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) 1996-2021, 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 "commands/progress.h"
30 #include "miscadmin.h"
31 #include "pgstat.h"
32 #include "port/pg_bitutils.h"
33 #include "utils/tuplesort.h"
34
35
36 /*
37 * Status record for spooling/sorting phase.
38 */
39 struct HSpool
40 {
41 Tuplesortstate *sortstate; /* state data for tuplesort.c */
42 Relation index;
43
44 /*
45 * We sort the hash keys based on the buckets they belong to. Below masks
46 * are used in _hash_hashkey2bucket to determine the bucket of given hash
47 * key.
48 */
49 uint32 high_mask;
50 uint32 low_mask;
51 uint32 max_buckets;
52 };
53
54
55 /*
56 * create and initialize a spool structure
57 */
58 HSpool *
_h_spoolinit(Relation heap,Relation index,uint32 num_buckets)59 _h_spoolinit(Relation heap, Relation index, uint32 num_buckets)
60 {
61 HSpool *hspool = (HSpool *) palloc0(sizeof(HSpool));
62
63 hspool->index = index;
64
65 /*
66 * Determine the bitmask for hash code values. Since there are currently
67 * num_buckets buckets in the index, the appropriate mask can be computed
68 * as follows.
69 *
70 * NOTE : This hash mask calculation should be in sync with similar
71 * calculation in _hash_init_metabuffer.
72 */
73 hspool->high_mask = pg_nextpower2_32(num_buckets + 1) - 1;
74 hspool->low_mask = (hspool->high_mask >> 1);
75 hspool->max_buckets = num_buckets - 1;
76
77 /*
78 * We size the sort area as maintenance_work_mem rather than work_mem to
79 * speed index creation. This should be OK since a single backend can't
80 * run multiple index creations in parallel.
81 */
82 hspool->sortstate = tuplesort_begin_index_hash(heap,
83 index,
84 hspool->high_mask,
85 hspool->low_mask,
86 hspool->max_buckets,
87 maintenance_work_mem,
88 NULL,
89 false);
90
91 return hspool;
92 }
93
94 /*
95 * clean up a spool structure and its substructures.
96 */
97 void
_h_spooldestroy(HSpool * hspool)98 _h_spooldestroy(HSpool *hspool)
99 {
100 tuplesort_end(hspool->sortstate);
101 pfree(hspool);
102 }
103
104 /*
105 * spool an index entry into the sort file.
106 */
107 void
_h_spool(HSpool * hspool,ItemPointer self,Datum * values,bool * isnull)108 _h_spool(HSpool *hspool, ItemPointer self, Datum *values, bool *isnull)
109 {
110 tuplesort_putindextuplevalues(hspool->sortstate, hspool->index,
111 self, values, isnull);
112 }
113
114 /*
115 * given a spool loaded by successive calls to _h_spool,
116 * create an entire index.
117 */
118 void
_h_indexbuild(HSpool * hspool,Relation heapRel)119 _h_indexbuild(HSpool *hspool, Relation heapRel)
120 {
121 IndexTuple itup;
122 int64 tups_done = 0;
123 #ifdef USE_ASSERT_CHECKING
124 uint32 hashkey = 0;
125 #endif
126
127 tuplesort_performsort(hspool->sortstate);
128
129 while ((itup = tuplesort_getindextuple(hspool->sortstate, true)) != NULL)
130 {
131 /*
132 * Technically, it isn't critical that hash keys be found in sorted
133 * order, since this sorting is only used to increase locality of
134 * access as a performance optimization. It still seems like a good
135 * idea to test tuplesort.c's handling of hash index tuple sorts
136 * through an assertion, though.
137 */
138 #ifdef USE_ASSERT_CHECKING
139 uint32 lasthashkey = hashkey;
140
141 hashkey = _hash_hashkey2bucket(_hash_get_indextuple_hashkey(itup),
142 hspool->max_buckets, hspool->high_mask,
143 hspool->low_mask);
144 Assert(hashkey >= lasthashkey);
145 #endif
146
147 _hash_doinsert(hspool->index, itup, heapRel);
148
149 pgstat_progress_update_param(PROGRESS_CREATEIDX_TUPLES_DONE,
150 ++tups_done);
151 }
152 }
153