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hashsort.c
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1 /*-------------------------------------------------------------------------
2  *
3  * hashsort.c
4  * Sort tuples for insertion into a new hash index.
5  *
6  * When building a very large hash index, we pre-sort the tuples by bucket
7  * number to improve locality of access to the index, and thereby avoid
8  * thrashing. We use tuplesort.c to sort the given index tuples into order.
9  *
10  * Note: if the number of rows in the table has been underestimated,
11  * bucket splits may occur during the index build. In that case we'd
12  * be inserting into two or more buckets for each possible masked-off
13  * hash code value. That's no big problem though, since we'll still have
14  * plenty of locality of access.
15  *
16  *
17  * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
18  * Portions Copyright (c) 1994, Regents of the University of California
19  *
20  * IDENTIFICATION
21  * src/backend/access/hash/hashsort.c
22  *
23  *-------------------------------------------------------------------------
24  */
25 
26 #include "postgres.h"
27 
28 #include "access/hash.h"
29 #include "miscadmin.h"
30 #include "utils/tuplesort.h"
31 
32 
33 /*
34  * Status record for spooling/sorting phase.
35  */
36 struct HSpool
37 {
38  Tuplesortstate *sortstate; /* state data for tuplesort.c */
40 
41  /*
42  * We sort the hash keys based on the buckets they belong to. Below masks
43  * are used in _hash_hashkey2bucket to determine the bucket of given hash
44  * key.
45  */
49 };
50 
51 
52 /*
53  * create and initialize a spool structure
54  */
55 HSpool *
57 {
58  HSpool *hspool = (HSpool *) palloc0(sizeof(HSpool));
59 
60  hspool->index = index;
61 
62  /*
63  * Determine the bitmask for hash code values. Since there are currently
64  * num_buckets buckets in the index, the appropriate mask can be computed
65  * as follows.
66  *
67  * NOTE : This hash mask calculation should be in sync with similar
68  * calculation in _hash_init_metabuffer.
69  */
70  hspool->high_mask = (((uint32) 1) << _hash_log2(num_buckets + 1)) - 1;
71  hspool->low_mask = (hspool->high_mask >> 1);
72  hspool->max_buckets = num_buckets - 1;
73 
74  /*
75  * We size the sort area as maintenance_work_mem rather than work_mem to
76  * speed index creation. This should be OK since a single backend can't
77  * run multiple index creations in parallel.
78  */
80  index,
81  hspool->high_mask,
82  hspool->low_mask,
83  hspool->max_buckets,
85  false);
86 
87  return hspool;
88 }
89 
90 /*
91  * clean up a spool structure and its substructures.
92  */
93 void
95 {
96  tuplesort_end(hspool->sortstate);
97  pfree(hspool);
98 }
99 
100 /*
101  * spool an index entry into the sort file.
102  */
103 void
104 _h_spool(HSpool *hspool, ItemPointer self, Datum *values, bool *isnull)
105 {
107  self, values, isnull);
108 }
109 
110 /*
111  * given a spool loaded by successive calls to _h_spool,
112  * create an entire index.
113  */
114 void
115 _h_indexbuild(HSpool *hspool, Relation heapRel)
116 {
117  IndexTuple itup;
118 #ifdef USE_ASSERT_CHECKING
119  uint32 hashkey = 0;
120 #endif
121 
123 
124  while ((itup = tuplesort_getindextuple(hspool->sortstate, true)) != NULL)
125  {
126  /*
127  * Technically, it isn't critical that hash keys be found in sorted
128  * order, since this sorting is only used to increase locality of
129  * access as a performance optimization. It still seems like a good
130  * idea to test tuplesort.c's handling of hash index tuple sorts
131  * through an assertion, though.
132  */
133 #ifdef USE_ASSERT_CHECKING
134  uint32 lasthashkey = hashkey;
135 
137  hspool->max_buckets, hspool->high_mask,
138  hspool->low_mask);
139  Assert(hashkey >= lasthashkey);
140 #endif
141 
142  _hash_doinsert(hspool->index, itup, heapRel);
143  }
144 }
IndexTuple tuplesort_getindextuple(Tuplesortstate *state, bool forward)
Definition: tuplesort.c:2053
void _hash_doinsert(Relation rel, IndexTuple itup, Relation heapRel)
Definition: hashinsert.c:36
void tuplesort_performsort(Tuplesortstate *state)
Definition: tuplesort.c:1656
Bucket _hash_hashkey2bucket(uint32 hashkey, uint32 maxbucket, uint32 highmask, uint32 lowmask)
Definition: hashutil.c:125
Tuplesortstate * sortstate
Definition: hashsort.c:38
uint32 low_mask
Definition: hashsort.c:47
Definition: type.h:89
uint32 high_mask
Definition: hashsort.c:46
void pfree(void *pointer)
Definition: mcxt.c:949
uint32 _hash_get_indextuple_hashkey(IndexTuple itup)
Definition: hashutil.c:299
Tuplesortstate * tuplesort_begin_index_hash(Relation heapRel, Relation indexRel, uint32 high_mask, uint32 low_mask, uint32 max_buckets, int workMem, bool randomAccess)
Definition: tuplesort.c:932
void _h_spool(HSpool *hspool, ItemPointer self, Datum *values, bool *isnull)
Definition: hashsort.c:104
void _h_indexbuild(HSpool *hspool, Relation heapRel)
Definition: hashsort.c:115
unsigned int uint32
Definition: c.h:258
void * palloc0(Size size)
Definition: mcxt.c:877
uintptr_t Datum
Definition: postgres.h:372
uint32 max_buckets
Definition: hashsort.c:48
Relation index
Definition: hashsort.c:39
void tuplesort_putindextuplevalues(Tuplesortstate *state, Relation rel, ItemPointer self, Datum *values, bool *isnull)
Definition: tuplesort.c:1344
int maintenance_work_mem
Definition: globals.c:114
#define Assert(condition)
Definition: c.h:681
static Datum values[MAXATTR]
Definition: bootstrap.c:164
void _h_spooldestroy(HSpool *hspool)
Definition: hashsort.c:94
uint32 _hash_log2(uint32 num)
Definition: hashutil.c:141
HSpool * _h_spoolinit(Relation heap, Relation index, uint32 num_buckets)
Definition: hashsort.c:56
void tuplesort_end(Tuplesortstate *state)
Definition: tuplesort.c:1104