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Move "hot" members of PGPROC into a separate PGXACT array.

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This speeds up snapshot-taking and reduces ProcArrayLock contention.
Also, the PGPROC (and PGXACT) structures used by two-phase commit are
now allocated as part of the main array, rather than in a separate
array, and we keep ProcArray sorted in pointer order.  These changes
are intended to minimize the number of cache lines that must be pulled
in to take a snapshot, and testing shows a substantial increase in
performance on both read and write workloads at high concurrencies.

Pavan Deolasee, Heikki Linnakangas, Robert Haas
This commit is contained in:
Robert Haas
2011-11-25 08:02:10 -05:00
parent 9ed439a9c0
commit ed0b409d22
14 changed files with 356 additions and 208 deletions
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11
src/backend/access/transam/varsup.c
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@ -54,7 +54,7 @@ GetNewTransactionId(bool isSubXact)
if (IsBootstrapProcessingMode())
{
Assert(!isSubXact);
MyProc->xid = BootstrapTransactionId;
MyPgXact->xid = BootstrapTransactionId;
return BootstrapTransactionId;
}
@ -208,20 +208,21 @@ GetNewTransactionId(bool isSubXact)
* TransactionId and int fetch/store are atomic.
*/
volatile PGPROC *myproc = MyProc;
volatile PGXACT *mypgxact = MyPgXact;
if (!isSubXact)
myproc->xid = xid;
mypgxact->xid = xid;
else
{
int nxids = myproc->subxids.nxids;
int nxids = mypgxact->nxids;
if (nxids < PGPROC_MAX_CACHED_SUBXIDS)
{
myproc->subxids.xids[nxids] = xid;
myproc->subxids.nxids = nxids + 1;
mypgxact->nxids = nxids + 1;
}
else
myproc->subxids.overflowed = true;
mypgxact->overflowed = true;
}
}