pg_depend.c

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/*-------------------------------------------------------------------------
 *
 * pg_depend.c
 *    routines to support manipulation of the pg_depend relation
 *
 * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/catalog/pg_depend.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include "access/genam.h"
#include "access/htup_details.h"
#include "access/table.h"
#include "catalog/catalog.h"
#include "catalog/dependency.h"
#include "catalog/indexing.h"
#include "catalog/pg_constraint.h"
#include "catalog/pg_depend.h"
#include "catalog/pg_extension.h"
#include "commands/extension.h"
#include "miscadmin.h"
#include "utils/fmgroids.h"
#include "utils/lsyscache.h"
#include "utils/rel.h"
 
 
static bool isObjectPinned(const ObjectAddress *object);
 
 
/*
 * Record a dependency between 2 objects via their respective objectAddress.
 * The first argument is the dependent object, the second the one it
 * references.
 *
 * This simply creates an entry in pg_depend, without any other processing.
 */
void
recordDependencyOn(const ObjectAddress *depender,
                   const ObjectAddress *referenced,
                   DependencyType behavior)
{
    recordMultipleDependencies(depender, referenced, 1, behavior);
}
 
/*
 * Record multiple dependencies (of the same kind) for a single dependent
 * object.  This has a little less overhead than recording each separately.
 */
void
recordMultipleDependencies(const ObjectAddress *depender,
                           const ObjectAddress *referenced,
                           int nreferenced,
                           DependencyType behavior)
{
    Relation    dependDesc;
    CatalogIndexState indstate;
    TupleTableSlot **slot;
    int         i,
                max_slots,
                slot_init_count,
                slot_stored_count;
 
    if (nreferenced <= 0)
        return;                 /* nothing to do */
 
    /*
     * During bootstrap, do nothing since pg_depend may not exist yet.
     *
     * Objects created during bootstrap are most likely pinned, and the few
     * that are not do not have dependencies on each other, so that there
     * would be no need to make a pg_depend entry anyway.
     */
    if (IsBootstrapProcessingMode())
        return;
 
    dependDesc = table_open(DependRelationId, RowExclusiveLock);
 
    /*
     * Allocate the slots to use, but delay costly initialization until we
     * know that they will be used.
     */
    max_slots = Min(nreferenced,
                    MAX_CATALOG_MULTI_INSERT_BYTES / sizeof(FormData_pg_depend));
    slot = palloc(sizeof(TupleTableSlot *) * max_slots);
 
    /* Don't open indexes unless we need to make an update */
    indstate = NULL;
 
    /* number of slots currently storing tuples */
    slot_stored_count = 0;
    /* number of slots currently initialized */
    slot_init_count = 0;
    for (i = 0; i < nreferenced; i++, referenced++)
    {
        /*
         * If the referenced object is pinned by the system, there's no real
         * need to record dependencies on it.  This saves lots of space in
         * pg_depend, so it's worth the time taken to check.
         */
        if (isObjectPinned(referenced))
            continue;
 
        if (slot_init_count < max_slots)
        {
            slot[slot_stored_count] = MakeSingleTupleTableSlot(RelationGetDescr(dependDesc),
                                                               &TTSOpsHeapTuple);
            slot_init_count++;
        }
 
        ExecClearTuple(slot[slot_stored_count]);
 
        /*
         * Record the dependency.  Note we don't bother to check for duplicate
         * dependencies; there's no harm in them.
         */
        slot[slot_stored_count]->tts_values[Anum_pg_depend_refclassid - 1] = ObjectIdGetDatum(referenced->classId);
        slot[slot_stored_count]->tts_values[Anum_pg_depend_refobjid - 1] = ObjectIdGetDatum(referenced->objectId);
        slot[slot_stored_count]->tts_values[Anum_pg_depend_refobjsubid - 1] = Int32GetDatum(referenced->objectSubId);
        slot[slot_stored_count]->tts_values[Anum_pg_depend_deptype - 1] = CharGetDatum((char) behavior);
        slot[slot_stored_count]->tts_values[Anum_pg_depend_classid - 1] = ObjectIdGetDatum(depender->classId);
        slot[slot_stored_count]->tts_values[Anum_pg_depend_objid - 1] = ObjectIdGetDatum(depender->objectId);
        slot[slot_stored_count]->tts_values[Anum_pg_depend_objsubid - 1] = Int32GetDatum(depender->objectSubId);
 
        memset(slot[slot_stored_count]->tts_isnull, false,
               slot[slot_stored_count]->tts_tupleDescriptor->natts * sizeof(bool));
 
