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Commitda072ab

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Make some simple performance improvements in TransactionIdIsInProgress().
For XIDs of our own transaction and subtransactions, it's cheaper to askTransactionIdIsCurrentTransactionId() than to look in shared memory.Also, the xids[] work array is always the same size within any givenprocess, so malloc it just once instead of doing a palloc/pfree on everycall; aside from being faster this lets us get rid of some goto's, sincewe no longer have any end-of-function pfree to do. Both ideas by Heikki.
1 parentbd0af82 commitda072ab

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-29
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1 file changed

+46
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lines changed

‎src/backend/storage/ipc/procarray.c‎

Lines changed: 46 additions & 29 deletions
Original file line numberDiff line numberDiff line change
@@ -23,7 +23,7 @@
2323
*
2424
*
2525
* IDENTIFICATION
26-
* $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.33 2007/09/08 20:31:15 tgl Exp $
26+
* $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.34 2007/09/21 17:36:53 tgl Exp $
2727
*
2828
*-------------------------------------------------------------------------
2929
*/
@@ -60,11 +60,13 @@ static ProcArrayStruct *procArray;
6060

6161
/* counters for XidCache measurement */
6262
staticlongxc_by_recent_xmin=0;
63+
staticlongxc_by_my_xact=0;
6364
staticlongxc_by_main_xid=0;
6465
staticlongxc_by_child_xid=0;
6566
staticlongxc_slow_answer=0;
6667

6768
#definexc_by_recent_xmin_inc()(xc_by_recent_xmin++)
69+
#definexc_by_my_xact_inc()(xc_by_my_xact++)
6870
#definexc_by_main_xid_inc()(xc_by_main_xid++)
6971
#definexc_by_child_xid_inc()(xc_by_child_xid++)
7072
#definexc_slow_answer_inc()(xc_slow_answer++)
@@ -73,6 +75,7 @@ static void DisplayXidCache(void);
7375
#else/* !XIDCACHE_DEBUG */
7476

7577
#definexc_by_recent_xmin_inc()((void) 0)
78+
#definexc_by_my_xact_inc()((void) 0)
7679
#definexc_by_main_xid_inc()((void) 0)
7780
#definexc_by_child_xid_inc()((void) 0)
7881
#definexc_slow_answer_inc()((void) 0)
@@ -320,14 +323,12 @@ ProcArrayClearTransaction(PGPROC *proc)
320323
bool
321324
TransactionIdIsInProgress(TransactionIdxid)
322325
{
323-
boolresult= false;
326+
staticTransactionId*xids=NULL;
327+
intnxids=0;
324328
ProcArrayStruct*arrayP=procArray;
329+
TransactionIdtopxid;
325330
inti,
326331
j;
327-
intnxids=0;
328-
TransactionId*xids;
329-
TransactionIdtopxid;
330-
boollocked;
331332

332333
/*
333334
* Don't bother checking a transaction older than RecentXmin; it could not
@@ -341,18 +342,43 @@ TransactionIdIsInProgress(TransactionId xid)
341342
return false;
342343
}
343344

344-
/* Get workspace to remember main XIDs in */
345-
xids= (TransactionId*)palloc(sizeof(TransactionId)*arrayP->maxProcs);
345+
/*
346+
* Also, we can handle our own transaction (and subtransactions) without
347+
* any access to shared memory.
348+
*/
349+
if (TransactionIdIsCurrentTransactionId(xid))
350+
{
351+
xc_by_my_xact_inc();
352+
return true;
353+
}
354+
355+
/*
356+
* If not first time through, get workspace to remember main XIDs in.
357+
* We malloc it permanently to avoid repeated palloc/pfree overhead.
358+
*/
359+
if (xids==NULL)
360+
{
361+
xids= (TransactionId*)
362+
malloc(arrayP->maxProcs*sizeof(TransactionId));
363+
if (xids==NULL)
364+
ereport(ERROR,
365+
(errcode(ERRCODE_OUT_OF_MEMORY),
366+
errmsg("out of memory")));
367+
}
346368

347369
LWLockAcquire(ProcArrayLock,LW_SHARED);
348-
locked= true;
349370

350371
for (i=0;i<arrayP->numProcs;i++)
351372
{
352373
volatilePGPROC*proc=arrayP->procs[i];
374+
TransactionIdpxid;
375+
376+
/* Ignore my own proc --- dealt with it above */
377+
if (proc==MyProc)
378+
continue;
353379

354380
/* Fetch xid just once - see GetNewTransactionId */
355-
TransactionIdpxid=proc->xid;
381+
pxid=proc->xid;
356382

357383
if (!TransactionIdIsValid(pxid))
358384
continue;
@@ -362,9 +388,9 @@ TransactionIdIsInProgress(TransactionId xid)
362388
*/
363389
if (TransactionIdEquals(pxid,xid))
364390
{
391+
LWLockRelease(ProcArrayLock);
365392
xc_by_main_xid_inc();
366-
result= true;
367-
gotoresult_known;
393+
return true;
368394
}
369395

370396
/*
@@ -384,9 +410,9 @@ TransactionIdIsInProgress(TransactionId xid)
384410

385411
if (TransactionIdEquals(cxid,xid))
386412
{
413+
LWLockRelease(ProcArrayLock);
387414
xc_by_child_xid_inc();
388-
result= true;
389-
gotoresult_known;
415+
return true;
390416
}
391417
}
392418

@@ -402,14 +428,13 @@ TransactionIdIsInProgress(TransactionId xid)
402428
}
403429

404430
LWLockRelease(ProcArrayLock);
405-
locked= false;
406431

407432
/*
408433
* If none of the relevant caches overflowed, we know the Xid is not
409434
* running without looking at pg_subtrans.
410435
*/
411436
if (nxids==0)
412-
gotoresult_known;
437+
return false;
413438

414439
/*
415440
* Step 3: have to check pg_subtrans.
@@ -422,7 +447,7 @@ TransactionIdIsInProgress(TransactionId xid)
422447
xc_slow_answer_inc();
423448

424449
if (TransactionIdDidAbort(xid))
425-
gotoresult_known;
450+
return false;
426451

427452
/*
428453
* It isn't aborted, so check whether the transaction tree it belongs to
@@ -436,20 +461,11 @@ TransactionIdIsInProgress(TransactionId xid)
436461
for (i=0;i<nxids;i++)
437462
{
438463
if (TransactionIdEquals(xids[i],topxid))
439-
{
440-
result= true;
441-
break;
442-
}
464+
return true;
443465
}
444466
}
445467

446-
result_known:
447-
if (locked)
448-
LWLockRelease(ProcArrayLock);
449-
450-
pfree(xids);
451-
452-
returnresult;
468+
return false;
453469
}
454470

455471
/*
@@ -1284,8 +1300,9 @@ static void
12841300
DisplayXidCache(void)
12851301
{
12861302
fprintf(stderr,
1287-
"XidCache: xmin: %ld, mainxid: %ld, childxid: %ld, slow: %ld\n",
1303+
"XidCache: xmin: %ld,myxact: %ld,mainxid: %ld, childxid: %ld, slow: %ld\n",
12881304
xc_by_recent_xmin,
1305+
xc_by_my_xact,
12891306
xc_by_main_xid,
12901307
xc_by_child_xid,
12911308
xc_slow_answer);

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