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Tweak dynahash.c to not allocate so many entries at once when dealing

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with a table that has a small predicted size.  Avoids wasting several
hundred K on the timezone hash table, which is likely to have only one
or a few entries, but the entries use up 10Kb apiece ...
This commit is contained in:
Tom Lane 2005-06-26 23:32:34 +00:00
parent 943b396245
commit 06ae88a82e
3 changed files with 22 additions and 13 deletions
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24
src/backend/utils/hash/dynahash.c
View File

@ -9,7 +9,7 @@
* *
* *
* IDENTIFICATION * IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/utils/hash/dynahash.c,v 1.62 2005/06/18 20:51:30 tgl Exp $ * $PostgreSQL: pgsql/src/backend/utils/hash/dynahash.c,v 1.63 2005/06/26 23:32:33 tgl Exp $
* *
*------------------------------------------------------------------------- *-------------------------------------------------------------------------
*/ */
@ -311,6 +311,7 @@ init_htab(HTAB *hashp, long nelem)
{ {
HASHHDR *hctl = hashp->hctl; HASHHDR *hctl = hashp->hctl;
HASHSEGMENT *segp; HASHSEGMENT *segp;
long lnbuckets;
int nbuckets; int nbuckets;
int nsegs; int nsegs;
@ -319,9 +320,9 @@ init_htab(HTAB *hashp, long nelem)
* number of buckets. Allocate space for the next greater power of * number of buckets. Allocate space for the next greater power of
* two number of buckets * two number of buckets
*/ */
nelem = (nelem - 1) / hctl->ffactor + 1; lnbuckets = (nelem - 1) / hctl->ffactor + 1;
nbuckets = 1 << my_log2(nelem); nbuckets = 1 << my_log2(lnbuckets);
hctl->max_bucket = hctl->low_mask = nbuckets - 1; hctl->max_bucket = hctl->low_mask = nbuckets - 1;
hctl->high_mask = (nbuckets << 1) - 1; hctl->high_mask = (nbuckets << 1) - 1;
@ -363,6 +364,10 @@ init_htab(HTAB *hashp, long nelem)
return false; return false;
} }
/* Choose number of entries to allocate at a time */
hctl->nelem_alloc = (int) Min(nelem, HASHELEMENT_ALLOC_MAX);
hctl->nelem_alloc = Max(hctl->nelem_alloc, 1);
#if HASH_DEBUG #if HASH_DEBUG
fprintf(stderr, "init_htab:\n%s%p\n%s%ld\n%s%ld\n%s%d\n%s%ld\n%s%u\n%s%x\n%s%x\n%s%ld\n%s%ld\n", fprintf(stderr, "init_htab:\n%s%p\n%s%ld\n%s%ld\n%s%d\n%s%ld\n%s%u\n%s%x\n%s%x\n%s%ld\n%s%ld\n",
"TABLE POINTER ", hashp, "TABLE POINTER ", hashp,
@ -394,7 +399,8 @@ hash_estimate_size(long num_entries, Size entrysize)
nSegments, nSegments,
nDirEntries, nDirEntries,
nElementAllocs, nElementAllocs,
elementSize; elementSize,
elementAllocCnt;
/* estimate number of buckets wanted */ /* estimate number of buckets wanted */
nBuckets = 1L << my_log2((num_entries - 1) / DEF_FFACTOR + 1); nBuckets = 1L << my_log2((num_entries - 1) / DEF_FFACTOR + 1);
@ -411,10 +417,12 @@ hash_estimate_size(long num_entries, Size entrysize)
size += MAXALIGN(nDirEntries * sizeof(HASHSEGMENT)); size += MAXALIGN(nDirEntries * sizeof(HASHSEGMENT));
/* segments */ /* segments */
size += nSegments * MAXALIGN(DEF_SEGSIZE * sizeof(HASHBUCKET)); size += nSegments * MAXALIGN(DEF_SEGSIZE * sizeof(HASHBUCKET));
/* elements --- allocated in groups of HASHELEMENT_ALLOC_INCR */ /* elements --- allocated in groups of up to HASHELEMENT_ALLOC_MAX */
elementSize = MAXALIGN(sizeof(HASHELEMENT)) + MAXALIGN(entrysize); elementSize = MAXALIGN(sizeof(HASHELEMENT)) + MAXALIGN(entrysize);
nElementAllocs = (num_entries - 1) / HASHELEMENT_ALLOC_INCR + 1; elementAllocCnt = Min(num_entries, HASHELEMENT_ALLOC_MAX);
size += nElementAllocs * HASHELEMENT_ALLOC_INCR * elementSize; elementAllocCnt = Max(elementAllocCnt, 1);
nElementAllocs = (num_entries - 1) / elementAllocCnt + 1;
size += nElementAllocs * elementAllocCnt * elementSize;
return size; return size;
} }
@ -633,7 +641,7 @@ hash_search(HTAB *hashp,
if (currBucket == NULL) if (currBucket == NULL)
{ {
/* no free elements. allocate another chunk of buckets */ /* no free elements. allocate another chunk of buckets */
if (!element_alloc(hashp, HASHELEMENT_ALLOC_INCR)) if (!element_alloc(hashp, hctl->nelem_alloc))
{ {
/* out of memory */ /* out of memory */
if (action == HASH_ENTER_NULL) if (action == HASH_ENTER_NULL)

