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Commit8cf739d

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Fix building of large (bigger than shared_buffers) hash indexes.
When the index is predicted to need more than NBuffers buckets,CREATE INDEX attempts to sort the index entries by hash key beforeinsertion, so as to reduce thrashing. This code path got broken bycommit9f03ca9, which overlooked that _hash_form_tuple() is notjust an alias for index_form_tuple(). The index got built anyway, butwith garbage data, so that searches for pre-existing tuples alwaysfailed. Fix by refactoring to separate construction of the indexabledata from calling index_form_tuple().Per bug #14210 from Daniel Newman. Back-patch to 9.5 where thebug was introduced.Report: <20160623162507.17237.39471@wrigleys.postgresql.org>
1 parent9e9c38e commit8cf739d

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3 files changed

+48
-35
lines changed

3 files changed

+48
-35
lines changed

‎src/backend/access/hash/hash.c

Lines changed: 18 additions & 16 deletions
Original file line numberDiff line numberDiff line change
@@ -176,19 +176,25 @@ hashbuildCallback(Relation index,
176176
void*state)
177177
{
178178
HashBuildState*buildstate= (HashBuildState*)state;
179+
Datumindex_values[1];
180+
boolindex_isnull[1];
179181
IndexTupleitup;
180182

181-
/* Hash indexes don't index nulls, see notes in hashinsert */
182-
if (isnull[0])
183+
/* convert data to a hash key; on failure, do not insert anything */
184+
if (!_hash_convert_tuple(index,
185+
values,isnull,
186+
index_values,index_isnull))
183187
return;
184188

185189
/* Either spool the tuple for sorting, or just put it into the index */
186190
if (buildstate->spool)
187-
_h_spool(buildstate->spool,&htup->t_self,values,isnull);
191+
_h_spool(buildstate->spool,&htup->t_self,
192+
index_values,index_isnull);
188193
else
189194
{
190195
/* form an index tuple and point it at the heap tuple */
191-
itup=_hash_form_tuple(index,values,isnull);
196+
itup=index_form_tuple(RelationGetDescr(index),
197+
index_values,index_isnull);
192198
itup->t_tid=htup->t_self;
193199
_hash_doinsert(index,itup);
194200
pfree(itup);
@@ -208,22 +214,18 @@ hashinsert(Relation rel, Datum *values, bool *isnull,
208214
ItemPointerht_ctid,RelationheapRel,
209215
IndexUniqueCheckcheckUnique)
210216
{
217+
Datumindex_values[1];
218+
boolindex_isnull[1];
211219
IndexTupleitup;
212220

213-
/*
214-
* If the single index key is null, we don't insert it into the index.
215-
* Hash tables support scans on '='. Relational algebra says that A = B
216-
* returns null if either A or B is null. This means that no
217-
* qualification used in an index scan could ever return true on a null
218-
* attribute. It also means that indices can't be used by ISNULL or
219-
* NOTNULL scans, but that's an artifact of the strategy map architecture
220-
* chosen in 1986, not of the way nulls are handled here.
221-
*/
222-
if (isnull[0])
221+
/* convert data to a hash key; on failure, do not insert anything */
222+
if (!_hash_convert_tuple(rel,
223+
values,isnull,
224+
index_values,index_isnull))
223225
return false;
224226

225-
/*generate an index tuple */
226-
itup=_hash_form_tuple(rel,values,isnull);
227+
/*form an index tuple and point it at the heap tuple */
228+
itup=index_form_tuple(RelationGetDescr(rel),index_values,index_isnull);
227229
itup->t_tid=*ht_ctid;
228230

229231
_hash_doinsert(rel,itup);

‎src/backend/access/hash/hashutil.c

Lines changed: 27 additions & 17 deletions
Original file line numberDiff line numberDiff line change
@@ -240,27 +240,37 @@ _hash_get_indextuple_hashkey(IndexTuple itup)
240240
}
241241

242242
/*
243-
* _hash_form_tuple - form an index tuple containing hash code only
243+
* _hash_convert_tuple - convert raw index data to hash key
244+
*
245+
* Inputs: values and isnull arrays for the user data column(s)
246+
* Outputs: values and isnull arrays for the index tuple, suitable for
247+
*passing to index_form_tuple().
248+
*
249+
* Returns true if successful, false if not (because there are null values).
250+
* On a false result, the given data need not be indexed.
251+
*
252+
* Note: callers know that the index-column arrays are always of length 1.
253+
* In principle, there could be more than one input column, though we do not
254+
* currently support that.
244255
*/
245-
IndexTuple
246-
_hash_form_tuple(Relationindex,Datum*values,bool*isnull)
256+
bool
257+
_hash_convert_tuple(Relationindex,
258+
Datum*user_values,bool*user_isnull,
259+
Datum*index_values,bool*index_isnull)
247260
{
248-
IndexTupleitup;
249261
uint32hashkey;
250-
Datumhashkeydatum;
251-
TupleDeschashdesc;
252262

253-
if (isnull[0])
254-
hashkeydatum= (Datum)0;
255-
else
256-
{
257-
hashkey=_hash_datum2hashkey(index,values[0]);
258-
hashkeydatum=UInt32GetDatum(hashkey);
259-
}
260-
hashdesc=RelationGetDescr(index);
261-
Assert(hashdesc->natts==1);
262-
itup=index_form_tuple(hashdesc,&hashkeydatum,isnull);
263-
returnitup;
263+
/*
264+
* We do not insert null values into hash indexes. This is okay because
265+
* the only supported search operator is '=', and we assume it is strict.
266+
*/
267+
if (user_isnull[0])
268+
return false;
269+
270+
hashkey=_hash_datum2hashkey(index,user_values[0]);
271+
index_values[0]=UInt32GetDatum(hashkey);
272+
index_isnull[0]=false;
273+
returntrue;
264274
}
265275

266276
/*

‎src/include/access/hash.h

Lines changed: 3 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -359,8 +359,9 @@ extern Bucket _hash_hashkey2bucket(uint32 hashkey, uint32 maxbucket,
359359
externuint32_hash_log2(uint32num);
360360
externvoid_hash_checkpage(Relationrel,Bufferbuf,intflags);
361361
externuint32_hash_get_indextuple_hashkey(IndexTupleitup);
362-
externIndexTuple_hash_form_tuple(Relationindex,
363-
Datum*values,bool*isnull);
362+
externbool_hash_convert_tuple(Relationindex,
363+
Datum*user_values,bool*user_isnull,
364+
Datum*index_values,bool*index_isnull);
364365
externOffsetNumber_hash_binsearch(Pagepage,uint32hash_value);
365366
externOffsetNumber_hash_binsearch_last(Pagepage,uint32hash_value);
366367

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