snapshot scalability: Move delayChkpt from PGXACT to PGPROC.

The goal of separating hotly accessed per-backend data from PGPROC
into PGXACT is to make accesses fast (GetSnapshotData() in
particular). But delayChkpt is not actually accessed frequently; only
when starting a checkpoint. As it is frequently modified (multiple
times in the course of a single transaction), storing it in the same
cacheline as hotly accessed data unnecessarily dirties a contended
cacheline.

Therefore move delayChkpt to PGPROC.

This is part of a larger series of patches intending to improve
GetSnapshotData() scalability. It is committed and pushed separately,
as it is independently beneficial (small but measurable win, limited
by the other frequent modifications of PGXACT).

Author: Andres Freund
Reviewed-By: Robert Haas, Thomas Munro, David Rowley
Discussion: https://postgr.es/m/20200301083601.ews6hz5dduc3w2se@alap3.anarazel.de

diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c
index fdd0394ffae53fbfbcbec40266a05087984b8109..70d0e1c215f3b21e9d08f29f9af34634b181c696 100644 (file)
--- a/src/backend/access/transam/multixact.c
+++ b/src/backend/access/transam/multixact.c
@@ -3058,8 +3058,8 @@ TruncateMultiXact(MultiXactId newOldestMulti, Oid newOldestMultiDB)
     * crash/basebackup, even though the state of the data directory would
     * require it.
     */
-   Assert(!MyPgXact->delayChkpt);
-   MyPgXact->delayChkpt = true;
+   Assert(!MyProc->delayChkpt);
+   MyProc->delayChkpt = true;
 
    /* WAL log truncation */
    WriteMTruncateXlogRec(newOldestMultiDB,
@@ -3085,7 +3085,7 @@ TruncateMultiXact(MultiXactId newOldestMulti, Oid newOldestMultiDB)
    /* Then offsets */
    PerformOffsetsTruncation(oldestMulti, newOldestMulti);
 
-   MyPgXact->delayChkpt = false;
+   MyProc->delayChkpt = false;
 
    END_CRIT_SECTION();
    LWLockRelease(MultiXactTruncationLock);

diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 5adf956f4133e98d836ac295d5e51748f644df05..2f7d4ed59a87ce4756d9543a2f3288009f320256 100644 (file)
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -465,7 +465,7 @@ MarkAsPreparingGuts(GlobalTransaction gxact, TransactionId xid, const char *gid,
    proc->lxid = (LocalTransactionId) xid;
    pgxact->xid = xid;
    pgxact->xmin = InvalidTransactionId;
-   pgxact->delayChkpt = false;
+   proc->delayChkpt = false;
    pgxact->vacuumFlags = 0;
    proc->pid = 0;
    proc->backendId = InvalidBackendId;
@@ -1114,7 +1114,7 @@ EndPrepare(GlobalTransaction gxact)
 
    START_CRIT_SECTION();
 
-   MyPgXact->delayChkpt = true;
+   MyProc->delayChkpt = true;
 
    XLogBeginInsert();
    for (record = records.head; record != NULL; record = record->next)
@@ -1157,7 +1157,7 @@ EndPrepare(GlobalTransaction gxact)
     * checkpoint starting after this will certainly see the gxact as a
     * candidate for fsyncing.
     */
-   MyPgXact->delayChkpt = false;
+   MyProc->delayChkpt = false;
 
    /*
     * Remember that we have this GlobalTransaction entry locked for us.  If
@@ -2204,7 +2204,7 @@ RecordTransactionCommitPrepared(TransactionId xid,
    START_CRIT_SECTION();
 
    /* See notes in RecordTransactionCommit */
-   MyPgXact->delayChkpt = true;
+   MyProc->delayChkpt = true;
 
    /*
     * Emit the XLOG commit record. Note that we mark 2PC commits as
@@ -2252,7 +2252,7 @@ RecordTransactionCommitPrepared(TransactionId xid,
    TransactionIdCommitTree(xid, nchildren, children);
 
    /* Checkpoint can proceed now */
-   MyPgXact->delayChkpt = false;
+   MyProc->delayChkpt = false;
 
