1 /*-------------------------------------------------------------------------
4 * routines to support manipulation of the pg_inherits relation
6 * Note: currently, this module only contains inquiry functions; the actual
7 * creation and deletion of pg_inherits entries is done in tablecmds.c.
8 * Perhaps someday that code should be moved here, but it'd have to be
9 * disentangled from other stuff such as pg_depend updates.
11 * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
12 * Portions Copyright (c) 1994, Regents of the University of California
16 * src/backend/catalog/pg_inherits.c
18 *-------------------------------------------------------------------------
22 #include "access/genam.h"
23 #include "access/heapam.h"
24 #include "access/htup_details.h"
25 #include "catalog/indexing.h"
26 #include "catalog/pg_inherits.h"
27 #include "catalog/pg_inherits_fn.h"
28 #include "parser/parse_type.h"
29 #include "storage/lmgr.h"
30 #include "utils/builtins.h"
31 #include "utils/fmgroids.h"
32 #include "utils/memutils.h"
33 #include "utils/syscache.h"
34 #include "utils/tqual.h"
37 * Entry of a hash table used in find_all_inheritors. See below.
39 typedef struct SeenRelsEntry
41 Oid rel_id; /* relation oid */
42 ListCell *numparents_cell; /* corresponding list cell */
46 * find_inheritance_children
48 * Returns a list containing the OIDs of all relations which
49 * inherit *directly* from the relation with OID 'parentrelId'.
51 * The specified lock type is acquired on each child relation (but not on the
52 * given rel; caller should already have locked it). If lockmode is NoLock
53 * then no locks are acquired, but caller must beware of race conditions
54 * against possible DROPs of child relations.
57 find_inheritance_children(Oid parentrelId, LOCKMODE lockmode)
63 HeapTuple inheritsTuple;
71 * Can skip the scan if pg_class shows the relation has never had a
74 if (!has_subclass(parentrelId))
78 * Scan pg_inherits and build a working array of subclass OIDs.
81 oidarr = (Oid *) palloc(maxoids * sizeof(Oid));
84 relation = heap_open(InheritsRelationId, AccessShareLock);
87 Anum_pg_inherits_inhparent,
88 BTEqualStrategyNumber, F_OIDEQ,
89 ObjectIdGetDatum(parentrelId));
91 scan = systable_beginscan(relation, InheritsParentIndexId, true,
94 while ((inheritsTuple = systable_getnext(scan)) != NULL)
96 inhrelid = ((Form_pg_inherits) GETSTRUCT(inheritsTuple))->inhrelid;
97 if (numoids >= maxoids)
100 oidarr = (Oid *) repalloc(oidarr, maxoids * sizeof(Oid));
102 oidarr[numoids++] = inhrelid;
105 systable_endscan(scan);
107 heap_close(relation, AccessShareLock);
110 * If we found more than one child, sort them by OID. This ensures
111 * reasonably consistent behavior regardless of the vagaries of an
112 * indexscan. This is important since we need to be sure all backends
113 * lock children in the same order to avoid needless deadlocks.
116 qsort(oidarr, numoids, sizeof(Oid), oid_cmp);
119 * Acquire locks and build the result list.
121 for (i = 0; i < numoids; i++)
123 inhrelid = oidarr[i];
125 if (lockmode != NoLock)
127 /* Get the lock to synchronize against concurrent drop */
128 LockRelationOid(inhrelid, lockmode);
131 * Now that we have the lock, double-check to see if the relation
132 * really exists or not. If not, assume it was dropped while we
133 * waited to acquire lock, and ignore it.
135 if (!SearchSysCacheExists1(RELOID, ObjectIdGetDatum(inhrelid)))
137 /* Release useless lock */
138 UnlockRelationOid(inhrelid, lockmode);
139 /* And ignore this relation */
144 list = lappend_oid(list, inhrelid);
154 * find_all_inheritors -
155 * Returns a list of relation OIDs including the given rel plus
156 * all relations that inherit from it, directly or indirectly.
157 * Optionally, it also returns the number of parents found for
158 * each such relation within the inheritance tree rooted at the
161 * The specified lock type is acquired on all child relations (but not on the
162 * given rel; caller should already have locked it). If lockmode is NoLock
163 * then no locks are acquired, but caller must beware of race conditions
164 * against possible DROPs of child relations.
167 find_all_inheritors(Oid parentrelId, LOCKMODE lockmode, List **numparents)
169 /* hash table for O(1) rel_oid -> rel_numparents cell lookup */
176 memset(&ctl, 0, sizeof(ctl));
177 ctl.keysize = sizeof(Oid);
178 ctl.entrysize = sizeof(SeenRelsEntry);
179 ctl.hcxt = CurrentMemoryContext;
181 seen_rels = hash_create("find_all_inheritors temporary table",
182 32, /* start small and extend */
184 HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
187 * We build a list starting with the given rel and adding all direct and
188 * indirect children. We can use a single list as both the record of
189 * already-found rels and the agenda of rels yet to be scanned for more
190 * children. This is a bit tricky but works because the foreach() macro
191 * doesn't fetch the next list element until the bottom of the loop.
193 rels_list = list_make1_oid(parentrelId);
194 rel_numparents = list_make1_int(0);
196 foreach(l, rels_list)
198 Oid currentrel = lfirst_oid(l);
199 List *currentchildren;
202 /* Get the direct children of this rel */
203 currentchildren = find_inheritance_children(currentrel, lockmode);
206 * Add to the queue only those children not already seen. This avoids
207 * making duplicate entries in case of multiple inheritance paths from
208 * the same parent. (It'll also keep us from getting into an infinite
209 * loop, though theoretically there can't be any cycles in the
210 * inheritance graph anyway.)
