1/*-------------------------------------------------------------------------
2 *
3 * attoptcache.c
4 * Attribute options cache management.
5 *
6 * Attribute options are cached separately from the fixed-size portion of
7 * pg_attribute entries, which are handled by the relcache.
8 *
9 * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
10 * Portions Copyright (c) 1994, Regents of the University of California
11 *
12 * IDENTIFICATION
13 * src/backend/utils/cache/attoptcache.c
14 *
15 *-------------------------------------------------------------------------
16 */
17#include "postgres.h"
18
19#include "access/reloptions.h"
20#include "utils/attoptcache.h"
21#include "utils/catcache.h"
22#include "utils/hsearch.h"
23#include "utils/inval.h"
24#include "utils/syscache.h"
25
26
27/* Hash table for information about each attribute's options */
28static HTAB *AttoptCacheHash = NULL;
29
30/* attrelid and attnum form the lookup key, and must appear first */
31typedef struct
32{
33 Oid attrelid;
34 int attnum;
35} AttoptCacheKey;
36
37typedef struct
38{
39 AttoptCacheKey key; /* lookup key - must be first */
40 AttributeOpts *opts; /* options, or NULL if none */
41} AttoptCacheEntry;
42
43
44/*
45 * InvalidateAttoptCacheCallback
46 * Flush all cache entries when pg_attribute is updated.
47 *
48 * When pg_attribute is updated, we must flush the cache entry at least
49 * for that attribute. Currently, we just flush them all. Since attribute
50 * options are not currently used in performance-critical paths (such as
51 * query execution), this seems OK.
52 */
53static void
54InvalidateAttoptCacheCallback(Datum arg, int cacheid, uint32 hashvalue)
55{
56 HASH_SEQ_STATUS status;
57 AttoptCacheEntry *attopt;
58
59 hash_seq_init(&status, AttoptCacheHash);
60 while ((attopt = (AttoptCacheEntry *) hash_seq_search(&status)) != NULL)
61 {
62 if (attopt->opts)
63 pfree(attopt->opts);
64 if (hash_search(AttoptCacheHash,
65 (void *) &attopt->key,
66 HASH_REMOVE,
67 NULL) == NULL)
68 elog(ERROR, "hash table corrupted");
69 }
70}
71
72/*
73 * InitializeAttoptCache
74 * Initialize the attribute options cache.
75 */
76static void
77InitializeAttoptCache(void)
78{
79 HASHCTL ctl;
80
81 /* Initialize the hash table. */
82 MemSet(&ctl, 0, sizeof(ctl));
83 ctl.keysize = sizeof(AttoptCacheKey);
84 ctl.entrysize = sizeof(AttoptCacheEntry);
85 AttoptCacheHash =
86 hash_create("Attopt cache", 256, &ctl,
87 HASH_ELEM | HASH_BLOBS);
88
89 /* Make sure we've initialized CacheMemoryContext. */
90 if (!CacheMemoryContext)
91 CreateCacheMemoryContext();
92
93 /* Watch for invalidation events. */
94 CacheRegisterSyscacheCallback(ATTNUM,
95 InvalidateAttoptCacheCallback,
96 (Datum) 0);
97}
98
99/*
100 * get_attribute_options
101 * Fetch attribute options for a specified table OID.
102 */
103AttributeOpts *
104get_attribute_options(Oid attrelid, int attnum)
105{
106 AttoptCacheKey key;
107 AttoptCacheEntry *attopt;
108 AttributeOpts *result;
109 HeapTuple tp;
110
111 /* Find existing cache entry, if any. */
112 if (!AttoptCacheHash)
113 InitializeAttoptCache();
114 memset(&key, 0, sizeof(key)); /* make sure any padding bits are unset */
115 key.attrelid = attrelid;
116 key.attnum = attnum;
117 attopt =
118 (AttoptCacheEntry *) hash_search(AttoptCacheHash,
119 (void *) &key,
120 HASH_FIND,
121 NULL);
122
123 /* Not found in Attopt cache. Construct new cache entry. */
124 if (!attopt)
125 {
126 AttributeOpts *opts;
127
128 tp = SearchSysCache2(ATTNUM,
129 ObjectIdGetDatum(attrelid),
130 Int16GetDatum(attnum));
131
132 /*
133 * If we don't find a valid HeapTuple, it must mean someone has
134 * managed to request attribute details for a non-existent attribute.
135 * We treat that case as if no options were specified.
136 */
137 if (!HeapTupleIsValid(tp))
138 opts = NULL;
139 else
140 {
141 Datum datum;
142 bool isNull;
143
144 datum = SysCacheGetAttr(ATTNUM,
145 tp,
146 Anum_pg_attribute_attoptions,
147 &isNull);
148 if (isNull)
149 opts = NULL;
150 else
151 {
152 bytea *bytea_opts = attribute_reloptions(datum, false);
153
154 opts = MemoryContextAlloc(CacheMemoryContext,
155 VARSIZE(bytea_opts));
156 memcpy(opts, bytea_opts, VARSIZE(bytea_opts));
157 }
158 ReleaseSysCache(tp);
159 }
160
161 /*
162 * It's important to create the actual cache entry only after reading
163 * pg_attribute, since the read could cause a cache flush.
164 */
165 attopt = (AttoptCacheEntry *) hash_search(AttoptCacheHash,
166 (void *) &key,
167 HASH_ENTER,
168 NULL);
169 attopt->opts = opts;
170 }
171
172 /* Return results in caller's memory context. */
173 if (attopt->opts == NULL)
174 return NULL;
175 result = palloc(VARSIZE(attopt->opts));
176 memcpy(result, attopt->opts, VARSIZE(attopt->opts));
177 return result;
178}
179