    END_CRIT_SECTION();
 

diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index 110ec228eba7521f0225e1d30a52646856f70b28..6b1ae1f981d123e85360e3a27df47a2b3a3e2425 100644 (file)
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -1307,7 +1307,7 @@ RecordTransactionCommit(void)
         * a bit fuzzy, but it doesn't matter.
         */
        START_CRIT_SECTION();
-       MyPgXact->delayChkpt = true;
+       MyProc->delayChkpt = true;
 
        SetCurrentTransactionStopTimestamp();
 
@@ -1408,7 +1408,7 @@ RecordTransactionCommit(void)
     */
    if (markXidCommitted)
    {
-       MyPgXact->delayChkpt = false;
+       MyProc->delayChkpt = false;
        END_CRIT_SECTION();
    }
 

diff --git a/src/backend/access/transam/xloginsert.c b/src/backend/access/transam/xloginsert.c
index 5e032e7042d6f20200b435ddb6fb5cc085c14d46..4259309dbae5961525eda348bf199a1af865b79a 100644 (file)
--- a/src/backend/access/transam/xloginsert.c
+++ b/src/backend/access/transam/xloginsert.c
@@ -904,7 +904,7 @@ XLogSaveBufferForHint(Buffer buffer, bool buffer_std)
    /*
     * Ensure no checkpoint can change our view of RedoRecPtr.
     */
-   Assert(MyPgXact->delayChkpt);
+   Assert(MyProc->delayChkpt);
 
    /*
     * Update RedoRecPtr so that we can make the right decision

diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 7317ac8a2c47cc2e6d185a9bc4e64f22ddf48d91..a7a39dd2a1ef77f00ae5db94a2f40c41e1be7ed4 100644 (file)
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -3587,7 +3587,7 @@ MarkBufferDirtyHint(Buffer buffer, bool buffer_std)
             * essential that CreateCheckpoint waits for virtual transactions
             * rather than full transactionids.
             */
-           MyPgXact->delayChkpt = delayChkpt = true;
+           MyProc->delayChkpt = delayChkpt = true;
            lsn = XLogSaveBufferForHint(buffer, buffer_std);
        }
 
@@ -3620,7 +3620,7 @@ MarkBufferDirtyHint(Buffer buffer, bool buffer_std)
        UnlockBufHdr(bufHdr, buf_state);
 
        if (delayChkpt)
-           MyPgXact->delayChkpt = false;
+           MyProc->delayChkpt = false;
 
        if (dirtied)
        {

diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 281fe671bdf612a8d45cde959a774317b949a37b..363000670b2f919f334dee2e7be4b56aedfaab9a 100644 (file)
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -436,7 +436,7 @@ ProcArrayEndTransaction(PGPROC *proc, TransactionId latestXid)
        pgxact->xmin = InvalidTransactionId;
        /* must be cleared with xid/xmin: */
        pgxact->vacuumFlags &= ~PROC_VACUUM_STATE_MASK;
-       pgxact->delayChkpt = false; /* be sure this is cleared in abort */
+       proc->delayChkpt = false; /* be sure this is cleared in abort */
        proc->recoveryConflictPending = false;
 
        Assert(pgxact->nxids == 0);
@@ -458,7 +458,7 @@ ProcArrayEndTransactionInternal(PGPROC *proc, PGXACT *pgxact,
    pgxact->xmin = InvalidTransactionId;
    /* must be cleared with xid/xmin: */
    pgxact->vacuumFlags &= ~PROC_VACUUM_STATE_MASK;
-   pgxact->delayChkpt = false; /* be sure this is cleared in abort */
+   proc->delayChkpt = false; /* be sure this is cleared in abort */
    proc->recoveryConflictPending = false;
 
    /* Clear the subtransaction-XID cache too while holding the lock */
@@ -616,7 +616,7 @@ ProcArrayClearTransaction(PGPROC *proc)
 
    /* redundant, but just in case */
    pgxact->vacuumFlags &= ~PROC_VACUUM_STATE_MASK;
-   pgxact->delayChkpt = false;
+   proc->delayChkpt = false;
 