        ExecStoreVirtualTuple(slot[slot_stored_count]);
        slot_stored_count++;
 
        /* If slots are full, insert a batch of tuples */
        if (slot_stored_count == max_slots)
        {
            /* fetch index info only when we know we need it */
            if (indstate == NULL)
                indstate = CatalogOpenIndexes(dependDesc);
 
            CatalogTuplesMultiInsertWithInfo(dependDesc, slot, slot_stored_count,
                                             indstate);
            slot_stored_count = 0;
        }
    }
 
    /* Insert any tuples left in the buffer */
    if (slot_stored_count > 0)
    {
        /* fetch index info only when we know we need it */
        if (indstate == NULL)
            indstate = CatalogOpenIndexes(dependDesc);
 
        CatalogTuplesMultiInsertWithInfo(dependDesc, slot, slot_stored_count,
                                         indstate);
    }
 
    if (indstate != NULL)
        CatalogCloseIndexes(indstate);
 
    table_close(dependDesc, RowExclusiveLock);
 
    /* Drop only the number of slots used */
    for (i = 0; i < slot_init_count; i++)
        ExecDropSingleTupleTableSlot(slot[i]);
    pfree(slot);
}
 
/*
 * If we are executing a CREATE EXTENSION operation, mark the given object
 * as being a member of the extension, or check that it already is one.
 * Otherwise, do nothing.
 *
 * This must be called during creation of any user-definable object type
 * that could be a member of an extension.
 *
 * isReplace must be true if the object already existed, and false if it is
 * newly created.  In the former case we insist that it already be a member
 * of the current extension.  In the latter case we can skip checking whether
 * it is already a member of any extension.
 *
 * Note: isReplace = true is typically used when updating an object in
 * CREATE OR REPLACE and similar commands.  We used to allow the target
 * object to not already be an extension member, instead silently absorbing
 * it into the current extension.  However, this was both error-prone
 * (extensions might accidentally overwrite free-standing objects) and
 * a security hazard (since the object would retain its previous ownership).
 */
void
recordDependencyOnCurrentExtension(const ObjectAddress *object,
                                   bool isReplace)
{
    /* Only whole objects can be extension members */
    Assert(object->objectSubId == 0);
 
    if (creating_extension)
    {
        ObjectAddress extension;
 
        /* Only need to check for existing membership if isReplace */
        if (isReplace)
        {
            Oid         oldext;
 
            /*
             * Side note: these catalog lookups are safe only because the
             * object is a pre-existing one.  In the not-isReplace case, the
             * caller has most likely not yet done a CommandCounterIncrement
             * that would make the new object visible.
             */
            oldext = getExtensionOfObject(object->classId, object->objectId);
            if (OidIsValid(oldext))
            {
                /* If already a member of this extension, nothing to do */
                if (oldext == CurrentExtensionObject)
                    return;
                /* Already a member of some other extension, so reject */
                ereport(ERROR,
                        (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                         errmsg("%s is already a member of extension \"%s\"",
                                getObjectDescription(object, false),
                                get_extension_name(oldext))));
            }
            /* It's a free-standing object, so reject */
            ereport(ERROR,
                    (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                     errmsg("%s is not a member of extension \"%s\"",
                            getObjectDescription(object, false),
                            get_extension_name(CurrentExtensionObject)),
                     errdetail("An extension is not allowed to replace an object that it does not own.")));
        }
 
