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Avoid searching for the target catcache in CatalogCacheIdInvalidate.

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A test case provided by Mathieu Fenniak shows that the initial search for
the target catcache in CatalogCacheIdInvalidate consumes a very significant
amount of overhead in cases where cache invalidation is triggered but has
little useful work to do.  There is no good reason for that search to exist
at all, as the index array maintained by syscache.c allows direct lookup of
the catcache from its ID.  We just need a frontend function in syscache.c,
matching the division of labor for most other cache-accessing operations.

While there's more that can be done in this area, this patch alone reduces
the runtime of Mathieu's example by 2X.  We can hope that it offers some
useful benefit in other cases too, although usually cache invalidation
overhead is not such a striking fraction of the total runtime.

Back-patch to 9.4 where logical decoding was introduced.  It might be
worth going further back, but presently the only case we know of where
cache invalidation is really a significant burden is in logical decoding.
Also, older branches have fewer catcaches, reducing the possible benefit.

(Note: although this nominally changes catcache's API, we have always
documented CatalogCacheIdInvalidate as a private function, so I would
have little sympathy for an external module calling it directly.  So
backpatching should be fine.)

Discussion: https://postgr.es/m/CAHoiPjzea6N0zuCi=+f9v_j94nfsy6y8SU7-=bp4=7qw6_i=Rg@mail.gmail.com
This commit is contained in:
Tom Lane
2017-05-12 18:17:29 -04:00
parent 928c4de309
commit 50ee1c7462
5 changed files with 65 additions and 56 deletions
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21
src/backend/utils/cache/syscache.c vendored
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@ -1338,6 +1338,27 @@ SearchSysCacheList(int cacheId, int nkeys,
key1, key2, key3, key4);
}
/*
* SysCacheInvalidate
*
* Invalidate entries in the specified cache, given a hash value.
* See CatCacheInvalidate() for more info.
*
* This routine is only quasi-public: it should only be used by inval.c.
*/
void
SysCacheInvalidate(int cacheId, uint32 hashValue)
{
if (cacheId < 0 || cacheId >= SysCacheSize)
elog(ERROR, "invalid cache ID: %d", cacheId);
/* if this cache isn't initialized yet, no need to do anything */
if (!PointerIsValid(SysCache[cacheId]))
return;
CatCacheInvalidate(SysCache[cacheId], hashValue);
}
/*
* Certain relations that do not have system caches send snapshot invalidation
* messages in lieu of catcache messages. This is for the benefit of