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Refactor initial hash lookup in dynahash.c 

The same pattern is used three times in dynahash.c to retrieve a bucket
number and a hash bucket from a hash value.  This has popped up while
discussing improvements for the type cache, where this piece of
refactoring would become useful.

Note that hash_search_with_hash_value() does not need the bucket number,
just the hash bucket.

Author: Teodor Sigaev
Reviewed-by: Aleksander Alekseev, Michael Paquier
Discussion: https://postgr.es/m/5812a6e5-68ae-4d84-9d85-b443176966a1@sigaev.ru
This commit is contained in:
Michael Paquier 2024-03-15 07:57:17 +09:00
parent 4169850f0b
commit cc5ef90edd
1 changed files with 33 additions and 42 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

75
src/backend/utils/hash/dynahash.c
View File

@ -273,6 +273,8 @@ static void hdefault(HTAB *hashp);
static int choose_nelem_alloc(Size entrysize);
static bool init_htab(HTAB *hashp, long nelem);
static void hash_corrupted(HTAB *hashp);
static uint32 hash_initial_lookup(HTAB *hashp, uint32 hashvalue,
HASHBUCKET **bucketptr);
static long next_pow2_long(long num);
static int next_pow2_int(long num);
static void register_seq_scan(HTAB *hashp);
@ -972,10 +974,6 @@ hash_search_with_hash_value(HTAB *hashp,
HASHHDR *hctl = hashp->hctl;
int freelist_idx = FREELIST_IDX(hctl, hashvalue);
Size keysize;
uint32 bucket;
long segment_num;
long segment_ndx;
HASHSEGMENT segp;
HASHBUCKET currBucket;
HASHBUCKET *prevBucketPtr;
HashCompareFunc match;
@ -1008,17 +1006,7 @@ hash_search_with_hash_value(HTAB *hashp,
/*
* Do the initial lookup
*/
bucket = calc_bucket(hctl, hashvalue);
segment_num = bucket >> hashp->sshift;
segment_ndx = MOD(bucket, hashp->ssize);
segp = hashp->dir[segment_num];
if (segp == NULL)
hash_corrupted(hashp);
prevBucketPtr = &segp[segment_ndx];
(void) hash_initial_lookup(hashp, hashvalue, &prevBucketPtr);
currBucket = *prevBucketPtr;
/*
@ -1159,14 +1147,10 @@ hash_update_hash_key(HTAB *hashp,
const void *newKeyPtr)
{
HASHELEMENT *existingElement = ELEMENT_FROM_KEY(existingEntry);
HASHHDR *hctl = hashp->hctl;
uint32 newhashvalue;
Size keysize;
uint32 bucket;
uint32 newbucket;
long segment_num;
long segment_ndx;
HASHSEGMENT segp;
HASHBUCKET currBucket;
HASHBUCKET *prevBucketPtr;
HASHBUCKET *oldPrevPtr;
@ -1187,17 +1171,8 @@ hash_update_hash_key(HTAB *hashp,
* this to be able to unlink it from its hash chain, but as a side benefit
* we can verify the validity of the passed existingEntry pointer.
*/
bucket = calc_bucket(hctl, existingElement->hashvalue);
segment_num = bucket >> hashp->sshift;
segment_ndx = MOD(bucket, hashp->ssize);
segp = hashp->dir[segment_num];
if (segp == NULL)
hash_corrupted(hashp);
prevBucketPtr = &segp[segment_ndx];
bucket = hash_initial_lookup(hashp, existingElement->hashvalue,
&prevBucketPtr);
currBucket = *prevBucketPtr;
while (currBucket != NULL)
@ -1219,18 +1194,7 @@ hash_update_hash_key(HTAB *hashp,
* chain we want to put the entry into.
*/
newhashvalue = hashp->hash(newKeyPtr, hashp->keysize);
newbucket = calc_bucket(hctl, newhashvalue);
segment_num = newbucket >> hashp->sshift;
segment_ndx = MOD(newbucket, hashp->ssize);
segp = hashp->dir[segment_num];
if (segp == NULL)
hash_corrupted(hashp);
prevBucketPtr = &segp[segment_ndx];
newbucket = hash_initial_lookup(hashp, newhashvalue, &prevBucketPtr);
currBucket = *prevBucketPtr;
/*
@ -1741,6 +1705,33 @@ element_alloc(HTAB *hashp, int nelem, int freelist_idx)
return true;
}
/*
* Do initial lookup of a bucket for the given hash value, retrieving its
* bucket number and its hash bucket.
*/
static inline uint32
hash_initial_lookup(HTAB *hashp, uint32 hashvalue, HASHBUCKET **bucketptr)
{
HASHHDR *hctl = hashp->hctl;
HASHSEGMENT segp;
long segment_num;
long segment_ndx;
uint32 bucket;
bucket = calc_bucket(hctl, hashvalue);
segment_num = bucket >> hashp->sshift;
segment_ndx = MOD(bucket, hashp->ssize);
segp = hashp->dir[segment_num];
if (segp == NULL)
hash_corrupted(hashp);
*bucketptr = &segp[segment_ndx];
return bucket;
}
/* complain when we have detected a corrupted hashtable */
static void
hash_corrupted(HTAB *hashp)