        /* OK, record it as a member of CurrentExtensionObject */
        extension.classId = ExtensionRelationId;
        extension.objectId = CurrentExtensionObject;
        extension.objectSubId = 0;
 
        recordDependencyOn(object, &extension, DEPENDENCY_EXTENSION);
    }
}
 
/*
 * If we are executing a CREATE EXTENSION operation, check that the given
 * object is a member of the extension, and throw an error if it isn't.
 * Otherwise, do nothing.
 *
 * This must be called whenever a CREATE IF NOT EXISTS operation (for an
 * object type that can be an extension member) has found that an object of
 * the desired name already exists.  It is insecure for an extension to use
 * IF NOT EXISTS except when the conflicting object is already an extension
 * member; otherwise a hostile user could substitute an object with arbitrary
 * properties.
 */
void
checkMembershipInCurrentExtension(const ObjectAddress *object)
{
    /*
     * This is actually the same condition tested in
     * recordDependencyOnCurrentExtension; but we want to issue a
     * differently-worded error, and anyway it would be pretty confusing to
     * call recordDependencyOnCurrentExtension in these circumstances.
     */
 
    /* Only whole objects can be extension members */
    Assert(object->objectSubId == 0);
 
    if (creating_extension)
    {
        Oid         oldext;
 
        oldext = getExtensionOfObject(object->classId, object->objectId);
        /* If already a member of this extension, OK */
        if (oldext == CurrentExtensionObject)
            return;
        /* Else complain */
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("%s is not a member of extension \"%s\"",
                        getObjectDescription(object, false),
                        get_extension_name(CurrentExtensionObject)),
                 errdetail("An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.")));
    }
}
 
/*
 * deleteDependencyRecordsFor -- delete all records with given depender
 * classId/objectId.  Returns the number of records deleted.
 *
 * This is used when redefining an existing object.  Links leading to the
 * object do not change, and links leading from it will be recreated
 * (possibly with some differences from before).
 *
 * If skipExtensionDeps is true, we do not delete any dependencies that
 * show that the given object is a member of an extension.  This avoids
 * needing a lot of extra logic to fetch and recreate that dependency.
 */
long
deleteDependencyRecordsFor(Oid classId, Oid objectId,
                           bool skipExtensionDeps)
{
    long        count = 0;
    Relation    depRel;
    ScanKeyData key[2];
    SysScanDesc scan;
    HeapTuple   tup;
 
    depRel = table_open(DependRelationId, RowExclusiveLock);
 
    ScanKeyInit(&key[0],
                Anum_pg_depend_classid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(classId));
    ScanKeyInit(&key[1],
                Anum_pg_depend_objid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(objectId));
 
    scan = systable_beginscan(depRel, DependDependerIndexId, true,
                              NULL, 2, key);
 
    while (HeapTupleIsValid(tup = systable_getnext(scan)))
    {
        if (skipExtensionDeps &&
            ((Form_pg_depend) GETSTRUCT(tup))->deptype == DEPENDENCY_EXTENSION)
            continue;
 
        CatalogTupleDelete(depRel, &tup->t_self);
        count++;
    }
 
    systable_endscan(scan);
 
    table_close(depRel, RowExclusiveLock);
 
    return count;
}
 
/*
 * deleteDependencyRecordsForClass -- delete all records with given depender
 * classId/objectId, dependee classId, and deptype.
 * Returns the number of records deleted.
 *
 * This is a variant of deleteDependencyRecordsFor, useful when revoking
 * an object property that is expressed by a dependency record (such as
 * extension membership).
 */
long
deleteDependencyRecordsForClass(Oid classId, Oid objectId,
                                Oid refclassId, char deptype)
{
    long        count = 0;
    Relation    depRel;
    ScanKeyData key[2];
    SysScanDesc scan;
    HeapTuple   tup;
 
    depRel = table_open(DependRelationId, RowExclusiveLock);
 
