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Commit35ea756

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Refactor typcache.c's record typmod hash table.
Previously, tuple descriptors were stored in chains keyed by a fixed sizearray of OIDs. That meant there were effectively two levels of collisionchain -- one inside and one outside the hash table. Instead, let dynahash.clook after conflicts for us by supplying a proper hash and equal functionpair.This is a nice cleanup on its own, but also simplifies followupchanges allowing blessed TupleDescs to be shared between backendsparticipating in parallel query.Author: Thomas MunroReviewed-By: Andres FreundDiscussion:https://postgr.es/m/CAEepm%3D34GVhOL%2BarUx56yx7OPk7%3DqpGsv3CpO54feqjAwQKm5g%40mail.gmail.com
1 parent0052a02 commit35ea756

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3 files changed

+65
-38
lines changed

3 files changed

+65
-38
lines changed

‎src/backend/access/common/tupdesc.c

Lines changed: 27 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -19,13 +19,15 @@
1919

2020
#include"postgres.h"
2121

22+
#include"access/hash.h"
2223
#include"access/htup_details.h"
2324
#include"catalog/pg_collation.h"
2425
#include"catalog/pg_type.h"
2526
#include"miscadmin.h"
2627
#include"parser/parse_type.h"
2728
#include"utils/acl.h"
2829
#include"utils/builtins.h"
30+
#include"utils/hashutils.h"
2931
#include"utils/resowner_private.h"
3032
#include"utils/syscache.h"
3133

@@ -443,6 +445,31 @@ equalTupleDescs(TupleDesc tupdesc1, TupleDesc tupdesc2)
443445
return true;
444446
}
445447

448+
/*
449+
* hashTupleDesc
450+
*Compute a hash value for a tuple descriptor.
451+
*
452+
* If two tuple descriptors would be considered equal by equalTupleDescs()
453+
* then their hash value will be equal according to this function.
454+
*
455+
* Note that currently contents of constraint are not hashed - it'd be a bit
456+
* painful to do so, and conflicts just due to constraints are unlikely.
457+
*/
458+
uint32
459+
hashTupleDesc(TupleDescdesc)
460+
{
461+
uint32s;
462+
inti;
463+
464+
s=hash_combine(0,hash_uint32(desc->natts));
465+
s=hash_combine(s,hash_uint32(desc->tdtypeid));
466+
s=hash_combine(s,hash_uint32(desc->tdhasoid));
467+
for (i=0;i<desc->natts;++i)
468+
s=hash_combine(s,hash_uint32(TupleDescAttr(desc,i)->atttypid));
469+
470+
returns;
471+
}
472+
446473
/*
447474
* TupleDescInitEntry
448475
*This function initializes a single attribute structure in

‎src/backend/utils/cache/typcache.c

Lines changed: 36 additions & 38 deletions
Original file line numberDiff line numberDiff line change
@@ -133,19 +133,12 @@ typedef struct TypeCacheEnumData
133133
*
134134
* Stored record types are remembered in a linear array of TupleDescs,
135135
* which can be indexed quickly with the assigned typmod. There is also
136-
* a hash table to speed searches for matching TupleDescs. The hash key
137-
* uses just the first N columns' type OIDs, and so we may have multiple
138-
* entries with the same hash key.
136+
* a hash table to speed searches for matching TupleDescs.
139137
*/
140-
#defineREC_HASH_KEYS16/* use this many columns in hash key */
141138

142139
typedefstructRecordCacheEntry
143140
{
144-
/* the hash lookup key MUST BE FIRST */
145-
Oidhashkey[REC_HASH_KEYS];/* column type IDs, zero-filled */
146-
147-
/* list of TupleDescs for record types with this hashkey */
148-
List*tupdescs;
141+
TupleDesctupdesc;
149142
}RecordCacheEntry;
150143

151144
staticHTAB*RecordCacheHash=NULL;
@@ -1297,6 +1290,28 @@ lookup_rowtype_tupdesc_copy(Oid type_id, int32 typmod)
12971290
returnCreateTupleDescCopyConstr(tmp);
12981291
}
12991292

1293+
/*
1294+
* Hash function for the hash table of RecordCacheEntry.
1295+
*/
1296+
staticuint32
1297+
record_type_typmod_hash(constvoid*data,size_tsize)
1298+
{
1299+
RecordCacheEntry*entry= (RecordCacheEntry*)data;
1300+
1301+
returnhashTupleDesc(entry->tupdesc);
1302+
}
1303+
1304+
/*
1305+
* Match function for the hash table of RecordCacheEntry.
1306+
*/
1307+
staticint
1308+
record_type_typmod_compare(constvoid*a,constvoid*b,size_tsize)
1309+
{
1310+
RecordCacheEntry*left= (RecordCacheEntry*)a;
1311+
RecordCacheEntry*right= (RecordCacheEntry*)b;
1312+
1313+
returnequalTupleDescs(left->tupdesc,right->tupdesc) ?0 :1;
1314+
}
13001315

