02-hash_seq_init_with_hash_value.v5.patch

diff --git a/src/backend/utils/hash/dynahash.c b/src/backend/utils/hash/dynahash.c
index a4152080b5d..dfea7a904e2 100644
--- a/src/backend/utils/hash/dynahash.c
+++ b/src/backend/utils/hash/dynahash.c
@@ -962,6 +962,33 @@ hash_search(HTAB *hashp,
 									   foundPtr);
 }
 
+/*
+ * Do initial lookup of a bucket by the given hash value.
+ */
+static inline HASHBUCKET*
+hash_initial_lookup(HTAB *hashp, uint32 hashvalue, uint32 *bucket)
+{
+	HASHHDR    *hctl = hashp->hctl;
+	HASHSEGMENT segp;
+	long		segment_num;
+	long		segment_ndx;
+
+	/*
+	 * 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);
+
+	return &segp[segment_ndx];
+}
+
 void *
 hash_search_with_hash_value(HTAB *hashp,
 							const void *keyPtr,
@@ -973,9 +1000,6 @@ hash_search_with_hash_value(HTAB *hashp,
 	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 +1032,7 @@ 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];
+	prevBucketPtr = hash_initial_lookup(hashp, hashvalue, &bucket);
 	currBucket = *prevBucketPtr;
 
 	/*
@@ -1159,14 +1173,10 @@ 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 +1197,7 @@ 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];
+	prevBucketPtr = hash_initial_lookup(hashp, existingElement->hashvalue, &bucket);
 	currBucket = *prevBucketPtr;
 
 	while (currBucket != NULL)
@@ -1219,18 +1219,7 @@ 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];
+	prevBucketPtr = hash_initial_lookup(hashp, newhashvalue, &newbucket);
 	currBucket = *prevBucketPtr;
 
 	/*
@@ -1423,10 +1412,27 @@ hash_seq_init(HASH_SEQ_STATUS *status, HTAB *hashp)
 	status->hashp = hashp;
 	status->curBucket = 0;
 	status->curEntry = NULL;
+	status->hasHashvalue = false;
 	if (!hashp->frozen)
 		register_seq_scan(hashp);
 }
 
+/*
+ * Same as above but scan by the given hash value.
+ * See also hash_seq_search().
+ */
+void
+hash_seq_init_with_hash_value(HASH_SEQ_STATUS *status, HTAB *hashp,
+							  uint32 hashvalue)
+{
+	hash_seq_init(status, hashp);
+
+	status->hasHashvalue = true;
+	status->hashvalue = hashvalue;
+
+	status->curEntry = *hash_initial_lookup(hashp, hashvalue, &status->curBucket);
+}
+
 void *
 hash_seq_search(HASH_SEQ_STATUS *status)
 {
@@ -1440,6 +1446,24 @@ hash_seq_search(HASH_SEQ_STATUS *status)
 	uint32		curBucket;
 	HASHELEMENT *curElem;
 
+	if (status->hasHashvalue)
+	{
+		/*
+		 * Scan entries only in the current bucket because only this bucket can
+		 * contain entries with the given hash value.
+		 */
+		while ((curElem = status->curEntry) != NULL)
+		{
+			status->curEntry = curElem->link;
+			if (status->hashvalue != curElem->hashvalue)
+				continue;
+			return (void *) ELEMENTKEY(curElem);
+		}
+
+		hash_seq_term(status);
+		return NULL;
+	}
+
 	if ((curElem = status->curEntry) != NULL)
 	{
 		/* Continuing scan of curBucket... */
diff --git a/src/include/utils/hsearch.h b/src/include/utils/hsearch.h
index da26941f6db..c99d74625f7 100644
--- a/src/include/utils/hsearch.h
+++ b/src/include/utils/hsearch.h
@@ -122,6 +122,8 @@ typedef struct
 	HTAB	   *hashp;
 	uint32		curBucket;		/* index of current bucket */
 	HASHELEMENT *curEntry;		/* current entry in bucket */
+	bool		hasHashvalue;	/* true if hashvalue was provided */
+	uint32		hashvalue;		/* hashvalue to start seqscan over hash */
 } HASH_SEQ_STATUS;
 
 /*
@@ -141,6 +143,8 @@ extern bool hash_update_hash_key(HTAB *hashp, void *existingEntry,
 								 const void *newKeyPtr);
 extern long hash_get_num_entries(HTAB *hashp);
 extern void hash_seq_init(HASH_SEQ_STATUS *status, HTAB *hashp);
+extern void hash_seq_init_with_hash_value(HASH_SEQ_STATUS *status, HTAB *hashp,
+										  uint32 hashvalue);
 extern void *hash_seq_search(HASH_SEQ_STATUS *status);
 extern void hash_seq_term(HASH_SEQ_STATUS *status);
 extern void hash_freeze(HTAB *hashp);