    ScanKeyInit(&key[0],
                Anum_pg_depend_classid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(classId));
    ScanKeyInit(&key[1],
                Anum_pg_depend_objid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(objectId));
 
    scan = systable_beginscan(depRel, DependDependerIndexId, true,
                              NULL, 2, key);
 
    while (HeapTupleIsValid(tup = systable_getnext(scan)))
    {
        Form_pg_depend depform = (Form_pg_depend) GETSTRUCT(tup);
 
        if (depform->refclassid == refclassId && depform->deptype == deptype)
        {
            CatalogTupleDelete(depRel, &tup->t_self);
            count++;
        }
    }
 
    systable_endscan(scan);
 
    table_close(depRel, RowExclusiveLock);
 
    return count;
}
 
/*
 * deleteDependencyRecordsForSpecific -- delete all records with given depender
 * classId/objectId, dependee classId/objectId, of the given deptype.
 * Returns the number of records deleted.
 */
long
deleteDependencyRecordsForSpecific(Oid classId, Oid objectId, char deptype,
                                   Oid refclassId, Oid refobjectId)
{
    long        count = 0;
    Relation    depRel;
    ScanKeyData key[2];
    SysScanDesc scan;
    HeapTuple   tup;
 
    depRel = table_open(DependRelationId, RowExclusiveLock);
 
    ScanKeyInit(&key[0],
                Anum_pg_depend_classid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(classId));
    ScanKeyInit(&key[1],
                Anum_pg_depend_objid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(objectId));
 
    scan = systable_beginscan(depRel, DependDependerIndexId, true,
                              NULL, 2, key);
 
    while (HeapTupleIsValid(tup = systable_getnext(scan)))
    {
        Form_pg_depend depform = (Form_pg_depend) GETSTRUCT(tup);
 
        if (depform->refclassid == refclassId &&
            depform->refobjid == refobjectId &&
            depform->deptype == deptype)
        {
            CatalogTupleDelete(depRel, &tup->t_self);
            count++;
        }
    }
 
    systable_endscan(scan);
 
    table_close(depRel, RowExclusiveLock);
 
    return count;
}
 
/*
 * Adjust dependency record(s) to point to a different object of the same type
 *
 * classId/objectId specify the referencing object.
 * refClassId/oldRefObjectId specify the old referenced object.
 * newRefObjectId is the new referenced object (must be of class refClassId).
 *
 * Note the lack of objsubid parameters.  If there are subobject references
 * they will all be readjusted.  Also, there is an expectation that we are
 * dealing with NORMAL dependencies: if we have to replace an (implicit)
 * dependency on a pinned object with an explicit dependency on an unpinned
 * one, the new one will be NORMAL.
 *
 * Returns the number of records updated -- zero indicates a problem.
 */
long
changeDependencyFor(Oid classId, Oid objectId,
                    Oid refClassId, Oid oldRefObjectId,
                    Oid newRefObjectId)
{
    long        count = 0;
    Relation    depRel;
    ScanKeyData key[2];
    SysScanDesc scan;
    HeapTuple   tup;
    ObjectAddress objAddr;
    ObjectAddress depAddr;
    bool        oldIsPinned;
    bool        newIsPinned;
 
    /*
     * Check to see if either oldRefObjectId or newRefObjectId is pinned.
     * Pinned objects should not have any dependency entries pointing to them,
     * so in these cases we should add or remove a pg_depend entry, or do
     * nothing at all, rather than update an entry as in the normal case.
     */
    objAddr.classId = refClassId;
    objAddr.objectId = oldRefObjectId;
    objAddr.objectSubId = 0;
 
    oldIsPinned = isObjectPinned(&objAddr);
 
    objAddr.objectId = newRefObjectId;
 
    newIsPinned = isObjectPinned(&objAddr);
 
    if (oldIsPinned)
    {
        /*
         * If both are pinned, we need do nothing.  However, return 1 not 0,
         * else callers will think this is an error case.
         */
        if (newIsPinned)
            return 1;
 
