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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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63
src/include/utils/hsearch.h
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@@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $Id: hsearch.h,v 1.28 2003/08/04 02:40:15 momjian Exp $
* $Id: hsearch.h,v 1.29 2003/08/19 01:13:41 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -15,6 +15,23 @@
#define HSEARCH_H
/*
* Hash and comparison functions must have these signatures. Comparison
* functions return zero for match, nonzero for no match. (The comparison
* function definition is designed to allow memcmp() and strncmp() to be
* used directly as key comparison functions.)
*/
typedef uint32 (*HashValueFunc) (const void *key, Size keysize);
typedef int (*HashCompareFunc) (const void *key1, const void *key2,
Size keysize);
/*
* Space allocation function for a hashtable --- designed to match malloc().
* Note: there is no free function API; can't destroy a hashtable unless you
* use the default allocator.
*/
typedef void *(*HashAllocFunc) (Size request);
/*
* Constants
*
@@ -44,6 +61,7 @@
typedef struct HASHELEMENT
{
struct HASHELEMENT *link; /* link to next entry in same bucket */
uint32 hashvalue; /* hash function result for this entry */
} HASHELEMENT;
/* A hash bucket is a linked list of HASHELEMENTs */
@@ -64,8 +82,8 @@ typedef struct HASHHDR
long ffactor; /* Fill factor */
long nentries; /* Number of entries in hash table */
long nsegs; /* Number of allocated segments */
long keysize; /* hash key length in bytes */
long entrysize; /* total user element size in bytes */
Size keysize; /* hash key length in bytes */
Size entrysize; /* total user element size in bytes */
long max_dsize; /* 'dsize' limit if directory is fixed
* size */
HASHELEMENT *freeList; /* linked list of free elements */
@@ -83,8 +101,9 @@ typedef struct HTAB
{
HASHHDR *hctl; /* shared control information */
HASHSEGMENT *dir; /* directory of segment starts */
uint32 (*hash) (void *key, int keysize); /* Hash Function */
void *(*alloc) (Size); /* memory allocator */
HashValueFunc hash; /* hash function */
HashCompareFunc match; /* key comparison function */
HashAllocFunc alloc; /* memory allocator */
MemoryContext hcxt; /* memory context if default allocator
* used */
char *tabname; /* table name (for error messages) */
@@ -97,28 +116,30 @@ typedef struct HASHCTL
{
long ssize; /* Segment Size */
long dsize; /* (initial) Directory Size */
long ffactor; /* Fill factor */
uint32 (*hash) (void *key, int keysize); /* Hash Function */
long keysize; /* hash key length in bytes */
long entrysize; /* total user element size in bytes */
long max_dsize; /* limit to dsize if directory size is
* limited */
void *(*alloc) (Size); /* memory allocation function */
long ffactor; /* Fill factor */
Size keysize; /* hash key length in bytes */
Size entrysize; /* total user element size in bytes */
HashValueFunc hash; /* hash function */
HashCompareFunc match; /* key comparison function */
HashAllocFunc alloc; /* memory allocator */
HASHSEGMENT *dir; /* directory of segment starts */
HASHHDR *hctl; /* location of header in shared mem */
MemoryContext hcxt; /* memory context to use for allocations */
} HASHCTL;
/* Flags to indicate which parameters are supplied */
#define HASH_SEGMENT 0x002 /* Setting segment size */
#define HASH_DIRSIZE 0x004 /* Setting directory size */
#define HASH_FFACTOR 0x008 /* Setting fill factor */
#define HASH_SEGMENT 0x002 /* Set segment size */
#define HASH_DIRSIZE 0x004 /* Set directory size */
#define HASH_FFACTOR 0x008 /* Set fill factor */
#define HASH_FUNCTION 0x010 /* Set user defined hash function */
#define HASH_ELEM 0x020 /* Setting key/entry size */
#define HASH_SHARED_MEM 0x040 /* Setting shared mem const */
#define HASH_ELEM 0x020 /* Set key/entry size */
#define HASH_SHARED_MEM 0x040 /* Set shared mem const */
#define HASH_ATTACH 0x080 /* Do not initialize hctl */
#define HASH_ALLOC 0x100 /* Setting memory allocator */
#define HASH_CONTEXT 0x200 /* Setting explicit memory context */
#define HASH_ALLOC 0x100 /* Set memory allocator */
#define HASH_CONTEXT 0x200 /* Set explicit memory context */
#define HASH_COMPARE 0x400 /* Set user defined comparison function */
/* max_dsize value to indicate expansible directory */
@@ -151,17 +172,17 @@ extern HTAB *hash_create(const char *tabname, long nelem,
HASHCTL *info, int flags);
extern void hash_destroy(HTAB *hashp);
extern void hash_stats(const char *where, HTAB *hashp);
extern void *hash_search(HTAB *hashp, void *keyPtr, HASHACTION action,
extern void *hash_search(HTAB *hashp, const void *keyPtr, HASHACTION action,
bool *foundPtr);
extern void hash_seq_init(HASH_SEQ_STATUS *status, HTAB *hashp);
extern void *hash_seq_search(HASH_SEQ_STATUS *status);
extern long hash_estimate_size(long num_entries, long entrysize);
extern long hash_estimate_size(long num_entries, Size entrysize);
extern long hash_select_dirsize(long num_entries);
/*
* prototypes for functions in hashfn.c
*/
extern uint32 string_hash(void *key, int keysize);
extern uint32 tag_hash(void *key, int keysize);
extern uint32 string_hash(const void *key, Size keysize);
extern uint32 tag_hash(const void *key, Size keysize);
#endif /* HSEARCH_H */