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Commitbe0a666

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Remove large fill factor support from dynahash.c.
Since ancient times we have had support for a fill factor (maximum loadfactor) to be set for a dynahash hash table, but:1. It was an integer, whereas for in-memory hash tables interestingload factor targets are probably somewhere near the 0.75-1.0 range.2. It was implemented in a way that performed an expensive divisionoperation that regularly showed up in profiles.3. We are not aware of anyone ever having used a non-default value.Therefore, remove support, effectively fixing it at 1.Author: Jakub Wartak <Jakub.Wartak@tomtom.com>Reviewed-by: Alvaro Herrera <alvherre@2ndquadrant.com>Reviewed-by: Tomas Vondra <tomas.vondra@2ndquadrant.com>Reviewed-by: Thomas Munro <thomas.munro@gmail.com>Reviewed-by: David Rowley <dgrowleyml@gmail.com>Discussion:https://postgr.es/m/VI1PR0701MB696044FC35013A96FECC7AC8F62D0%40VI1PR0701MB6960.eurprd07.prod.outlook.com
1 parent06a7c31 commitbe0a666

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2 files changed

+6
-16
lines changed

2 files changed

+6
-16
lines changed

‎src/backend/utils/hash/dynahash.c

Lines changed: 6 additions & 14 deletions
Original file line numberDiff line numberDiff line change
@@ -122,7 +122,6 @@
122122
#defineDEF_SEGSIZE 256
123123
#defineDEF_SEGSIZE_SHIFT 8/* must be log2(DEF_SEGSIZE) */
124124
#defineDEF_DIRSIZE 256
125-
#defineDEF_FFACTOR 1/* default fill factor */
126125

127126
/* Number of freelists to be used for a partitioned hash table. */
128127
#defineNUM_FREELISTS32
@@ -191,7 +190,6 @@ struct HASHHDR
191190
Sizekeysize;/* hash key length in bytes */
192191
Sizeentrysize;/* total user element size in bytes */
193192
longnum_partitions;/* # partitions (must be power of 2), or 0 */
194-
longffactor;/* target fill factor */
195193
longmax_dsize;/* 'dsize' limit if directory is fixed size */
196194
longssize;/* segment size --- must be power of 2 */
197195
intsshift;/* segment shift = log2(ssize) */
@@ -497,8 +495,6 @@ hash_create(const char *tabname, long nelem, HASHCTL *info, int flags)
497495
/* ssize had better be a power of 2 */
498496
Assert(hctl->ssize== (1L <<hctl->sshift));
499497
}
500-
if (flags&HASH_FFACTOR)
501-
hctl->ffactor=info->ffactor;
502498

503499
/*
504500
* SHM hash tables have fixed directory size passed by the caller.
@@ -603,8 +599,6 @@ hdefault(HTAB *hashp)
603599

604600
hctl->num_partitions=0;/* not partitioned */
605601

606-
hctl->ffactor=DEF_FFACTOR;
607-
608602
/* table has no fixed maximum size */
609603
hctl->max_dsize=NO_MAX_DSIZE;
610604

@@ -670,11 +664,10 @@ init_htab(HTAB *hashp, long nelem)
670664
SpinLockInit(&(hctl->freeList[i].mutex));
671665

672666
/*
673-
* Divide number of elements by the fill factor to determine a desired
674-
* number of buckets. Allocate space for the next greater power of two
675-
* number of buckets
667+
* Allocate space for the next greater power of two number of buckets,
668+
* assuming a desired maximum load factor of 1.
676669
*/
677-
nbuckets=next_pow2_int((nelem-1) /hctl->ffactor+1);
670+
nbuckets=next_pow2_int(nelem);
678671

679672
/*
680673
* In a partitioned table, nbuckets must be at least equal to
@@ -733,7 +726,6 @@ init_htab(HTAB *hashp, long nelem)
733726
"DIRECTORY SIZE ",hctl->dsize,
734727
"SEGMENT SIZE ",hctl->ssize,
735728
"SEGMENT SHIFT ",hctl->sshift,
736-
"FILL FACTOR ",hctl->ffactor,
737729
"MAX BUCKET ",hctl->max_bucket,
738730
"HIGH MASK ",hctl->high_mask,
739731
"LOW MASK ",hctl->low_mask,
@@ -761,7 +753,7 @@ hash_estimate_size(long num_entries, Size entrysize)
761753
elementAllocCnt;
762754

763755
/* estimate number of buckets wanted */
764-
nBuckets=next_pow2_long((num_entries-1) /DEF_FFACTOR+1);
756+
nBuckets=next_pow2_long(num_entries);
765757
/* # of segments needed for nBuckets */
766758
nSegments=next_pow2_long((nBuckets-1) /DEF_SEGSIZE+1);
767759
/* directory entries */
@@ -804,7 +796,7 @@ hash_select_dirsize(long num_entries)
804796
nDirEntries;
805797

806798
/* estimate number of buckets wanted */
807-
nBuckets=next_pow2_long((num_entries-1) /DEF_FFACTOR+1);
799+
nBuckets=next_pow2_long(num_entries);
808800
/* # of segments needed for nBuckets */
809801
nSegments=next_pow2_long((nBuckets-1) /DEF_SEGSIZE+1);
810802
/* directory entries */
@@ -975,7 +967,7 @@ hash_search_with_hash_value(HTAB *hashp,
975967
* order of these tests is to try to check cheaper conditions first.
976968
*/
977969
if (!IS_PARTITIONED(hctl)&& !hashp->frozen&&
978-
hctl->freeList[0].nentries/ (long) (hctl->max_bucket+1) >=hctl->ffactor&&
970+
hctl->freeList[0].nentries> (long) (hctl->max_bucket+1)&&
979971
!has_seq_scans(hashp))
980972
(void)expand_table(hashp);
981973
}

‎src/include/utils/hsearch.h

Lines changed: 0 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -68,7 +68,6 @@ typedef struct HASHCTL
6868
longssize;/* segment size */
6969
longdsize;/* (initial) directory size */
7070
longmax_dsize;/* limit to dsize if dir size is limited */
71-
longffactor;/* fill factor */
7271
Sizekeysize;/* hash key length in bytes */
7372
Sizeentrysize;/* total user element size in bytes */
7473
HashValueFunchash;/* hash function */
@@ -83,7 +82,6 @@ typedef struct HASHCTL
8382
#defineHASH_PARTITION0x0001/* Hashtable is used w/partitioned locking */
8483
#defineHASH_SEGMENT0x0002/* Set segment size */
8584
#defineHASH_DIRSIZE0x0004/* Set directory size (initial and max) */
86-
#defineHASH_FFACTOR0x0008/* Set fill factor */
8785
#defineHASH_ELEM0x0010/* Set keysize and entrysize */
8886
#defineHASH_BLOBS0x0020/* Select support functions for binary keys */
8987
#defineHASH_FUNCTION0x0040/* Set user defined hash function */

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