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Commit76c23bb

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Reduce overhead of cache-clobber testing in LookupOpclassInfo().
Commit03ffc4d added logic to bypass all caching behavior inLookupOpclassInfo when CLOBBER_CACHE_ALWAYS is enabled. It doesn'tlook like I stopped to think much about what that would cost, butrecent investigation shows that the cost is enormous: it roughlydoubles the time needed for cache-clobber test runs.There does seem to be value in this behavior when trying to testthe opclass-cache loading logic itself, but for other purposes thecost is excessive. Hence, let's back off to doing this only whendebug_invalidate_system_caches_always is at least 3; or in olderbranches, when CLOBBER_CACHE_RECURSIVELY is defined.While here, clean up some other minor issues in LookupOpclassInfo.Re-order the code so we aren't left with broken cache entries (leadingto later core dumps) in the unlikely case that we suffer OOM whiletrying to allocate space for a new entry. (That seems to be myoversight in03ffc4d.) Also, in >= v13, stop allocating one arrayentry too many. That's evidently left over from sloppy reversion in851b14b.Back-patch to all supported branches, mainly to reduce the runtimeof cache-clobbering buildfarm animals.Discussion:https://postgr.es/m/1370856.1625428625@sss.pgh.pa.us
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‎src/backend/utils/cache/relcache.c

Lines changed: 23 additions & 20 deletions
Original file line numberDiff line numberDiff line change
@@ -1597,15 +1597,15 @@ LookupOpclassInfo(Oid operatorClassOid,
15971597
/* First time through: initialize the opclass cache */
15981598
HASHCTLctl;
15991599

1600+
/* Also make sure CacheMemoryContext exists */
1601+
if (!CacheMemoryContext)
1602+
CreateCacheMemoryContext();
1603+
16001604
MemSet(&ctl,0,sizeof(ctl));
16011605
ctl.keysize=sizeof(Oid);
16021606
ctl.entrysize=sizeof(OpClassCacheEnt);
16031607
OpClassCache=hash_create("Operator class cache",64,
16041608
&ctl,HASH_ELEM |HASH_BLOBS);
1605-
1606-
/* Also make sure CacheMemoryContext exists */
1607-
if (!CacheMemoryContext)
1608-
CreateCacheMemoryContext();
16091609
}
16101610

16111611
opcentry= (OpClassCacheEnt*)hash_search(OpClassCache,
@@ -1614,39 +1614,42 @@ LookupOpclassInfo(Oid operatorClassOid,
16141614

16151615
if (!found)
16161616
{
1617-
/*Need to allocate memory for new entry */
1617+
/*Initialize new entry */
16181618
opcentry->valid= false;/* until known OK */
16191619
opcentry->numSupport=numSupport;
1620-
1621-
if (numSupport>0)
1622-
opcentry->supportProcs= (RegProcedure*)
1623-
MemoryContextAllocZero(CacheMemoryContext,
1624-
numSupport*sizeof(RegProcedure));
1625-
else
1626-
opcentry->supportProcs=NULL;
1620+
opcentry->supportProcs=NULL;/* filled below */
16271621
}
16281622
else
16291623
{
16301624
Assert(numSupport==opcentry->numSupport);
16311625
}
16321626

16331627
/*
1634-
* When testing for cache-flush hazards, we intentionally disable the
1635-
* operator class cache and force reloading of the info on each call. This
1636-
* is helpful because we want to test the case where a cache flush occurs
1637-
* while we are loading the info, and it's very hard to provoke that if
1638-
* this happens only once per opclass per backend.
1628+
* When aggressively testing cache-flush hazards, we disable the operator
1629+
* class cache and force reloading of the info on each call. This models
1630+
* no real-world behavior, since the cache entries are never invalidated
1631+
* otherwise. However it can be helpful for detecting bugs in the cache
1632+
* loading logic itself, such as reliance on a non-nailed index. Given
1633+
* the limited use-case and the fact that this adds a great deal of
1634+
* expense, we enable it only in CLOBBER_CACHE_RECURSIVELY mode.
16391635
*/
1640-
#if defined(CLOBBER_CACHE_ALWAYS)
1636+
#if defined(CLOBBER_CACHE_RECURSIVELY)
16411637
opcentry->valid= false;
16421638
#endif
16431639

16441640
if (opcentry->valid)
16451641
returnopcentry;
16461642

16471643
/*
1648-
* Need to fill in new entry.
1649-
*
1644+
* Need to fill in new entry. First allocate space, unless we already did
1645+
* so in some previous attempt.
1646+
*/
1647+
if (opcentry->supportProcs==NULL&&numSupport>0)
1648+
opcentry->supportProcs= (RegProcedure*)
1649+
MemoryContextAllocZero(CacheMemoryContext,
1650+
numSupport*sizeof(RegProcedure));
1651+
1652+
/*
16501653
* To avoid infinite recursion during startup, force heap scans if we're
16511654
* looking up info for the opclasses used by the indexes we would like to
16521655
* reference here.

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