    /* Clear the subtransaction-XID cache too */
    pgxact->nxids = 0;
@@ -2257,7 +2257,7 @@ GetOldestSafeDecodingTransactionId(bool catalogOnly)
  * delaying checkpoint because they have critical actions in progress.
  *
  * Constructs an array of VXIDs of transactions that are currently in commit
- * critical sections, as shown by having delayChkpt set in their PGXACT.
+ * critical sections, as shown by having delayChkpt set in their PGPROC.
  *
  * Returns a palloc'd array that should be freed by the caller.
  * *nvxids is the number of valid entries.
@@ -2288,9 +2288,8 @@ GetVirtualXIDsDelayingChkpt(int *nvxids)
    {
        int         pgprocno = arrayP->pgprocnos[index];
        PGPROC     *proc = &allProcs[pgprocno];
-       PGXACT     *pgxact = &allPgXact[pgprocno];
 
-       if (pgxact->delayChkpt)
+       if (proc->delayChkpt)
        {
            VirtualTransactionId vxid;
 
@@ -2328,12 +2327,11 @@ HaveVirtualXIDsDelayingChkpt(VirtualTransactionId *vxids, int nvxids)
    {
        int         pgprocno = arrayP->pgprocnos[index];
        PGPROC     *proc = &allProcs[pgprocno];
-       PGXACT     *pgxact = &allPgXact[pgprocno];
        VirtualTransactionId vxid;
 
        GET_VXID_FROM_PGPROC(vxid, *proc);
 
-       if (pgxact->delayChkpt && VirtualTransactionIdIsValid(vxid))
+       if (proc->delayChkpt && VirtualTransactionIdIsValid(vxid))
        {
            int         i;
 

diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c
index baecb39787f341e12ea71038f2d2f25d985574c6..04a5d595e4d982542e7350d9842c25fa4a95b8d5 100644 (file)
--- a/src/backend/storage/lmgr/proc.c
+++ b/src/backend/storage/lmgr/proc.c
@@ -397,7 +397,7 @@ InitProcess(void)
    MyProc->roleId = InvalidOid;
    MyProc->tempNamespaceId = InvalidOid;
    MyProc->isBackgroundWorker = IsBackgroundWorker;
-   MyPgXact->delayChkpt = false;
+   MyProc->delayChkpt = false;
    MyPgXact->vacuumFlags = 0;
    /* NB -- autovac launcher intentionally does not set IS_AUTOVACUUM */
    if (IsAutoVacuumWorkerProcess())
@@ -579,7 +579,7 @@ InitAuxiliaryProcess(void)
    MyProc->roleId = InvalidOid;
    MyProc->tempNamespaceId = InvalidOid;
    MyProc->isBackgroundWorker = IsBackgroundWorker;
-   MyPgXact->delayChkpt = false;
+   MyProc->delayChkpt = false;
    MyPgXact->vacuumFlags = 0;
    MyProc->lwWaiting = false;
    MyProc->lwWaitMode = 0;

diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h
index d21780108bbd60713baa1fda3dbc4015169f5b3d..ae4f573ab46fa4e52adb325bca0f9791c182978d 100644 (file)
--- a/src/include/storage/proc.h
+++ b/src/include/storage/proc.h
@@ -142,6 +142,8 @@ struct PGPROC
    LOCKMASK    heldLocks;      /* bitmask for lock types already held on this
                                 * lock object by this backend */
 
+   bool        delayChkpt;     /* true if this proc delays checkpoint start */
+
    /*
     * Info to allow us to wait for synchronous replication, if needed.
     * waitLSN is InvalidXLogRecPtr if not waiting; set only by user backend.
@@ -232,8 +234,6 @@ typedef struct PGXACT
 
    uint8       vacuumFlags;    /* vacuum-related flags, see above */
    bool        overflowed;
-   bool        delayChkpt;     /* true if this proc delays checkpoint start;
-                                * previously called InCommit */
 
    uint8       nxids;
 } PGXACT;