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Improve dynahash.c's API so that caller can specify the comparison function

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as well as the hash function (formerly the comparison function was hardwired
as memcmp()).  This makes it possible to eliminate the special-purpose
hashtable management code in execGrouping.c in favor of using dynahash to
manage tuple hashtables; which is a win because dynahash knows how to expand
a hashtable when the original size estimate was too small, whereas the
special-purpose code was too stupid to do that.  (See recent gripe from
Stephan Szabo about poor performance when hash table size estimate is way
off.)  Free side benefit: when using string_hash, the default comparison
function is now strncmp() instead of memcmp().  This should eliminate some
part of the overhead associated with larger NAMEDATALEN values.
This commit is contained in:
Tom Lane
2003-08-19 01:13:41 +00:00
parent 23e10843db
commit 80860c32d9
9 changed files with 263 additions and 194 deletions
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82
src/backend/utils/hash/dynahash.c
View File

@@ -9,7 +9,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/utils/hash/dynahash.c,v 1.47 2003/08/04 02:40:06 momjian Exp $
* $Header: /cvsroot/pgsql/src/backend/utils/hash/dynahash.c,v 1.48 2003/08/19 01:13:41 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -44,7 +44,6 @@
#include "postgres.h"
#include "utils/dynahash.h"
#include "utils/hsearch.h"
#include "utils/memutils.h"
@@ -63,7 +62,6 @@
* Private function prototypes
*/
static void *DynaHashAlloc(Size size);
static uint32 call_hash(HTAB *hashp, void *k);
static HASHSEGMENT seg_alloc(HTAB *hashp);
static bool element_alloc(HTAB *hashp);
static bool dir_realloc(HTAB *hashp);
@@ -133,6 +131,19 @@ hash_create(const char *tabname, long nelem, HASHCTL *info, int flags)
else
hashp->hash = string_hash; /* default hash function */
/*
* If you don't specify a match function, it defaults to strncmp() if
* you used string_hash (either explicitly or by default) and to
* memcmp() otherwise. (Prior to PostgreSQL 7.4, memcmp() was always
* used.)
*/
if (flags & HASH_COMPARE)
hashp->match = info->match;
else if (hashp->hash == string_hash)
hashp->match = (HashCompareFunc) strncmp;
else
hashp->match = memcmp;
if (flags & HASH_SHARED_MEM)
{
/*
@@ -155,7 +166,7 @@ hash_create(const char *tabname, long nelem, HASHCTL *info, int flags)
hashp->hctl = NULL;
hashp->dir = NULL;
hashp->alloc = MEM_ALLOC;
hashp->hcxt = DynaHashCxt;
hashp->hcxt = CurrentDynaHashCxt;
hashp->isshared = false;
}
@@ -207,26 +218,13 @@ hash_create(const char *tabname, long nelem, HASHCTL *info, int flags)
hashp->alloc = info->alloc;
else
{
if (flags & HASH_CONTEXT)
{
/* hash table structures live in child of given context */
CurrentDynaHashCxt = AllocSetContextCreate(info->hcxt,
"DynaHashTable",
ALLOCSET_DEFAULT_MINSIZE,
ALLOCSET_DEFAULT_INITSIZE,
ALLOCSET_DEFAULT_MAXSIZE);
hashp->hcxt = CurrentDynaHashCxt;
}
else
{
/* hash table structures live in child of DynaHashCxt */
CurrentDynaHashCxt = AllocSetContextCreate(DynaHashCxt,
"DynaHashTable",
ALLOCSET_DEFAULT_MINSIZE,
ALLOCSET_DEFAULT_INITSIZE,
ALLOCSET_DEFAULT_MAXSIZE);
hashp->hcxt = CurrentDynaHashCxt;
}
/* remaining hash table structures live in child of given context */
hashp->hcxt = AllocSetContextCreate(CurrentDynaHashCxt,
"DynaHashTable",
ALLOCSET_DEFAULT_MINSIZE,
ALLOCSET_DEFAULT_INITSIZE,
ALLOCSET_DEFAULT_MAXSIZE);
CurrentDynaHashCxt = hashp->hcxt;
}
if (!init_htab(hashp, nelem))
@@ -351,7 +349,7 @@ init_htab(HTAB *hashp, long nelem)
* NB: assumes that all hash structure parameters have default values!
*/
long
hash_estimate_size(long num_entries, long entrysize)
hash_estimate_size(long num_entries, Size entrysize)
{
long size = 0;
long nBuckets,
@@ -447,7 +445,6 @@ void
hash_stats(const char *where, HTAB *hashp)
{
#if HASH_STATISTICS
fprintf(stderr, "%s: this HTAB -- accesses %ld collisions %ld\n",
where, hashp->hctl->accesses, hashp->hctl->collisions);
@@ -459,19 +456,16 @@ hash_stats(const char *where, HTAB *hashp)
fprintf(stderr, "hash_stats: total expansions %ld\n",
hash_expansions);
#endif
}
/*******************************SEARCH ROUTINES *****************************/
static uint32
call_hash(HTAB *hashp, void *k)
{
HASHHDR *hctl = hashp->hctl;
uint32 hash_val,
bucket;
hash_val = hashp->hash(k, (int) hctl->keysize);
/* Convert a hash value to a bucket number */
static inline uint32
calc_bucket(HASHHDR *hctl, uint32 hash_val)
{
uint32 bucket;
bucket = hash_val & hctl->high_mask;
if (bucket > hctl->max_bucket)
@@ -506,11 +500,12 @@ call_hash(HTAB *hashp, void *k)
*/
void *
hash_search(HTAB *hashp,
void *keyPtr,
const void *keyPtr,
HASHACTION action,
bool *foundPtr)
{
HASHHDR *hctl = hashp->hctl;
uint32 hashvalue = 0;
uint32 bucket;
long segment_num;
long segment_ndx;
@@ -545,7 +540,12 @@ hash_search(HTAB *hashp,
}
else
{
bucket = call_hash(hashp, keyPtr);
HashCompareFunc match;
Size keysize = hctl->keysize;
hashvalue = hashp->hash(keyPtr, keysize);
bucket = calc_bucket(hctl, hashvalue);
segment_num = bucket >> hctl->sshift;
segment_ndx = MOD(bucket, hctl->ssize);
@@ -560,9 +560,11 @@ hash_search(HTAB *hashp,
/*
* Follow collision chain looking for matching key
*/
match = hashp->match; /* save one fetch in inner loop */
while (currBucket != NULL)
{
if (memcmp(ELEMENTKEY(currBucket), keyPtr, hctl->keysize) == 0)
if (currBucket->hashvalue == hashvalue &&
match(ELEMENTKEY(currBucket), keyPtr, keysize) == 0)
break;
prevBucketPtr = &(currBucket->link);
currBucket = *prevBucketPtr;
@@ -641,6 +643,7 @@ hash_search(HTAB *hashp,
currBucket->link = NULL;
/* copy key into record */
currBucket->hashvalue = hashvalue;
memcpy(ELEMENTKEY(currBucket), keyPtr, hctl->keysize);
/* caller is expected to fill the data field on return */
@@ -802,7 +805,7 @@ expand_table(HTAB *hashp)
/*
* Relocate records to the new bucket. NOTE: because of the way the
* hash masking is done in call_hash, only one old bucket can need to
* hash masking is done in calc_bucket, only one old bucket can need to
* be split at this point. With a different way of reducing the hash
* value, that might not be true!
*/
@@ -820,8 +823,7 @@ expand_table(HTAB *hashp)
currElement = nextElement)
{
nextElement = currElement->link;
if ((long) call_hash(hashp, (void *) ELEMENTKEY(currElement))
== old_bucket)
if ((long) calc_bucket(hctl, currElement->hashvalue) == old_bucket)
{
*oldlink = currElement;
oldlink = &currElement->link;

