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Remove large fill factor support from dynahash.c.
Since ancient times we have had support for a fill factor (maximum load factor) to be set for a dynahash hash table, but: 1. It was an integer, whereas for in-memory hash tables interesting load factor targets are probably somewhere near the 0.75-1.0 range. 2. It was implemented in a way that performed an expensive division operation 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
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@ -122,7 +122,6 @@
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#define DEF_SEGSIZE 256
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#define DEF_SEGSIZE_SHIFT 8 /* must be log2(DEF_SEGSIZE) */
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#define DEF_DIRSIZE 256
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#define DEF_FFACTOR 1 /* default fill factor */
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/* Number of freelists to be used for a partitioned hash table. */
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#define NUM_FREELISTS 32
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@ -191,7 +190,6 @@ struct HASHHDR
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Size keysize; /* hash key length in bytes */
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Size entrysize; /* total user element size in bytes */
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long num_partitions; /* # partitions (must be power of 2), or 0 */
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long ffactor; /* target fill factor */
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long max_dsize; /* 'dsize' limit if directory is fixed size */
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long ssize; /* segment size --- must be power of 2 */
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int sshift; /* segment shift = log2(ssize) */
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@ -497,8 +495,6 @@ hash_create(const char *tabname, long nelem, HASHCTL *info, int flags)
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/* ssize had better be a power of 2 */
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Assert(hctl->ssize == (1L << hctl->sshift));
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}
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if (flags & HASH_FFACTOR)
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hctl->ffactor = info->ffactor;
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/*
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* SHM hash tables have fixed directory size passed by the caller.
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@ -603,8 +599,6 @@ hdefault(HTAB *hashp)
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hctl->num_partitions = 0; /* not partitioned */
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hctl->ffactor = DEF_FFACTOR;
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/* table has no fixed maximum size */
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hctl->max_dsize = NO_MAX_DSIZE;
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@ -670,11 +664,10 @@ init_htab(HTAB *hashp, long nelem)
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SpinLockInit(&(hctl->freeList[i].mutex));
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/*
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* Divide number of elements by the fill factor to determine a desired
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* number of buckets. Allocate space for the next greater power of two
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* number of buckets
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* Allocate space for the next greater power of two number of buckets,
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* assuming a desired maximum load factor of 1.
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*/
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nbuckets = next_pow2_int((nelem - 1) / hctl->ffactor + 1);
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nbuckets = next_pow2_int(nelem);
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/*
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* In a partitioned table, nbuckets must be at least equal to
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@ -733,7 +726,6 @@ init_htab(HTAB *hashp, long nelem)
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"DIRECTORY SIZE ", hctl->dsize,
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"SEGMENT SIZE ", hctl->ssize,
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"SEGMENT SHIFT ", hctl->sshift,
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"FILL FACTOR ", hctl->ffactor,
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"MAX BUCKET ", hctl->max_bucket,
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"HIGH MASK ", hctl->high_mask,
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"LOW MASK ", hctl->low_mask,
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@ -761,7 +753,7 @@ hash_estimate_size(long num_entries, Size entrysize)
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elementAllocCnt;
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/* estimate number of buckets wanted */
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nBuckets = next_pow2_long((num_entries - 1) / DEF_FFACTOR + 1);
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nBuckets = next_pow2_long(num_entries);
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/* # of segments needed for nBuckets */
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nSegments = next_pow2_long((nBuckets - 1) / DEF_SEGSIZE + 1);
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/* directory entries */
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@ -804,7 +796,7 @@ hash_select_dirsize(long num_entries)
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nDirEntries;
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/* estimate number of buckets wanted */
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nBuckets = next_pow2_long((num_entries - 1) / DEF_FFACTOR + 1);
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nBuckets = next_pow2_long(num_entries);
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/* # of segments needed for nBuckets */
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nSegments = next_pow2_long((nBuckets - 1) / DEF_SEGSIZE + 1);
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/* directory entries */
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@ -975,7 +967,7 @@ hash_search_with_hash_value(HTAB *hashp,
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* order of these tests is to try to check cheaper conditions first.
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*/
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if (!IS_PARTITIONED(hctl) && !hashp->frozen &&
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hctl->freeList[0].nentries / (long) (hctl->max_bucket + 1) >= hctl->ffactor &&
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hctl->freeList[0].nentries > (long) (hctl->max_bucket + 1) &&
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!has_seq_scans(hashp))
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(void) expand_table(hashp);
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}
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@ -68,7 +68,6 @@ typedef struct HASHCTL
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long ssize; /* segment size */
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long dsize; /* (initial) directory size */
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long max_dsize; /* limit to dsize if dir size is limited */
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long ffactor; /* fill factor */
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Size keysize; /* hash key length in bytes */
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Size entrysize; /* total user element size in bytes */
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HashValueFunc hash; /* hash function */
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@ -83,7 +82,6 @@ typedef struct HASHCTL
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#define HASH_PARTITION 0x0001 /* Hashtable is used w/partitioned locking */
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#define HASH_SEGMENT 0x0002 /* Set segment size */
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#define HASH_DIRSIZE 0x0004 /* Set directory size (initial and max) */
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#define HASH_FFACTOR 0x0008 /* Set fill factor */
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#define HASH_ELEM 0x0010 /* Set keysize and entrysize */
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#define HASH_BLOBS 0x0020 /* Select support functions for binary keys */
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#define HASH_FUNCTION 0x0040 /* Set user defined hash function */
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