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snapshot scalability: Move subxact info to ProcGlobal, remove PGXACT.

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Similar to the previous changes this increases the chance that data
frequently needed by GetSnapshotData() stays in l2 cache. In many
workloads subtransactions are very rare, and this makes the check for
that considerably cheaper.

As this removes the last member of PGXACT, there is no need to keep it
around anymore.

On a larger 2 socket machine this and the two preceding commits result
in a ~1.07x performance increase in read-only pgbench. For read-heavy
mixed r/w workloads without row level contention, I see about 1.1x.

Author: Andres Freund <andres@anarazel.de>
Reviewed-By: Robert Haas <robertmhaas@gmail.com>
Reviewed-By: Thomas Munro <thomas.munro@gmail.com>
Reviewed-By: David Rowley <dgrowleyml@gmail.com>
Discussion: https://postgr.es/m/20200301083601.ews6hz5dduc3w2se@alap3.anarazel.de
This commit is contained in:
Andres Freund
2020-08-14 14:30:38 -07:00
parent 5788e258bb
commit 73487a60fc
7 changed files with 113 additions and 113 deletions
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7
src/backend/access/transam/clog.c
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@ -295,7 +295,7 @@ TransactionIdSetPageStatus(TransactionId xid, int nsubxids,
*/
if (all_xact_same_page && xid == MyProc->xid &&
nsubxids <= THRESHOLD_SUBTRANS_CLOG_OPT &&
nsubxids == MyPgXact->nxids &&
nsubxids == MyProc->subxidStatus.count &&
memcmp(subxids, MyProc->subxids.xids,
nsubxids * sizeof(TransactionId)) == 0)
{
@ -510,16 +510,15 @@ TransactionGroupUpdateXidStatus(TransactionId xid, XidStatus status,
while (nextidx != INVALID_PGPROCNO)
{
PGPROC *proc = &ProcGlobal->allProcs[nextidx];
PGXACT *pgxact = &ProcGlobal->allPgXact[nextidx];
/*
* Transactions with more than THRESHOLD_SUBTRANS_CLOG_OPT sub-XIDs
* should not use group XID status update mechanism.
*/
Assert(pgxact->nxids <= THRESHOLD_SUBTRANS_CLOG_OPT);
Assert(proc->subxidStatus.count <= THRESHOLD_SUBTRANS_CLOG_OPT);
TransactionIdSetPageStatusInternal(proc->clogGroupMemberXid,
pgxact->nxids,
proc->subxidStatus.count,
proc->subxids.xids,
proc->clogGroupMemberXidStatus,
proc->clogGroupMemberLsn,