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Commit20cb18d

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Make catalog cache hash tables resizeable.
If the hash table backing a catalog cache becomes too full (fillfactor > 2),enlarge it. A new buckets array, double the size of the old, is allocated,and all entries in the old hash are moved to the right bucket in the newhash.This has two benefits. First, cache lookups don't get so expensive whenthere are lots of entries in a cache, like if you access hundreds ofthousands of tables. Second, we can make the (initial) sizes of the cachesmuch smaller, which saves memory.This patch dials down the initial sizes of the catcaches. The new sizes arechosen so that a backend that only runs a few basic queries still won't needto enlarge any of them.
1 parentb1892aa commit20cb18d

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3 files changed

+102
-58
lines changed

3 files changed

+102
-58
lines changed

‎src/backend/utils/cache/catcache.c

Lines changed: 48 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -734,9 +734,8 @@ InitCatCache(int id,
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inti;
735735

736736
/*
737-
* nbuckets is the number of hash buckets to use in this catcache.
738-
* Currently we just use a hard-wired estimate of an appropriate size for
739-
* each cache; maybe later make them dynamically resizable?
737+
* nbuckets is the initial number of hash buckets to use in this catcache.
738+
* It will be enlarged later if it becomes too full.
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*
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* nbuckets must be a power of two. We check this via Assert rather than
742741
* a full runtime check because the values will be coming from constant
@@ -775,7 +774,8 @@ InitCatCache(int id,
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*
776775
* Note: we rely on zeroing to initialize all the dlist headers correctly
777776
*/
778-
cp= (CatCache*)palloc0(sizeof(CatCache)+nbuckets*sizeof(dlist_head));
777+
cp= (CatCache*)palloc0(sizeof(CatCache));
778+
cp->cc_bucket=palloc0(nbuckets*sizeof(dlist_head));
779779

780780
/*
781781
* initialize the cache's relation information for the relation
@@ -813,6 +813,43 @@ InitCatCache(int id,
813813
returncp;
814814
}
815815

816+
/*
817+
* Enlarge a catcache, doubling the number of buckets.
818+
*/
819+
staticvoid
820+
RehashCatCache(CatCache*cp)
821+
{
822+
dlist_head*newbucket;
823+
intnewnbuckets;
824+
inti;
825+
826+
elog(DEBUG1,"rehashing catalog cache id %d for %s; %d tups, %d buckets",
827+
cp->id,cp->cc_relname,cp->cc_ntup,cp->cc_nbuckets);
828+
829+
/* Allocate a new, larger, hash table. */
830+
newnbuckets=cp->cc_nbuckets*2;
831+
newbucket= (dlist_head*)MemoryContextAllocZero(CacheMemoryContext,newnbuckets*sizeof(dlist_head));
832+
833+
/* Move all entries from old hash table to new. */
834+
for (i=0;i<cp->cc_nbuckets;i++)
835+
{
836+
dlist_mutable_iteriter;
837+
dlist_foreach_modify(iter,&cp->cc_bucket[i])
838+
{
839+
CatCTup*ct=dlist_container(CatCTup,cache_elem,iter.cur);
840+
inthashIndex=HASH_INDEX(ct->hash_value,newnbuckets);
841+
842+
dlist_delete(iter.cur);
843+
dlist_push_head(&newbucket[hashIndex],&ct->cache_elem);
844+
}
845+
}
846+
847+
/* Switch to the new array. */
848+
pfree(cp->cc_bucket);
849+
cp->cc_nbuckets=newnbuckets;
850+
cp->cc_bucket=newbucket;
851+
}
852+
816853
/*
817854
*CatalogCacheInitializeCache
818855
*
@@ -1684,6 +1721,13 @@ CatalogCacheCreateEntry(CatCache *cache, HeapTuple ntp,
16841721
cache->cc_ntup++;
16851722
CacheHdr->ch_ntup++;
16861723

1724+
/*
1725+
* If the hash table has become too full, enlarge the buckets array.
1726+
* Quite arbitrarily, we enlarge when fill factor > 2.
1727+
*/
1728+
if (cache->cc_ntup>cache->cc_nbuckets*2)
1729+
RehashCatCache(cache);
1730+
16871731
returnct;
16881732
}
16891733

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