212 foreach(lc, currentchildren)
214 Oid child_oid = lfirst_oid(lc);
216 SeenRelsEntry *hash_entry;
218 hash_entry = hash_search(seen_rels, &child_oid, HASH_ENTER, &found);
221 /* if the rel is already there, bump number-of-parents counter */
222 lfirst_int(hash_entry->numparents_cell)++;
226 /* if it's not there, add it. expect 1 parent, initially. */
227 rels_list = lappend_oid(rels_list, child_oid);
228 rel_numparents = lappend_int(rel_numparents, 1);
229 hash_entry->numparents_cell = rel_numparents->tail;
235 *numparents = rel_numparents;
237 list_free(rel_numparents);
239 hash_destroy(seen_rels);
246 * has_subclass - does this relation have any children?
248 * In the current implementation, has_subclass returns whether a
249 * particular class *might* have a subclass. It will not return the
250 * correct result if a class had a subclass which was later dropped.
251 * This is because relhassubclass in pg_class is not updated immediately
252 * when a subclass is dropped, primarily because of concurrency concerns.
254 * Currently has_subclass is only used as an efficiency hack to skip
255 * unnecessary inheritance searches, so this is OK. Note that ANALYZE
256 * on a childless table will clean up the obsolete relhassubclass flag.
258 * Although this doesn't actually touch pg_inherits, it seems reasonable
259 * to keep it here since it's normally used with the other routines here.
262 has_subclass(Oid relationId)
267 tuple = SearchSysCache1(RELOID, ObjectIdGetDatum(relationId));
268 if (!HeapTupleIsValid(tuple))
269 elog(ERROR, "cache lookup failed for relation %u", relationId);
271 result = ((Form_pg_class) GETSTRUCT(tuple))->relhassubclass;
272 ReleaseSysCache(tuple);
277 * has_superclass - does this relation inherit from another? The caller
278 * should hold a lock on the given relation so that it can't be concurrently
279 * added to or removed from an inheritance hierarchy.
282 has_superclass(Oid relationId)
289 catalog = heap_open(InheritsRelationId, AccessShareLock);
290 ScanKeyInit(&skey, Anum_pg_inherits_inhrelid, BTEqualStrategyNumber,
291 F_OIDEQ, ObjectIdGetDatum(relationId));
292 scan = systable_beginscan(catalog, InheritsRelidSeqnoIndexId, true,
294 result = HeapTupleIsValid(systable_getnext(scan));
295 systable_endscan(scan);
296 heap_close(catalog, AccessShareLock);
302 * Given two type OIDs, determine whether the first is a complex type
303 * (class type) that inherits from the second.
305 * This essentially asks whether the first type is guaranteed to be coercible
306 * to the second. Therefore, we allow the first type to be a domain over a
307 * complex type that inherits from the second; that creates no difficulties.
308 * But the second type cannot be a domain.
311 typeInheritsFrom(Oid subclassTypeId, Oid superclassTypeId)
319 ListCell *queue_item;
321 /* We need to work with the associated relation OIDs */
322 subclassRelid = typeOrDomainTypeRelid(subclassTypeId);
323 if (subclassRelid == InvalidOid)
324 return false; /* not a complex type or domain over one */
325 superclassRelid = typeidTypeRelid(superclassTypeId);
326 if (superclassRelid == InvalidOid)
327 return false; /* not a complex type */
329 /* No point in searching if the superclass has no subclasses */
330 if (!has_subclass(superclassRelid))
334 * Begin the search at the relation itself, so add its relid to the queue.
336 queue = list_make1_oid(subclassRelid);
339 inhrel = heap_open(InheritsRelationId, AccessShareLock);
342 * Use queue to do a breadth-first traversal of the inheritance graph from
343 * the relid supplied up to the root. Notice that we append to the queue
344 * inside the loop --- this is okay because the foreach() macro doesn't
345 * advance queue_item until the next loop iteration begins.
347 foreach(queue_item, queue)
349 Oid this_relid = lfirst_oid(queue_item);
355 * If we've seen this relid already, skip it. This avoids extra work
356 * in multiple-inheritance scenarios, and also protects us from an
357 * infinite loop in case there is a cycle in pg_inherits (though
358 * theoretically that shouldn't happen).
360 if (list_member_oid(visited, this_relid))
364 * Okay, this is a not-yet-seen relid. Add it to the list of
365 * already-visited OIDs, then find all the types this relid inherits
366 * from and add them to the queue.
368 visited = lappend_oid(visited, this_relid);
371 Anum_pg_inherits_inhrelid,
372 BTEqualStrategyNumber, F_OIDEQ,
373 ObjectIdGetDatum(this_relid));
375 inhscan = systable_beginscan(inhrel, InheritsRelidSeqnoIndexId, true,
378 while ((inhtup = systable_getnext(inhscan)) != NULL)
380 Form_pg_inherits inh = (Form_pg_inherits) GETSTRUCT(inhtup);
381 Oid inhparent = inh->inhparent;
383 /* If this is the target superclass, we're done */
384 if (inhparent == superclassRelid)
390 /* Else add to queue */
391 queue = lappend_oid(queue, inhparent);
394 systable_endscan(inhscan);
401 heap_close(inhrel, AccessShareLock);