        /*
         * There is no old dependency record, but we should insert a new one.
         * Assume a normal dependency is wanted.
         */
        depAddr.classId = classId;
        depAddr.objectId = objectId;
        depAddr.objectSubId = 0;
        recordDependencyOn(&depAddr, &objAddr, DEPENDENCY_NORMAL);
 
        return 1;
    }
 
    depRel = table_open(DependRelationId, RowExclusiveLock);
 
    /* There should be existing dependency record(s), so search. */
    ScanKeyInit(&key[0],
                Anum_pg_depend_classid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(classId));
    ScanKeyInit(&key[1],
                Anum_pg_depend_objid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(objectId));
 
    scan = systable_beginscan(depRel, DependDependerIndexId, true,
                              NULL, 2, key);
 
    while (HeapTupleIsValid((tup = systable_getnext(scan))))
    {
        Form_pg_depend depform = (Form_pg_depend) GETSTRUCT(tup);
 
        if (depform->refclassid == refClassId &&
            depform->refobjid == oldRefObjectId)
        {
            if (newIsPinned)
                CatalogTupleDelete(depRel, &tup->t_self);
            else
            {
                /* make a modifiable copy */
                tup = heap_copytuple(tup);
                depform = (Form_pg_depend) GETSTRUCT(tup);
 
                depform->refobjid = newRefObjectId;
 
                CatalogTupleUpdate(depRel, &tup->t_self, tup);
 
                heap_freetuple(tup);
            }
 
            count++;
        }
    }
 
    systable_endscan(scan);
 
    table_close(depRel, RowExclusiveLock);
 
    return count;
}
 
/*
 * Adjust all dependency records to come from a different object of the same type
 *
 * classId/oldObjectId specify the old referencing object.
 * newObjectId is the new referencing object (must be of class classId).
 *
 * Returns the number of records updated.
 */
long
changeDependenciesOf(Oid classId, Oid oldObjectId,
                     Oid newObjectId)
{
    long        count = 0;
    Relation    depRel;
    ScanKeyData key[2];
    SysScanDesc scan;
    HeapTuple   tup;
 
    depRel = table_open(DependRelationId, RowExclusiveLock);
 
    ScanKeyInit(&key[0],
                Anum_pg_depend_classid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(classId));
    ScanKeyInit(&key[1],
                Anum_pg_depend_objid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(oldObjectId));
 
    scan = systable_beginscan(depRel, DependDependerIndexId, true,
                              NULL, 2, key);
 
    while (HeapTupleIsValid((tup = systable_getnext(scan))))
    {
        Form_pg_depend depform;
 
        /* make a modifiable copy */
        tup = heap_copytuple(tup);
        depform = (Form_pg_depend) GETSTRUCT(tup);
 
        depform->objid = newObjectId;
 
        CatalogTupleUpdate(depRel, &tup->t_self, tup);
 
        heap_freetuple(tup);
 
        count++;
    }
 
    systable_endscan(scan);
 
    table_close(depRel, RowExclusiveLock);
 
    return count;
}
 
/*
 * Adjust all dependency records to point to a different object of the same type
 *
 * refClassId/oldRefObjectId specify the old referenced object.
 * newRefObjectId is the new referenced object (must be of class refClassId).
 *
 * Returns the number of records updated.
 */
long
changeDependenciesOn(Oid refClassId, Oid oldRefObjectId,
                     Oid newRefObjectId)
{
    long        count = 0;
    Relation    depRel;
    ScanKeyData key[2];
    SysScanDesc scan;
    HeapTuple   tup;
    ObjectAddress objAddr;
    bool        newIsPinned;
 
    depRel = table_open(DependRelationId, RowExclusiveLock);
 
    /*
     * If oldRefObjectId is pinned, there won't be any dependency entries on
     * it --- we can't cope in that case.  (This isn't really worth expending
     * code to fix, in current usage; it just means you can't rename stuff out
     * of pg_catalog, which would likely be a bad move anyway.)
     */
    objAddr.classId = refClassId;
    objAddr.objectId = oldRefObjectId;
    objAddr.objectSubId = 0;
 
    if (isObjectPinned(&objAddr))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot remove dependency on %s because it is a system object",
                        getObjectDescription(&objAddr, false))));
 
