxip; + + saved_xip = snapshot->xip; + saved_subxip = snapshot->subxip; + + memcpy(snapshot, csnap, sizeof(SnapshotData)); + + snapshot->xip = saved_xip; + snapshot->subxip = saved_subxip; + + memcpy(snapshot->xip, csnap->xip, + sizeof(TransactionId) * csnap->xcnt); + memcpy(snapshot->subxip, csnap->subxip, + sizeof(TransactionId) * csnap->subxcnt); - if (!snapshot->takenDuringRecovery) + globalxmin = ProcGlobal->cached_snapshot_globalxmin; + xmin = csnap->xmin; + + Assert(TransactionIdIsValid(globalxmin)); + Assert(TransactionIdIsValid(xmin)); + } + else if (!snapshot->takenDuringRecovery) { int *pgprocnos = arrayP->pgprocnos; int numProcs; @@ -1437,14 +1464,11 @@ GetSnapshotData(Snapshot snapshot) TransactionId xid; /* - * Backend is doing logical decoding which manages xmin - * separately, check below. + * Ignore procs running LAZY VACUUM (which don't need to retain + * rows) and backends doing logical decoding (which manages xmin + * separately, check below). */ - if (pgxact->vacuumFlags & PROC_IN_LOGICAL_DECODING) - continue; - - /* Ignore procs running LAZY VACUUM */ - if (pgxact->vacuumFlags & PROC_IN_VACUUM) + if (pgxact->vacuumFlags & (PROC_IN_LOGICAL_DECODING | PROC_IN_VACUUM)) continue; /* Update globalxmin to be the smallest valid xmin */ @@ -1513,6 +1537,31 @@ GetSnapshotData(Snapshot snapshot) } } } + + /* upate cache */ + { + Snapshot csnap = &ProcGlobal->cached_snapshot; + TransactionId *saved_xip; + TransactionId *saved_subxip; + + ProcGlobal->cached_snapshot_globalxmin = globalxmin; + + saved_xip = csnap->xip; + saved_subxip = csnap->subxip; + memcpy(csnap, snapshot, sizeof(SnapshotData)); + csnap->xip = saved_xip; + csnap->subxip = saved_subxip; + + /* not yet stored. Yuck */ + csnap->xmin = xmin; + + memcpy(csnap->xip, snapshot->xip, + sizeof(TransactionId) * csnap->xcnt); + memcpy(csnap->subxip, snapshot->subxip, + sizeof(TransactionId) * csnap->subxcnt); + ProcGlobal->cached_snapshot_valid = true; + } + } else { diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 65e8afe..a6ef687 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -112,6 +112,13 @@ ProcGlobalShmemSize(void) size = add_size(size, mul_size(NUM_AUXILIARY_PROCS, sizeof(PGXACT))); size = add_size(size, mul_size(max_prepared_xacts, sizeof(PGXACT))); + /* for the cached snapshot */ +#define PROCARRAY_MAXPROCS (MaxBackends + max_prepared_xacts) + size = add_size(size, mul_size(sizeof(TransactionId), PROCARRAY_MAXPROCS)); +#define TOTAL_MAX_CACHED_SUBXIDS \ + ((PGPROC_MAX_CACHED_SUBXIDS + 1) * PROCARRAY_MAXPROCS) + size = add_size(size, mul_size(sizeof(TransactionId), TOTAL_MAX_CACHED_SUBXIDS)); + return size; } @@ -269,6 +276,12 @@ InitProcGlobal(void) /* Create ProcStructLock spinlock, too */ ProcStructLock = (slock_t *) ShmemAlloc(sizeof(slock_t)); SpinLockInit(ProcStructLock); + + /* cached snapshot */ + ProcGlobal->cached_snapshot_valid = false; + ProcGlobal->cached_snapshot.xip = ShmemAlloc(PROCARRAY_MAXPROCS * sizeof(TransactionId)); + ProcGlobal->cached_snapshot.subxip = ShmemAlloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId)); + ProcGlobal->cached_snapshot_globalxmin = InvalidTransactionId; } /* diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index d194f38..f483d3b 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -16,6 +16,7 @@ #include "access/xlogdefs.h" #include "lib/ilist.h" +#include "utils/snapshot.h" #include "storage/latch.h" #include "storage/lock.h" #include "storage/pg_sema.h" @@ -206,6 +207,11 @@ typedef struct PROC_HDR int startupProcPid; /* Buffer id of the buffer that Startup process waits for pin on, or -1 */ int startupBufferPinWaitBufId; + + /* Cached snapshot */ + bool cached_snapshot_valid; + SnapshotData cached_snapshot; + TransactionId cached_snapshot_globalxmin; } PROC_HDR; extern PROC_HDR *ProcGlobal; -- 2.2.1.212.gc5b9256