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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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25
src/include/nodes/execnodes.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: execnodes.h,v 1.103 2003/08/08 21:42:47 momjian Exp $
* $Id: execnodes.h,v 1.104 2003/08/19 01:13:41 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -21,6 +21,7 @@
#include "nodes/bitmapset.h"
#include "nodes/params.h"
#include "nodes/plannodes.h"
#include "utils/hsearch.h"
#include "utils/tuplestore.h"
@ -344,14 +345,14 @@ typedef struct TupleHashTableData *TupleHashTable;
typedef struct TupleHashEntryData
{
TupleHashEntry next; /* next entry in same hash bucket */
uint32 hashkey; /* exact hash key of this entry */
/* firstTuple must be the first field in this struct! */
HeapTuple firstTuple; /* copy of first tuple in this group */
/* there may be additional data beyond the end of this struct */
} TupleHashEntryData; /* VARIABLE LENGTH STRUCT */
typedef struct TupleHashTableData
{
HTAB *hashtab; /* underlying dynahash table */
int numCols; /* number of columns in lookup key */
AttrNumber *keyColIdx; /* attr numbers of key columns */
FmgrInfo *eqfunctions; /* lookup data for comparison functions */
@ -359,19 +360,15 @@ typedef struct TupleHashTableData
MemoryContext tablecxt; /* memory context containing table */
MemoryContext tempcxt; /* context for function evaluations */
Size entrysize; /* actual size to make each hash entry */
int nbuckets; /* number of buckets in hash table */
TupleHashEntry buckets[1]; /* VARIABLE LENGTH ARRAY */
} TupleHashTableData; /* VARIABLE LENGTH STRUCT */
TupleDesc tupdesc; /* tuple descriptor */
} TupleHashTableData;
typedef struct
{
TupleHashEntry next_entry; /* next entry in current chain */
int next_bucket; /* next chain */
} TupleHashIterator;
typedef HASH_SEQ_STATUS TupleHashIterator;
#define ResetTupleHashIterator(iter) \
((iter)->next_entry = NULL, \
(iter)->next_bucket = 0)
#define ResetTupleHashIterator(htable, iter) \
hash_seq_init(iter, (htable)->hashtab)
#define ScanTupleHashTable(iter) \
((TupleHashEntry) hash_seq_search(iter))
/* ----------------------------------------------------------------