    /*
     * We can handle adding a dependency on something pinned, though, since
     * that just means deleting the dependency entry.
     */
    objAddr.objectId = newRefObjectId;
 
    newIsPinned = isObjectPinned(&objAddr);
 
    /* Now search for dependency records */
    ScanKeyInit(&key[0],
                Anum_pg_depend_refclassid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(refClassId));
    ScanKeyInit(&key[1],
                Anum_pg_depend_refobjid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(oldRefObjectId));
 
    scan = systable_beginscan(depRel, DependReferenceIndexId, true,
                              NULL, 2, key);
 
    while (HeapTupleIsValid((tup = systable_getnext(scan))))
    {
        if (newIsPinned)
            CatalogTupleDelete(depRel, &tup->t_self);
        else
        {
            Form_pg_depend depform;
 
            /* make a modifiable copy */
            tup = heap_copytuple(tup);
            depform = (Form_pg_depend) GETSTRUCT(tup);
 
            depform->refobjid = newRefObjectId;
 
            CatalogTupleUpdate(depRel, &tup->t_self, tup);
 
            heap_freetuple(tup);
        }
 
        count++;
    }
 
    systable_endscan(scan);
 
    table_close(depRel, RowExclusiveLock);
 
    return count;
}
 
/*
 * isObjectPinned()
 *
 * Test if an object is required for basic database functionality.
 *
 * The passed subId, if any, is ignored; we assume that only whole objects
 * are pinned (and that this implies pinning their components).
 */
static bool
isObjectPinned(const ObjectAddress *object)
{
    return IsPinnedObject(object->classId, object->objectId);
}
 
 
/*
 * Various special-purpose lookups and manipulations of pg_depend.
 */
 
 
/*
 * Find the extension containing the specified object, if any
 *
 * Returns the OID of the extension, or InvalidOid if the object does not
 * belong to any extension.
 *
 * Extension membership is marked by an EXTENSION dependency from the object
 * to the extension.  Note that the result will be indeterminate if pg_depend
 * contains links from this object to more than one extension ... but that
 * should never happen.
 */
Oid
getExtensionOfObject(Oid classId, Oid objectId)
{
    Oid         result = InvalidOid;
    Relation    depRel;
    ScanKeyData key[2];
    SysScanDesc scan;
    HeapTuple   tup;
 
    depRel = table_open(DependRelationId, AccessShareLock);
 
    ScanKeyInit(&key[0],
                Anum_pg_depend_classid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(classId));
    ScanKeyInit(&key[1],
                Anum_pg_depend_objid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(objectId));
 
    scan = systable_beginscan(depRel, DependDependerIndexId, true,
                              NULL, 2, key);
 
    while (HeapTupleIsValid((tup = systable_getnext(scan))))
    {
        Form_pg_depend depform = (Form_pg_depend) GETSTRUCT(tup);
 
        if (depform->refclassid == ExtensionRelationId &&
            depform->deptype == DEPENDENCY_EXTENSION)
        {
            result = depform->refobjid;
            break;              /* no need to keep scanning */
        }
    }
 
    systable_endscan(scan);
 
    table_close(depRel, AccessShareLock);
 
    return result;
}
 
/*
 * Return (possibly NIL) list of extensions that the given object depends on
 * in DEPENDENCY_AUTO_EXTENSION mode.
 */
List *
getAutoExtensionsOfObject(Oid classId, Oid objectId)
{
    List       *result = NIL;
    Relation    depRel;
    ScanKeyData key[2];
    SysScanDesc scan;
    HeapTuple   tup;
 
    depRel = table_open(DependRelationId, AccessShareLock);
 
