PostgreSQL Source Code: src/backend/utils/misc/queryenvironment.c Source File

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queryenvironment.c
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1/*-------------------------------------------------------------------------
2 *
3 * queryenvironment.c
4 * Query environment, to store context-specific values like ephemeral named
5 * relations. Initial use is for named tuplestores for delta information
6 * from "normal" relations.
7 *
8 * The initial implementation uses a list because the number of such relations
9 * in any one context is expected to be very small. If that becomes a
10 * performance problem, the implementation can be changed with no other impact
11 * on callers, since this is an opaque structure. This is the reason to
12 * require a create function.
13 *
14 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
15 * Portions Copyright (c) 1994, Regents of the University of California
16 *
17 *
18 * IDENTIFICATION
19 * src/backend/utils/misc/queryenvironment.c
20 *
21 *-------------------------------------------------------------------------
22 */
23#include "postgres.h"
24
25#include "access/table.h"
26#include "utils/queryenvironment.h"
27#include "utils/rel.h"
28
29/*
30 * Private state of a query environment.
31 */
32 struct QueryEnvironment
33{
34 List *namedRelList;
35};
36
37
38QueryEnvironment *
39 create_queryEnv(void)
40{
41 return (QueryEnvironment *) palloc0(sizeof(QueryEnvironment));
42}
43
44EphemeralNamedRelationMetadata
45 get_visible_ENR_metadata(QueryEnvironment *queryEnv, const char *refname)
46{
47 EphemeralNamedRelation enr;
48
49 Assert(refname != NULL);
50
51 if (queryEnv == NULL)
52 return NULL;
53
54 enr = get_ENR(queryEnv, refname);
55
56 if (enr)
57 return &(enr->md);
58
59 return NULL;
60}
61
62/*
63 * Register a named relation for use in the given environment.
64 *
65 * If this is intended exclusively for planning purposes, the tstate field can
66 * be left NULL;
67 */
68void
69 register_ENR(QueryEnvironment *queryEnv, EphemeralNamedRelation enr)
70{
71 Assert(enr != NULL);
72 Assert(get_ENR(queryEnv, enr->md.name) == NULL);
73
74 queryEnv->namedRelList = lappend(queryEnv->namedRelList, enr);
75}
76
77/*
78 * Unregister an ephemeral relation by name. This will probably be a rarely
79 * used function, but seems like it should be provided "just in case".
80 */
81void
82 unregister_ENR(QueryEnvironment *queryEnv, const char *name)
83{
84 EphemeralNamedRelation match;
85
86 match = get_ENR(queryEnv, name);
87 if (match)
88 queryEnv->namedRelList = list_delete(queryEnv->namedRelList, match);
89}
90
91/*
92 * This returns an ENR if there is a name match in the given collection. It
93 * must quietly return NULL if no match is found.
94 */
95EphemeralNamedRelation
96 get_ENR(QueryEnvironment *queryEnv, const char *name)
97{
98 ListCell *lc;
99
100 Assert(name != NULL);
101
102 if (queryEnv == NULL)
103 return NULL;
104
105 foreach(lc, queryEnv->namedRelList)
106 {
107 EphemeralNamedRelation enr = (EphemeralNamedRelation) lfirst(lc);
108
109 if (strcmp(enr->md.name, name) == 0)
110 return enr;
111 }
112
113 return NULL;
114}
115
116/*
117 * Gets the TupleDesc for a Ephemeral Named Relation, based on which field was
118 * filled.
119 *
120 * When the TupleDesc is based on a relation from the catalogs, we count on
121 * that relation being used at the same time, so that appropriate locks will
122 * already be held. Locking here would be too late anyway.
123 */
124TupleDesc
125 ENRMetadataGetTupDesc(EphemeralNamedRelationMetadata enrmd)
126{
127 TupleDesc tupdesc;
128
129 /* One, and only one, of these fields must be filled. */
130 Assert((enrmd->reliddesc == InvalidOid) != (enrmd->tupdesc == NULL));
131
132 if (enrmd->tupdesc != NULL)
133 tupdesc = enrmd->tupdesc;
134 else
135 {
136 Relation relation;
137
138 relation = table_open(enrmd->reliddesc, NoLock);
139 tupdesc = relation->rd_att;
140 table_close(relation, NoLock);
141 }
142
143 return tupdesc;
144}
Assert(PointerIsAligned(start, uint64))
List * lappend(List *list, void *datum)
Definition: list.c:339
List * list_delete(List *list, void *datum)
Definition: list.c:853
#define NoLock
Definition: lockdefs.h:34
void * palloc0(Size size)
Definition: mcxt.c:1395
#define lfirst(lc)
Definition: pg_list.h:172
#define InvalidOid
Definition: postgres_ext.h:37
TupleDesc ENRMetadataGetTupDesc(EphemeralNamedRelationMetadata enrmd)
EphemeralNamedRelation get_ENR(QueryEnvironment *queryEnv, const char *name)
EphemeralNamedRelationMetadata get_visible_ENR_metadata(QueryEnvironment *queryEnv, const char *refname)
void unregister_ENR(QueryEnvironment *queryEnv, const char *name)
QueryEnvironment * create_queryEnv(void)
void register_ENR(QueryEnvironment *queryEnv, EphemeralNamedRelation enr)
EphemeralNamedRelationData * EphemeralNamedRelation
EphemeralNamedRelationMetadataData md
Definition: pg_list.h:54
Definition: rel.h:56
TupleDesc rd_att
Definition: rel.h:112
void table_close(Relation relation, LOCKMODE lockmode)
Definition: table.c:126
Relation table_open(Oid relationId, LOCKMODE lockmode)
Definition: table.c:40
Definition: pg_list.h:46
const char * name

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