17
src/backend/utils/hash/hashfn.c
View File

@@ -9,7 +9,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/utils/hash/hashfn.c,v 1.18 2003/08/04 02:40:06 momjian Exp $
* $Header: /cvsroot/pgsql/src/backend/utils/hash/hashfn.c,v 1.19 2003/08/19 01:13:41 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -22,24 +22,21 @@
/*
* string_hash: hash function for keys that are null-terminated strings.
*
* NOTE: since dynahash.c backs this up with a fixed-length memcmp(),
* the key must actually be zero-padded to the specified maximum length
* to work correctly. However, if it is known that nothing after the
* first zero byte is interesting, this is the right hash function to use.
*
* NOTE: this is the default hash function if none is specified.
*/
uint32
string_hash(void *key, int keysize)
string_hash(const void *key, Size keysize)
{
return DatumGetUInt32(hash_any((unsigned char *) key, strlen((char *) key)));
return DatumGetUInt32(hash_any((const unsigned char *) key,
(int) strlen((const char *) key)));
}
/*
* tag_hash: hash function for fixed-size tag values
*/
uint32
tag_hash(void *key, int keysize)
tag_hash(const void *key, Size keysize)
{
return DatumGetUInt32(hash_any((unsigned char *) key, keysize));
return DatumGetUInt32(hash_any((const unsigned char *) key,
(int) keysize));
}