    ScanKeyInit(&key[0],
                Anum_pg_depend_classid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(classId));
    ScanKeyInit(&key[1],
                Anum_pg_depend_objid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(objectId));
 
    scan = systable_beginscan(depRel, DependDependerIndexId, true,
                              NULL, 2, key);
 
    while (HeapTupleIsValid((tup = systable_getnext(scan))))
    {
        Form_pg_depend depform = (Form_pg_depend) GETSTRUCT(tup);
 
        if (depform->refclassid == ExtensionRelationId &&
            depform->deptype == DEPENDENCY_AUTO_EXTENSION)
            result = lappend_oid(result, depform->refobjid);
    }
 
    systable_endscan(scan);
 
    table_close(depRel, AccessShareLock);
 
    return result;
}
 
/*
 * Detect whether a sequence is marked as "owned" by a column
 *
 * An ownership marker is an AUTO or INTERNAL dependency from the sequence to the
 * column.  If we find one, store the identity of the owning column
 * into *tableId and *colId and return true; else return false.
 *
 * Note: if there's more than one such pg_depend entry then you get
 * a random one of them returned into the out parameters.  This should
 * not happen, though.
 */
bool
sequenceIsOwned(Oid seqId, char deptype, Oid *tableId, int32 *colId)
{
    bool        ret = false;
    Relation    depRel;
    ScanKeyData key[2];
    SysScanDesc scan;
    HeapTuple   tup;
 
    depRel = table_open(DependRelationId, AccessShareLock);
 
    ScanKeyInit(&key[0],
                Anum_pg_depend_classid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(RelationRelationId));
    ScanKeyInit(&key[1],
                Anum_pg_depend_objid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(seqId));
 
    scan = systable_beginscan(depRel, DependDependerIndexId, true,
                              NULL, 2, key);
 
    while (HeapTupleIsValid((tup = systable_getnext(scan))))
    {
        Form_pg_depend depform = (Form_pg_depend) GETSTRUCT(tup);
 
        if (depform->refclassid == RelationRelationId &&
            depform->deptype == deptype)
        {
            *tableId = depform->refobjid;
            *colId = depform->refobjsubid;
            ret = true;
            break;              /* no need to keep scanning */
        }
    }
 
    systable_endscan(scan);
 
    table_close(depRel, AccessShareLock);
 
    return ret;
}
 
/*
 * Collect a list of OIDs of all sequences owned by the specified relation,
 * and column if specified.  If deptype is not zero, then only find sequences
 * with the specified dependency type.
 */
static List *
getOwnedSequences_internal(Oid relid, AttrNumber attnum, char deptype)
{
    List       *result = NIL;
    Relation    depRel;
    ScanKeyData key[3];
    SysScanDesc scan;
    HeapTuple   tup;
 
    depRel = table_open(DependRelationId, AccessShareLock);
 
    ScanKeyInit(&key[0],
                Anum_pg_depend_refclassid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(RelationRelationId));
    ScanKeyInit(&key[1],
                Anum_pg_depend_refobjid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(relid));
    if (attnum)
        ScanKeyInit(&key[2],
                    Anum_pg_depend_refobjsubid,
                    BTEqualStrategyNumber, F_INT4EQ,
                    Int32GetDatum(attnum));
 
    scan = systable_beginscan(depRel, DependReferenceIndexId, true,
                              NULL, attnum ? 3 : 2, key);
 
    while (HeapTupleIsValid(tup = systable_getnext(scan)))
    {
        Form_pg_depend deprec = (Form_pg_depend) GETSTRUCT(tup);
 
        /*
         * We assume any auto or internal dependency of a sequence on a column
         * must be what we are looking for.  (We need the relkind test because
         * indexes can also have auto dependencies on columns.)
         */
        if (deprec->classid == RelationRelationId &&
            deprec->objsubid == 0 &&
            deprec->refobjsubid != 0 &&
            (deprec->deptype == DEPENDENCY_AUTO || deprec->deptype == DEPENDENCY_INTERNAL) &&
            get_rel_relkind(deprec->objid) == RELKIND_SEQUENCE)
        {
            if (!deptype || deprec->deptype == deptype)
                result = lappend_oid(result, deprec->objid);
        }
    }
 
    systable_endscan(scan);
 
    table_close(depRel, AccessShareLock);
 
    return result;
}
 
/*
 * Collect a list of OIDs of all sequences owned (identity or serial) by the
 * specified relation.
 */
List *
getOwnedSequences(Oid relid)
{
    return getOwnedSequences_internal(relid, 0, 0);
}
 
