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Commit9563d5b

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Add regression test case exercising the sorting path for hash index build.
We've broken this code path at least twice in the past, so it's prudentto have a test case that covers it. To allow exercising the code pathwithout creating a very large (and slow to run) test case, redefine thesort threshold to be bounded by maintenance_work_mem as well as the numberof available buffers. While at it, fix an ancient oversight that whenbuilding a temp index, the number of available buffers is not NBuffers butNLocBuffer. Also, if assertions are enabled, apply a direct test that thesort actually does return the tuples in the expected order.Peter GeogheganPatch: <CAM3SWZTBAo4hjbBd780+MrOKiKp_TMo1N3A0Rw9_im8gbD7fQA@mail.gmail.com>
1 parent2781489 commit9563d5b

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4 files changed

+51
-6
lines changed

4 files changed

+51
-6
lines changed

‎src/backend/access/hash/hash.c‎

Lines changed: 17 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -22,6 +22,7 @@
2222
#include"access/relscan.h"
2323
#include"catalog/index.h"
2424
#include"commands/vacuum.h"
25+
#include"miscadmin.h"
2526
#include"optimizer/plancat.h"
2627
#include"utils/index_selfuncs.h"
2728
#include"utils/rel.h"
@@ -97,6 +98,7 @@ hashbuild(Relation heap, Relation index, IndexInfo *indexInfo)
9798
doublereltuples;
9899
doubleallvisfrac;
99100
uint32num_buckets;
101+
longsort_threshold;
100102
HashBuildStatebuildstate;
101103

102104
/*
@@ -120,12 +122,24 @@ hashbuild(Relation heap, Relation index, IndexInfo *indexInfo)
120122
* then we'll thrash horribly. To prevent that scenario, we can sort the
121123
* tuples by (expected) bucket number. However, such a sort is useless
122124
* overhead when the index does fit in RAM. We choose to sort if the
123-
* initial index size exceeds NBuffers.
125+
* initial index size exceeds maintenance_work_mem, or the number of
126+
* buffers usable for the index, whichever is less. (Limiting by the
127+
* number of buffers should reduce thrashing between PG buffers and kernel
128+
* buffers, which seems useful even if no physical I/O results. Limiting
129+
* by maintenance_work_mem is useful to allow easy testing of the sort
130+
* code path, and may be useful to DBAs as an additional control knob.)
124131
*
125132
* NOTE: this test will need adjustment if a bucket is ever different from
126-
* one page.
133+
* one page. Also, "initial index size" accounting does not include the
134+
* metapage, nor the first bitmap page.
127135
*/
128-
if (num_buckets >= (uint32)NBuffers)
136+
sort_threshold= (maintenance_work_mem*1024L) /BLCKSZ;
137+
if (index->rd_rel->relpersistence!=RELPERSISTENCE_TEMP)
138+
sort_threshold=Min(sort_threshold,NBuffers);
139+
else
140+
sort_threshold=Min(sort_threshold,NLocBuffer);
141+
142+
if (num_buckets >= (uint32)sort_threshold)
129143
buildstate.spool=_h_spoolinit(heap,index,num_buckets);
130144
else
131145
buildstate.spool=NULL;

‎src/backend/access/hash/hashsort.c‎

Lines changed: 20 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -37,6 +37,7 @@ struct HSpool
3737
{
3838
Tuplesortstate*sortstate;/* state data for tuplesort.c */
3939
Relationindex;
40+
uint32hash_mask;/* bitmask for hash codes */
4041
};
4142

4243

@@ -47,7 +48,6 @@ HSpool *
4748
_h_spoolinit(Relationheap,Relationindex,uint32num_buckets)
4849
{
4950
HSpool*hspool= (HSpool*)palloc0(sizeof(HSpool));
50-
uint32hash_mask;
5151

5252
hspool->index=index;
5353

@@ -60,7 +60,7 @@ _h_spoolinit(Relation heap, Relation index, uint32 num_buckets)
6060
* we could just compute num_buckets - 1. We prefer not to assume that
6161
* here, though.
6262
*/
63-
hash_mask= (((uint32)1) <<_hash_log2(num_buckets))-1;
63+
hspool->hash_mask= (((uint32)1) <<_hash_log2(num_buckets))-1;
6464

6565
/*
6666
* We size the sort area as maintenance_work_mem rather than work_mem to
@@ -69,7 +69,7 @@ _h_spoolinit(Relation heap, Relation index, uint32 num_buckets)
6969
*/
7070
hspool->sortstate=tuplesort_begin_index_hash(heap,
7171
index,
72-
hash_mask,
72+
hspool->hash_mask,
7373
maintenance_work_mem,
7474
false);
7575

@@ -105,12 +105,29 @@ _h_indexbuild(HSpool *hspool)
105105
{
106106
IndexTupleitup;
107107
boolshould_free;
108+
#ifdefUSE_ASSERT_CHECKING
109+
uint32hashkey=0;
110+
#endif
108111

109112
tuplesort_performsort(hspool->sortstate);
110113

111114
while ((itup=tuplesort_getindextuple(hspool->sortstate,
112115
true,&should_free))!=NULL)
113116
{
117+
/*
118+
* Technically, it isn't critical that hash keys be found in sorted
119+
* order, since this sorting is only used to increase locality of
120+
* access as a performance optimization. It still seems like a good
121+
* idea to test tuplesort.c's handling of hash index tuple sorts
122+
* through an assertion, though.
123+
*/
124+
#ifdefUSE_ASSERT_CHECKING
125+
uint32lasthashkey=hashkey;
126+
127+
hashkey=_hash_get_indextuple_hashkey(itup)&hspool->hash_mask;
128+
Assert(hashkey >=lasthashkey);
129+
#endif
130+
114131
_hash_doinsert(hspool->index,itup);
115132
if (should_free)
116133
pfree(itup);

‎src/test/regress/expected/create_index.out‎

Lines changed: 7 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2346,6 +2346,13 @@ CREATE UNLOGGED TABLE unlogged_hash_table (id int4);
23462346
CREATE INDEX unlogged_hash_index ON unlogged_hash_table USING hash (id int4_ops);
23472347
DROP TABLE unlogged_hash_table;
23482348
-- CREATE INDEX hash_ovfl_index ON hash_ovfl_heap USING hash (x int4_ops);
2349+
-- Test hash index build tuplesorting. Force hash tuplesort using low
2350+
-- maintenance_work_mem setting and fillfactor:
2351+
SET maintenance_work_mem = '1MB';
2352+
CREATE INDEX hash_tuplesort_idx ON tenk1 USING hash (stringu1 name_ops) WITH (fillfactor = 10);
2353+
WARNING: hash indexes are not WAL-logged and their use is discouraged
2354+
DROP INDEX hash_tuplesort_idx;
2355+
RESET maintenance_work_mem;
23492356
--
23502357
-- Test functional index
23512358
--

‎src/test/regress/sql/create_index.sql‎

Lines changed: 7 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -690,6 +690,13 @@ DROP TABLE unlogged_hash_table;
690690

691691
-- CREATE INDEX hash_ovfl_index ON hash_ovfl_heap USING hash (x int4_ops);
692692

693+
-- Test hash index build tuplesorting. Force hash tuplesort using low
694+
-- maintenance_work_mem setting and fillfactor:
695+
SET maintenance_work_mem='1MB';
696+
CREATEINDEXhash_tuplesort_idxON tenk1 USING hash (stringu1 name_ops) WITH (fillfactor=10);
697+
DROPINDEX hash_tuplesort_idx;
698+
RESET maintenance_work_mem;
699+
693700

694701
--
695702
-- Test functional index

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