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4baaf863ec
Backpatch certain files through 9.0
375 lines
10 KiB
C
375 lines
10 KiB
C
/*-------------------------------------------------------------------------
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*
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* pg_inherits.c
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* routines to support manipulation of the pg_inherits relation
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*
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* Note: currently, this module only contains inquiry functions; the actual
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* creation and deletion of pg_inherits entries is done in tablecmds.c.
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* Perhaps someday that code should be moved here, but it'd have to be
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* disentangled from other stuff such as pg_depend updates.
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*
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* Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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*
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* IDENTIFICATION
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* src/backend/catalog/pg_inherits.c
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "access/genam.h"
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#include "access/heapam.h"
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#include "access/htup_details.h"
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#include "catalog/indexing.h"
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#include "catalog/pg_inherits.h"
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#include "catalog/pg_inherits_fn.h"
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#include "parser/parse_type.h"
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#include "storage/lmgr.h"
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#include "utils/fmgroids.h"
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#include "utils/syscache.h"
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#include "utils/tqual.h"
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static int oid_cmp(const void *p1, const void *p2);
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/*
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* find_inheritance_children
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*
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* Returns a list containing the OIDs of all relations which
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* inherit *directly* from the relation with OID 'parentrelId'.
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*
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* The specified lock type is acquired on each child relation (but not on the
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* given rel; caller should already have locked it). If lockmode is NoLock
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* then no locks are acquired, but caller must beware of race conditions
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* against possible DROPs of child relations.
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*/
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List *
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find_inheritance_children(Oid parentrelId, LOCKMODE lockmode)
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{
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List *list = NIL;
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Relation relation;
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SysScanDesc scan;
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ScanKeyData key[1];
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HeapTuple inheritsTuple;
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Oid inhrelid;
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Oid *oidarr;
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int maxoids,
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numoids,
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i;
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/*
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* Can skip the scan if pg_class shows the relation has never had a
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* subclass.
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*/
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if (!has_subclass(parentrelId))
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return NIL;
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/*
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* Scan pg_inherits and build a working array of subclass OIDs.
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*/
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maxoids = 32;
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oidarr = (Oid *) palloc(maxoids * sizeof(Oid));
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numoids = 0;
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relation = heap_open(InheritsRelationId, AccessShareLock);
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ScanKeyInit(&key[0],
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Anum_pg_inherits_inhparent,
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BTEqualStrategyNumber, F_OIDEQ,
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ObjectIdGetDatum(parentrelId));
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scan = systable_beginscan(relation, InheritsParentIndexId, true,
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NULL, 1, key);
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while ((inheritsTuple = systable_getnext(scan)) != NULL)
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{
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inhrelid = ((Form_pg_inherits) GETSTRUCT(inheritsTuple))->inhrelid;
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if (numoids >= maxoids)
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{
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maxoids *= 2;
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oidarr = (Oid *) repalloc(oidarr, maxoids * sizeof(Oid));
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}
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oidarr[numoids++] = inhrelid;
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}
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systable_endscan(scan);
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heap_close(relation, AccessShareLock);
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/*
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* If we found more than one child, sort them by OID. This ensures
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* reasonably consistent behavior regardless of the vagaries of an
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* indexscan. This is important since we need to be sure all backends
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* lock children in the same order to avoid needless deadlocks.
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*/
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if (numoids > 1)
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qsort(oidarr, numoids, sizeof(Oid), oid_cmp);
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/*
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* Acquire locks and build the result list.
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*/
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for (i = 0; i < numoids; i++)
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{
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inhrelid = oidarr[i];
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if (lockmode != NoLock)
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{
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/* Get the lock to synchronize against concurrent drop */
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LockRelationOid(inhrelid, lockmode);
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/*
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* Now that we have the lock, double-check to see if the relation
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* really exists or not. If not, assume it was dropped while we
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* waited to acquire lock, and ignore it.
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*/
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if (!SearchSysCacheExists1(RELOID, ObjectIdGetDatum(inhrelid)))
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{
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/* Release useless lock */
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UnlockRelationOid(inhrelid, lockmode);
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/* And ignore this relation */
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continue;
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}
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}
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list = lappend_oid(list, inhrelid);
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}
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pfree(oidarr);
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return list;
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}
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/*
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* find_all_inheritors -
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* Returns a list of relation OIDs including the given rel plus
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* all relations that inherit from it, directly or indirectly.
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* Optionally, it also returns the number of parents found for
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* each such relation within the inheritance tree rooted at the
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* given rel.
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*
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* The specified lock type is acquired on all child relations (but not on the
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* given rel; caller should already have locked it). If lockmode is NoLock
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* then no locks are acquired, but caller must beware of race conditions
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* against possible DROPs of child relations.
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*/
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List *
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find_all_inheritors(Oid parentrelId, LOCKMODE lockmode, List **numparents)
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{
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List *rels_list,
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*rel_numparents;
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ListCell *l;
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/*
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* We build a list starting with the given rel and adding all direct and
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* indirect children. We can use a single list as both the record of
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* already-found rels and the agenda of rels yet to be scanned for more
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* children. This is a bit tricky but works because the foreach() macro
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* doesn't fetch the next list element until the bottom of the loop.
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*/
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rels_list = list_make1_oid(parentrelId);
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rel_numparents = list_make1_int(0);
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foreach(l, rels_list)
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{
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Oid currentrel = lfirst_oid(l);
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List *currentchildren;
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ListCell *lc;
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/* Get the direct children of this rel */
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currentchildren = find_inheritance_children(currentrel, lockmode);
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/*
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* Add to the queue only those children not already seen. This avoids
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* making duplicate entries in case of multiple inheritance paths from
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* the same parent. (It'll also keep us from getting into an infinite
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* loop, though theoretically there can't be any cycles in the
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* inheritance graph anyway.)