/*
 * Get owned identity sequence, error if not exactly one.
 */
Oid
getIdentitySequence(Oid relid, AttrNumber attnum, bool missing_ok)
{
    List       *seqlist = getOwnedSequences_internal(relid, attnum, DEPENDENCY_INTERNAL);
 
    if (list_length(seqlist) > 1)
        elog(ERROR, "more than one owned sequence found");
    else if (seqlist == NIL)
    {
        if (missing_ok)
            return InvalidOid;
        else
            elog(ERROR, "no owned sequence found");
    }
 
    return linitial_oid(seqlist);
}
 
/*
 * get_index_constraint
 *      Given the OID of an index, return the OID of the owning unique,
 *      primary-key, or exclusion constraint, or InvalidOid if there
 *      is no owning constraint.
 */
Oid
get_index_constraint(Oid indexId)
{
    Oid         constraintId = InvalidOid;
    Relation    depRel;
    ScanKeyData key[3];
    SysScanDesc scan;
    HeapTuple   tup;
 
    /* Search the dependency table for the index */
    depRel = table_open(DependRelationId, AccessShareLock);
 
    ScanKeyInit(&key[0],
                Anum_pg_depend_classid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(RelationRelationId));
    ScanKeyInit(&key[1],
                Anum_pg_depend_objid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(indexId));
    ScanKeyInit(&key[2],
                Anum_pg_depend_objsubid,
                BTEqualStrategyNumber, F_INT4EQ,
                Int32GetDatum(0));
 
    scan = systable_beginscan(depRel, DependDependerIndexId, true,
                              NULL, 3, key);
 
    while (HeapTupleIsValid(tup = systable_getnext(scan)))
    {
        Form_pg_depend deprec = (Form_pg_depend) GETSTRUCT(tup);
 
        /*
         * We assume any internal dependency on a constraint must be what we
         * are looking for.
         */
        if (deprec->refclassid == ConstraintRelationId &&
            deprec->refobjsubid == 0 &&
            deprec->deptype == DEPENDENCY_INTERNAL)
        {
            constraintId = deprec->refobjid;
            break;
        }
    }
 
    systable_endscan(scan);
    table_close(depRel, AccessShareLock);
 
    return constraintId;
}
 
/*
 * get_index_ref_constraints
 *      Given the OID of an index, return the OID of all foreign key
 *      constraints which reference the index.
 */
List *
get_index_ref_constraints(Oid indexId)
{
    List       *result = NIL;
    Relation    depRel;
    ScanKeyData key[3];
    SysScanDesc scan;
    HeapTuple   tup;
 
    /* Search the dependency table for the index */
    depRel = table_open(DependRelationId, AccessShareLock);
 
    ScanKeyInit(&key[0],
                Anum_pg_depend_refclassid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(RelationRelationId));
    ScanKeyInit(&key[1],
                Anum_pg_depend_refobjid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(indexId));
    ScanKeyInit(&key[2],
                Anum_pg_depend_refobjsubid,
                BTEqualStrategyNumber, F_INT4EQ,
                Int32GetDatum(0));
 
    scan = systable_beginscan(depRel, DependReferenceIndexId, true,
                              NULL, 3, key);
 
    while (HeapTupleIsValid(tup = systable_getnext(scan)))
    {
        Form_pg_depend deprec = (Form_pg_depend) GETSTRUCT(tup);
 
        /*
         * We assume any normal dependency from a constraint must be what we
         * are looking for.
         */
        if (deprec->classid == ConstraintRelationId &&
            deprec->objsubid == 0 &&
            deprec->deptype == DEPENDENCY_NORMAL)
        {
            result = lappend_oid(result, deprec->objid);
        }
    }
 
    systable_endscan(scan);
    table_close(depRel, AccessShareLock);
 
    return result;
}