1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
|
/*-------------------------------------------------------------------------
*
* hashscan.c
* manage scans on hash tables
*
* Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/access/hash/hashscan.c,v 1.29 2002/09/04 20:31:09 momjian Exp $
*
* NOTES
* Because we can be doing an index scan on a relation while we
* update it, we need to avoid missing data that moves around in
* the index. The routines and global variables in this file
* guarantee that all scans in the local address space stay
* correctly positioned. This is all we need to worry about, since
* write locking guarantees that no one else will be on the same
* page at the same time as we are.
*
* The scheme is to manage a list of active scans in the current
* backend. Whenever we add or remove records from an index, we
* check the list of active scans to see if any has been affected.
* A scan is affected only if it is on the same relation, and the
* same page, as the update.
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/hash.h"
typedef struct HashScanListData
{
IndexScanDesc hashsl_scan;
struct HashScanListData *hashsl_next;
} HashScanListData;
typedef HashScanListData *HashScanList;
static HashScanList HashScans = (HashScanList) NULL;
static void _hash_scandel(IndexScanDesc scan,
BlockNumber blkno, OffsetNumber offno);
/*
* AtEOXact_hash() --- clean up hash subsystem at xact abort or commit.
*
* This is here because it needs to touch this module's static var HashScans.
*/
void
AtEOXact_hash(void)
{
/*
* Note: these actions should only be necessary during xact abort; but
* they can't hurt during a commit.
*/
/*
* Reset the active-scans list to empty. We do not need to free the
* list elements, because they're all palloc()'d, so they'll go away
* at end of transaction anyway.
*/
HashScans = NULL;
/* If we were building a hash, we ain't anymore. */
BuildingHash = false;
}
/*
* _Hash_regscan() -- register a new scan.
*/
void
_hash_regscan(IndexScanDesc scan)
{
HashScanList new_el;
new_el = (HashScanList) palloc(sizeof(HashScanListData));
new_el->hashsl_scan = scan;
new_el->hashsl_next = HashScans;
HashScans = new_el;
}
/*
* _hash_dropscan() -- drop a scan from the scan list
*/
void
_hash_dropscan(IndexScanDesc scan)
{
HashScanList chk,
last;
last = (HashScanList) NULL;
for (chk = HashScans;
chk != (HashScanList) NULL && chk->hashsl_scan != scan;
chk = chk->hashsl_next)
last = chk;
if (chk == (HashScanList) NULL)
elog(ERROR, "hash scan list trashed; can't find 0x%p", (void *) scan);
if (last == (HashScanList) NULL)
HashScans = chk->hashsl_next;
else
last->hashsl_next = chk->hashsl_next;
pfree(chk);
}
void
_hash_adjscans(Relation rel, ItemPointer tid)
{
HashScanList l;
Oid relid;
relid = RelationGetRelid(rel);
for (l = HashScans; l != (HashScanList) NULL; l = l->hashsl_next)
{
if (relid == l->hashsl_scan->indexRelation->rd_id)
_hash_scandel(l->hashsl_scan, ItemPointerGetBlockNumber(tid),
ItemPointerGetOffsetNumber(tid));
}
}
static void
_hash_scandel(IndexScanDesc scan, BlockNumber blkno, OffsetNumber offno)
{
ItemPointer current;
ItemPointer mark;
Buffer buf;
Buffer metabuf;
HashScanOpaque so;
so = (HashScanOpaque) scan->opaque;
current = &(scan->currentItemData);
mark = &(scan->currentMarkData);
if (ItemPointerIsValid(current)
&& ItemPointerGetBlockNumber(current) == blkno
&& ItemPointerGetOffsetNumber(current) >= offno)
{
metabuf = _hash_getbuf(scan->indexRelation, HASH_METAPAGE, HASH_READ);
buf = so->hashso_curbuf;
_hash_step(scan, &buf, BackwardScanDirection, metabuf);
}
if (ItemPointerIsValid(mark)
&& ItemPointerGetBlockNumber(mark) == blkno
&& ItemPointerGetOffsetNumber(mark) >= offno)
{
/*
* The idea here is to exchange the current and mark positions,
* then step backwards (affecting current), then exchange again.
*/
ItemPointerData tmpitem;
Buffer tmpbuf;
tmpitem = *mark;
*mark = *current;
*current = tmpitem;
tmpbuf = so->hashso_mrkbuf;
so->hashso_mrkbuf = so->hashso_curbuf;
so->hashso_curbuf = tmpbuf;
metabuf = _hash_getbuf(scan->indexRelation, HASH_METAPAGE, HASH_READ);
buf = so->hashso_curbuf;
_hash_step(scan, &buf, BackwardScanDirection, metabuf);
tmpitem = *mark;
*mark = *current;
*current = tmpitem;
tmpbuf = so->hashso_mrkbuf;
so->hashso_mrkbuf = so->hashso_curbuf;
so->hashso_curbuf = tmpbuf;
}
}
|
