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Commitd0f0200

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Introduce hash_search_with_hash_value() function
This new function iterates hash entries with given hash values. This functionis designed to avoid full sequential hash search in the syscache invalidationcallbacks.Discussion:https://postgr.es/m/5812a6e5-68ae-4d84-9d85-b443176966a1%40sigaev.ruAuthor: Teodor SigaevReviewed-by: Aleksander Alekseev, Tom Lane, Michael Paquier, Roman ZharkovReviewed-by: Andrei Lepikhov
1 parent3ab2668 commitd0f0200

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2 files changed

+43
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2 files changed

+43
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‎src/backend/utils/hash/dynahash.c

Lines changed: 38 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1387,10 +1387,30 @@ hash_seq_init(HASH_SEQ_STATUS *status, HTAB *hashp)
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status->hashp=hashp;
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status->curBucket=0;
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status->curEntry=NULL;
1390+
status->hasHashvalue= false;
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if (!hashp->frozen)
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register_seq_scan(hashp);
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}
13931394

1395+
/*
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* Same as above but scan by the given hash value.
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* See also hash_seq_search().
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*/
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void
1400+
hash_seq_init_with_hash_value(HASH_SEQ_STATUS*status,HTAB*hashp,
1401+
uint32hashvalue)
1402+
{
1403+
HASHBUCKET*bucketPtr;
1404+
1405+
hash_seq_init(status,hashp);
1406+
1407+
status->hasHashvalue= true;
1408+
status->hashvalue=hashvalue;
1409+
1410+
status->curBucket=hash_initial_lookup(hashp,hashvalue,&bucketPtr);
1411+
status->curEntry=*bucketPtr;
1412+
}
1413+
13941414
void*
13951415
hash_seq_search(HASH_SEQ_STATUS*status)
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{
@@ -1404,6 +1424,24 @@ hash_seq_search(HASH_SEQ_STATUS *status)
14041424
uint32curBucket;
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HASHELEMENT*curElem;
14061426

1427+
if (status->hasHashvalue)
1428+
{
1429+
/*
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* Scan entries only in the current bucket because only this bucket
1431+
* can contain entries with the given hash value.
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*/
1433+
while ((curElem=status->curEntry)!=NULL)
1434+
{
1435+
status->curEntry=curElem->link;
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if (status->hashvalue!=curElem->hashvalue)
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continue;
1438+
return (void*)ELEMENTKEY(curElem);
1439+
}
1440+
1441+
hash_seq_term(status);
1442+
returnNULL;
1443+
}
1444+
14071445
if ((curElem=status->curEntry)!=NULL)
14081446
{
14091447
/* Continuing scan of curBucket... */

‎src/include/utils/hsearch.h

Lines changed: 5 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -122,6 +122,8 @@ typedef struct
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HTAB*hashp;
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uint32curBucket;/* index of current bucket */
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HASHELEMENT*curEntry;/* current entry in bucket */
125+
boolhasHashvalue;/* true if hashvalue was provided */
126+
uint32hashvalue;/* hashvalue to start seqscan over hash */
125127
}HASH_SEQ_STATUS;
126128

127129
/*
@@ -141,6 +143,9 @@ extern bool hash_update_hash_key(HTAB *hashp, void *existingEntry,
141143
constvoid*newKeyPtr);
142144
externlonghash_get_num_entries(HTAB*hashp);
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externvoidhash_seq_init(HASH_SEQ_STATUS*status,HTAB*hashp);
146+
externvoidhash_seq_init_with_hash_value(HASH_SEQ_STATUS*status,
147+
HTAB*hashp,
148+
uint32hashvalue);
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externvoid*hash_seq_search(HASH_SEQ_STATUS*status);
145150
externvoidhash_seq_term(HASH_SEQ_STATUS*status);
146151
externvoidhash_freeze(HTAB*hashp);

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