13011316
/*
13021317
* assign_record_type_typmod
@@ -1310,10 +1325,7 @@ assign_record_type_typmod(TupleDesc tupDesc)
13101325
{
13111326
RecordCacheEntry*recentry;
13121327
TupleDescentDesc;
1313-
Oidhashkey[REC_HASH_KEYS];
13141328
boolfound;
1315-
inti;
1316-
ListCell*l;
13171329
int32newtypmod;
13181330
MemoryContextoldcxt;
13191331

@@ -1325,45 +1337,31 @@ assign_record_type_typmod(TupleDesc tupDesc)
13251337
HASHCTLctl;
13261338

13271339
MemSet(&ctl,0,sizeof(ctl));
1328-
ctl.keysize=REC_HASH_KEYS*sizeof(Oid);
1340+
ctl.keysize=sizeof(TupleDesc);/* just the pointer */
13291341
ctl.entrysize=sizeof(RecordCacheEntry);
1342+
ctl.hash=record_type_typmod_hash;
1343+
ctl.match=record_type_typmod_compare;
13301344
RecordCacheHash=hash_create("Record information cache",64,
1331-
&ctl,HASH_ELEM |HASH_BLOBS);
1345+
&ctl,
1346+
HASH_ELEM |HASH_FUNCTION |HASH_COMPARE);
13321347

13331348
/* Also make sure CacheMemoryContext exists */
13341349
if (!CacheMemoryContext)
13351350
CreateCacheMemoryContext();
13361351
}
13371352

1338-
/* Find or create a hashtable entry for this hash class */
1339-
MemSet(hashkey,0,sizeof(hashkey));
1340-
for (i=0;i<tupDesc->natts;i++)
1341-
{
1342-
if (i >=REC_HASH_KEYS)
1343-
break;
1344-
hashkey[i]=TupleDescAttr(tupDesc,i)->atttypid;
1345-
}
1353+
/* Find or create a hashtable entry for this tuple descriptor */
13461354
recentry= (RecordCacheEntry*)hash_search(RecordCacheHash,
1347-
(void*)hashkey,
1355+
(void*)&tupDesc,
13481356
HASH_ENTER,&found);
1349-
if (!found)
1357+
if (found&&recentry->tupdesc!=NULL)
13501358
{
1351-
/* New entry ... hash_search initialized only the hash key */
1352-
recentry->tupdescs=NIL;
1353-
}
1354-
1355-
/* Look for existing record cache entry */
1356-
foreach(l,recentry->tupdescs)
1357-
{
1358-
entDesc= (TupleDesc)lfirst(l);
1359-
if (equalTupleDescs(tupDesc,entDesc))
1360-
{
1361-
tupDesc->tdtypmod=entDesc->tdtypmod;
1362-
return;
1363-
}
1359+
tupDesc->tdtypmod=recentry->tupdesc->tdtypmod;
1360+
return;
13641361
}
13651362

13661363
/* Not present, so need to manufacture an entry */
1364+
recentry->tupdesc=NULL;
13671365
oldcxt=MemoryContextSwitchTo(CacheMemoryContext);
13681366

13691367
if (RecordCacheArray==NULL)
@@ -1382,7 +1380,7 @@ assign_record_type_typmod(TupleDesc tupDesc)
13821380

13831381
/* if fail in subrs, no damage except possibly some wasted memory... */
13841382
entDesc=CreateTupleDescCopy(tupDesc);
1385-
recentry->tupdescs=lcons(entDesc,recentry->tupdescs);
1383+
recentry->tupdesc=entDesc;
13861384
/* mark it as a reference-counted tupdesc */
13871385
entDesc->tdrefcount=1;
13881386
/* now it's safe to advance NextRecordTypmod */

‎src/include/access/tupdesc.h

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -114,6 +114,8 @@ extern void DecrTupleDescRefCount(TupleDesc tupdesc);
114114

115115
externboolequalTupleDescs(TupleDesctupdesc1,TupleDesctupdesc2);
116116

117+
externuint32hashTupleDesc(TupleDesctupdesc);
118+
117119
externvoidTupleDescInitEntry(TupleDescdesc,
118120
AttrNumberattributeNumber,
119121
constchar*attributeName,

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