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*/
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foreach(lc, currentchildren)
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{
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Oid child_oid = lfirst_oid(lc);
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bool found = false;
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ListCell *lo;
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ListCell *li;
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/* if the rel is already there, bump number-of-parents counter */
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forboth(lo, rels_list, li, rel_numparents)
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{
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if (lfirst_oid(lo) == child_oid)
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{
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lfirst_int(li)++;
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found = true;
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break;
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}
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}
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/* if it's not there, add it. expect 1 parent, initially. */
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if (!found)
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{
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rels_list = lappend_oid(rels_list, child_oid);
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rel_numparents = lappend_int(rel_numparents, 1);
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}
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}
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}
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if (numparents)
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*numparents = rel_numparents;
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else
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list_free(rel_numparents);
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return rels_list;
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}
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/*
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* has_subclass - does this relation have any children?
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*
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* In the current implementation, has_subclass returns whether a
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* particular class *might* have a subclass. It will not return the
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* correct result if a class had a subclass which was later dropped.
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* This is because relhassubclass in pg_class is not updated immediately
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* when a subclass is dropped, primarily because of concurrency concerns.
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*
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* Currently has_subclass is only used as an efficiency hack to skip
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* unnecessary inheritance searches, so this is OK. Note that ANALYZE
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* on a childless table will clean up the obsolete relhassubclass flag.
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*
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* Although this doesn't actually touch pg_inherits, it seems reasonable
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* to keep it here since it's normally used with the other routines here.
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*/
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bool
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has_subclass(Oid relationId)
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{
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HeapTuple tuple;
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bool result;
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tuple = SearchSysCache1(RELOID, ObjectIdGetDatum(relationId));
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if (!HeapTupleIsValid(tuple))
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elog(ERROR, "cache lookup failed for relation %u", relationId);
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result = ((Form_pg_class) GETSTRUCT(tuple))->relhassubclass;
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ReleaseSysCache(tuple);
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return result;
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}
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/*
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* Given two type OIDs, determine whether the first is a complex type
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* (class type) that inherits from the second.
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*/
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bool
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typeInheritsFrom(Oid subclassTypeId, Oid superclassTypeId)
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{
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bool result = false;
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Oid subclassRelid;
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Oid superclassRelid;
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Relation inhrel;
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List *visited,
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*queue;
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ListCell *queue_item;
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/* We need to work with the associated relation OIDs */
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subclassRelid = typeidTypeRelid(subclassTypeId);
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if (subclassRelid == InvalidOid)
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return false; /* not a complex type */
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superclassRelid = typeidTypeRelid(superclassTypeId);
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if (superclassRelid == InvalidOid)
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return false; /* not a complex type */
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/* No point in searching if the superclass has no subclasses */
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if (!has_subclass(superclassRelid))
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return false;
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/*
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* Begin the search at the relation itself, so add its relid to the queue.
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*/
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queue = list_make1_oid(subclassRelid);
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visited = NIL;
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inhrel = heap_open(InheritsRelationId, AccessShareLock);
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/*
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* Use queue to do a breadth-first traversal of the inheritance graph from
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* the relid supplied up to the root. Notice that we append to the queue
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* inside the loop --- this is okay because the foreach() macro doesn't
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* advance queue_item until the next loop iteration begins.
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*/
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foreach(queue_item, queue)
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{
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Oid this_relid = lfirst_oid(queue_item);
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ScanKeyData skey;
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SysScanDesc inhscan;
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HeapTuple inhtup;
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/*
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* If we've seen this relid already, skip it. This avoids extra work
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* in multiple-inheritance scenarios, and also protects us from an
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* infinite loop in case there is a cycle in pg_inherits (though
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* theoretically that shouldn't happen).
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*/
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if (list_member_oid(visited, this_relid))
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continue;
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/*
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* Okay, this is a not-yet-seen relid. Add it to the list of
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* already-visited OIDs, then find all the types this relid inherits
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* from and add them to the queue.
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*/
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visited = lappend_oid(visited, this_relid);
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ScanKeyInit(&skey,
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Anum_pg_inherits_inhrelid,
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BTEqualStrategyNumber, F_OIDEQ,
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ObjectIdGetDatum(this_relid));
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inhscan = systable_beginscan(inhrel, InheritsRelidSeqnoIndexId, true,
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NULL, 1, &skey);
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while ((inhtup = systable_getnext(inhscan)) != NULL)
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{
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Form_pg_inherits inh = (Form_pg_inherits) GETSTRUCT(inhtup);
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Oid inhparent = inh->inhparent;
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/* If this is the target superclass, we're done */
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if (inhparent == superclassRelid)
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{
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result = true;
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break;
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}
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/* Else add to queue */
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queue = lappend_oid(queue, inhparent);
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}
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systable_endscan(inhscan);
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if (result)
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break;
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}
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/* clean up ... */
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heap_close(inhrel, AccessShareLock);
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list_free(visited);
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list_free(queue);
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return result;
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}
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/* qsort comparison function */
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static int
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oid_cmp(const void *p1, const void *p2)
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{
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Oid v1 = *((const Oid *) p1);
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Oid v2 = *((const Oid *) p2);
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if (v1 < v2)
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return -1;
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if (v1 > v2)
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return 1;
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return 0;
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}
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