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shippable.c
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1 /*-------------------------------------------------------------------------
2  *
3  * shippable.c
4  * Determine which database objects are shippable to a remote server.
5  *
6  * We need to determine whether particular functions, operators, and indeed
7  * data types are shippable to a remote server for execution --- that is,
8  * do they exist and have the same behavior remotely as they do locally?
9  * Built-in objects are generally considered shippable. Other objects can
10  * be shipped if they are declared as such by the user.
11  *
12  * Note: there are additional filter rules that prevent shipping mutable
13  * functions or functions using nonportable collations. Those considerations
14  * need not be accounted for here.
15  *
16  * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
17  *
18  * IDENTIFICATION
19  * contrib/postgres_fdw/shippable.c
20  *
21  *-------------------------------------------------------------------------
22  */
23 
24 #include "postgres.h"
25 
26 #include "access/transam.h"
27 #include "catalog/dependency.h"
28 #include "postgres_fdw.h"
29 #include "utils/hsearch.h"
30 #include "utils/inval.h"
31 #include "utils/syscache.h"
32 
33 /* Hash table for caching the results of shippability lookups */
34 static HTAB *ShippableCacheHash = NULL;
35 
36 /*
37  * Hash key for shippability lookups. We include the FDW server OID because
38  * decisions may differ per-server. Otherwise, objects are identified by
39  * their (local!) OID and catalog OID.
40  */
41 typedef struct
42 {
43  /* XXX we assume this struct contains no padding bytes */
44  Oid objid; /* function/operator/type OID */
45  Oid classid; /* OID of its catalog (pg_proc, etc) */
46  Oid serverid; /* FDW server we are concerned with */
48 
49 typedef struct
50 {
51  ShippableCacheKey key; /* hash key - must be first */
52  bool shippable;
54 
55 
56 /*
57  * Flush cache entries when pg_foreign_server is updated.
58  *
59  * We do this because of the possibility of ALTER SERVER being used to change
60  * a server's extensions option. We do not currently bother to check whether
61  * objects' extension membership changes once a shippability decision has been
62  * made for them, however.
63  */
64 static void
66 {
68  ShippableCacheEntry *entry;
69 
70  /*
71  * In principle we could flush only cache entries relating to the
72  * pg_foreign_server entry being outdated; but that would be more
73  * complicated, and it's probably not worth the trouble. So for now, just
74  * flush all entries.
75  */
76  hash_seq_init(&status, ShippableCacheHash);
77  while ((entry = (ShippableCacheEntry *) hash_seq_search(&status)) != NULL)
78  {
79  if (hash_search(ShippableCacheHash,
80  (void *) &entry->key,
82  NULL) == NULL)
83  elog(ERROR, "hash table corrupted");
84  }
85 }
86 
87 /*
88  * Initialize the backend-lifespan cache of shippability decisions.
89  */
90 static void
92 {
93  HASHCTL ctl;
94 
95  /* Create the hash table. */
96  ctl.keysize = sizeof(ShippableCacheKey);
97  ctl.entrysize = sizeof(ShippableCacheEntry);
98  ShippableCacheHash =
99  hash_create("Shippability cache", 256, &ctl, HASH_ELEM | HASH_BLOBS);
100 
101  /* Set up invalidation callback on pg_foreign_server. */
104  (Datum) 0);
105 }
106 
107 /*
108  * Returns true if given object (operator/function/type) is shippable
109  * according to the server options.
110  *
111  * Right now "shippability" is exclusively a function of whether the object
112  * belongs to an extension declared by the user. In the future we could
113  * additionally have a list of functions/operators declared one at a time.
114  */
115 static bool
116 lookup_shippable(Oid objectId, Oid classId, PgFdwRelationInfo *fpinfo)
117 {
118  Oid extensionOid;
119 
120  /*
121  * Is object a member of some extension? (Note: this is a fairly
122  * expensive lookup, which is why we try to cache the results.)
123  */
124  extensionOid = getExtensionOfObject(classId, objectId);
125 
126  /* If so, is that extension in fpinfo->shippable_extensions? */
127  if (OidIsValid(extensionOid) &&
128  list_member_oid(fpinfo->shippable_extensions, extensionOid))
129  return true;
130 
131  return false;
132 }
133 
134 /*
135  * Return true if given object is one of PostgreSQL's built-in objects.
136  *
137  * We use FirstGenbkiObjectId as the cutoff, so that we only consider
138  * objects with hand-assigned OIDs to be "built in", not for instance any
139  * function or type defined in the information_schema.