7
src/include/utils/hsearch.h
View File

@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California * Portions Copyright (c) 1994, Regents of the University of California
* *
* $PostgreSQL: pgsql/src/include/utils/hsearch.h,v 1.38 2005/06/18 20:51:30 tgl Exp $ * $PostgreSQL: pgsql/src/include/utils/hsearch.h,v 1.39 2005/06/26 23:32:34 tgl Exp $
* *
*------------------------------------------------------------------------- *-------------------------------------------------------------------------
*/ */
@ -97,6 +97,7 @@ typedef struct HASHHDR
Size entrysize; /* total user element size in bytes */ Size entrysize; /* total user element size in bytes */
long max_dsize; /* 'dsize' limit if directory is fixed long max_dsize; /* 'dsize' limit if directory is fixed
* size */ * size */
int nelem_alloc; /* number of entries to allocate at once */
HASHELEMENT *freeList; /* linked list of free elements */ HASHELEMENT *freeList; /* linked list of free elements */
#ifdef HASH_STATISTICS #ifdef HASH_STATISTICS
long accesses; long accesses;
@ -158,8 +159,8 @@ typedef struct HASHCTL
/* max_dsize value to indicate expansible directory */ /* max_dsize value to indicate expansible directory */
#define NO_MAX_DSIZE (-1) #define NO_MAX_DSIZE (-1)
/* number of hash elements allocated at once */ /* max number of hash elements allocated at once */
#define HASHELEMENT_ALLOC_INCR (32) #define HASHELEMENT_ALLOC_MAX (32)
/* hash_search operations */ /* hash_search operations */
typedef enum typedef enum

4
src/timezone/pgtz.c
View File

@ -6,7 +6,7 @@
* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
* *
* IDENTIFICATION * IDENTIFICATION
* $PostgreSQL: pgsql/src/timezone/pgtz.c,v 1.35 2005/06/20 08:00:51 neilc Exp $ * $PostgreSQL: pgsql/src/timezone/pgtz.c,v 1.36 2005/06/26 23:32:34 tgl Exp $
* *
*------------------------------------------------------------------------- *-------------------------------------------------------------------------
*/ */
@ -978,7 +978,7 @@ init_timezone_hashtable(void)
hash_ctl.entrysize = sizeof(pg_tz); hash_ctl.entrysize = sizeof(pg_tz);
timezone_cache = hash_create("Timezones", timezone_cache = hash_create("Timezones",
31, 4,
&hash_ctl, &hash_ctl,
HASH_ELEM); HASH_ELEM);
if (!timezone_cache) if (!timezone_cache)