140  *
141  * Our constraints for dealing with types are tighter than they are for
142  * functions or operators: we want to accept only types that are in pg_catalog,
143  * else deparse_type_name might incorrectly fail to schema-qualify their names.
144  * Thus we must exclude information_schema types.
145  *
146  * XXX there is a problem with this, which is that the set of built-in
147  * objects expands over time. Something that is built-in to us might not
148  * be known to the remote server, if it's of an older version. But keeping
149  * track of that would be a huge exercise.
150  */
151 bool
152 is_builtin(Oid objectId)
153 {
154  return (objectId < FirstGenbkiObjectId);
155 }
156 
157 /*
158  * is_shippable
159  * Is this object (function/operator/type) shippable to foreign server?
160  */
161 bool
162 is_shippable(Oid objectId, Oid classId, PgFdwRelationInfo *fpinfo)
163 {
165  ShippableCacheEntry *entry;
166 
167  /* Built-in objects are presumed shippable. */
168  if (is_builtin(objectId))
169  return true;
170 
171  /* Otherwise, give up if user hasn't specified any shippable extensions. */
172  if (fpinfo->shippable_extensions == NIL)
173  return false;
174 
175  /* Initialize cache if first time through. */
176  if (!ShippableCacheHash)
178 
179  /* Set up cache hash key */
180  key.objid = objectId;
181  key.classid = classId;
182  key.serverid = fpinfo->server->serverid;
183 
184  /* See if we already cached the result. */
185  entry = (ShippableCacheEntry *)
186  hash_search(ShippableCacheHash,
187  (void *) &key,
188  HASH_FIND,
189  NULL);
190 
191  if (!entry)
192  {
193  /* Not found in cache, so perform shippability lookup. */
194  bool shippable = lookup_shippable(objectId, classId, fpinfo);
195 
196  /*
197  * Don't create a new hash entry until *after* we have the shippable
198  * result in hand, as the underlying catalog lookups might trigger a
199  * cache invalidation.
200  */
201  entry = (ShippableCacheEntry *)
202  hash_search(ShippableCacheHash,
203  (void *) &key,
204  HASH_ENTER,
205  NULL);
206 
207  entry->shippable = shippable;
208  }
209 
210  return entry->shippable;
211 }
#define NIL
Definition: pg_list.h:65
Oid getExtensionOfObject(Oid classId, Oid objectId)
Definition: pg_depend.c:701
bool is_builtin(Oid objectId)
Definition: shippable.c:152
#define HASH_ELEM
Definition: hsearch.h:95
ForeignServer * server
Definition: postgres_fdw.h:86
Size entrysize
Definition: hsearch.h:76
void * hash_search(HTAB *hashp, const void *keyPtr, HASHACTION action, bool *foundPtr)
Definition: dynahash.c:954
unsigned int Oid
Definition: postgres_ext.h:31
#define OidIsValid(objectId)
Definition: c.h:710
static void InitializeShippableCache(void)
Definition: shippable.c:91
static bool lookup_shippable(Oid objectId, Oid classId, PgFdwRelationInfo *fpinfo)
Definition: shippable.c:116
Definition: dynahash.c:219
#define ERROR
Definition: elog.h:46
HTAB * hash_create(const char *tabname, long nelem, const HASHCTL *info, int flags)
Definition: dynahash.c:349
unsigned int uint32
Definition: c.h:441
#define HASH_BLOBS
Definition: hsearch.h:97
void CacheRegisterSyscacheCallback(int cacheid, SyscacheCallbackFunction func, Datum arg)
Definition: inval.c:1435
uintptr_t Datum
Definition: postgres.h:411
bool is_shippable(Oid objectId, Oid classId, PgFdwRelationInfo *fpinfo)
Definition: shippable.c:162
Size keysize
Definition: hsearch.h:75
bool list_member_oid(const List *list, Oid datum)
Definition: list.c:689
void * hash_seq_search(HASH_SEQ_STATUS *status)
Definition: dynahash.c:1436
void hash_seq_init(HASH_SEQ_STATUS *status, HTAB *hashp)
Definition: dynahash.c:1426
static void InvalidateShippableCacheCallback(Datum arg, int cacheid, uint32 hashvalue)
Definition: shippable.c:65
#define FirstGenbkiObjectId
Definition: transam.h:188
static HTAB * ShippableCacheHash
Definition: shippable.c:34
#define elog(elevel,...)
Definition: elog.h:232
void * arg
ShippableCacheKey key
Definition: shippable.c:51
static void static void status(const char *fmt,...) pg_attribute_printf(1
Definition: pg_regress.c:227
List * shippable_extensions
Definition: postgres_fdw.h:81
Oid serverid
Definition: foreign.h:36