pg_depend.c

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/*-------------------------------------------------------------------------
 *
 * pg_depend.c
 *    routines to support manipulation of the pg_depend relation
 *
 * Portions Copyright (c) 1996-2020, 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/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, Relation rel);


/*
 * 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;
    HeapTuple   tup;
    int         i;
    bool        nulls[Natts_pg_depend];
    Datum       values[Natts_pg_depend];

    if (nreferenced <= 0)
        return;                 /* nothing to do */

    /*
     * During bootstrap, do nothing since pg_depend may not exist yet. initdb
     * will fill in appropriate pg_depend entries after bootstrap.
     */
    if (IsBootstrapProcessingMode())
        return;

    dependDesc = table_open(DependRelationId, RowExclusiveLock);

    /* Don't open indexes unless we need to make an update */
    indstate = NULL;

    memset(nulls, false, sizeof(nulls));

    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, dependDesc))
        {
            /*
             * Record the Dependency.  Note we don't bother to check for
             * duplicate dependencies; there's no harm in them.
             */
            values[Anum_pg_depend_classid - 1] = ObjectIdGetDatum(depender->classId);
            values[Anum_pg_depend_objid - 1] = ObjectIdGetDatum(depender->objectId);
            values[Anum_pg_depend_objsubid - 1] = Int32GetDatum(depender->objectSubId);

            values[Anum_pg_depend_refclassid - 1] = ObjectIdGetDatum(referenced->classId);
            values[Anum_pg_depend_refobjid - 1] = ObjectIdGetDatum(referenced->objectId);
            values[Anum_pg_depend_refobjsubid - 1] = Int32GetDatum(referenced->objectSubId);

            values[Anum_pg_depend_deptype - 1] = CharGetDatum((char) behavior);

            tup = heap_form_tuple(dependDesc->rd_att, values, nulls);

            /* fetch index info only when we know we need it */
            if (indstate == NULL)
                indstate = CatalogOpenIndexes(dependDesc);

            CatalogTupleInsertWithInfo(dependDesc, tup, indstate);

            heap_freetuple(tup);
        }
    }

    if (indstate != NULL)
        CatalogCloseIndexes(indstate);

    table_close(dependDesc, RowExclusiveLock);
}

/*
 * If we are executing a CREATE EXTENSION operation, mark the given object
 * as being a member of the extension.  Otherwise, do nothing.
 *
 * This must be called during creation of any user-definable object type
 * that could be a member of an extension.
 *
 * If isReplace is true, the object already existed (or might have already
 * existed), so we must check for a pre-existing extension membership entry.
 * Passing false is a guarantee that the object is newly created, and so
 * could not already be a member of any extension.
 */
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;

            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),
                                get_extension_name(oldext))));
            }
        }

        /* OK, record it as a member of CurrentExtensionObject */
        extension.classId = ExtensionRelationId;
        extension.objectId = CurrentExtensionObject;
        extension.objectSubId = 0;

        recordDependencyOn(object, &extension, DEPENDENCY_EXTENSION);
    }
}

/*
 * 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;
}

/*
 * 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;

    depRel = table_open(DependRelationId, RowExclusiveLock);

    /*
     * 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, depRel);

    objAddr.objectId = newRefObjectId;

    newIsPinned = isObjectPinned(&objAddr, depRel);

    if (oldIsPinned)
    {
        table_close(depRel, RowExclusiveLock);

        /*
         * 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;
    }

    /* 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 = (Form_pg_depend) GETSTRUCT(tup);

        /* 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, depRel))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot remove dependency on %s because it is a system object",
                        getObjectDescription(&objAddr))));

    /*
     * We can handle adding a dependency on something pinned, though, since
     * that just means deleting the dependency entry.
     */
    objAddr.objectId = newRefObjectId;

    newIsPinned = isObjectPinned(&objAddr, depRel);

    /* 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))))
    {
        Form_pg_depend depform = (Form_pg_depend) GETSTRUCT(tup);

        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;
}

/*
 * isObjectPinned()
 *
 * Test if an object is required for basic database functionality.
 * Caller must already have opened pg_depend.
 *
 * 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, Relation rel)
{
    bool        ret = false;
    SysScanDesc scan;
    HeapTuple   tup;
    ScanKeyData key[2];

    ScanKeyInit(&key[0],
                Anum_pg_depend_refclassid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(object->classId));

    ScanKeyInit(&key[1],
                Anum_pg_depend_refobjid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(object->objectId));

    scan = systable_beginscan(rel, DependReferenceIndexId, true,
                              NULL, 2, key);

    /*
     * Since we won't generate additional pg_depend entries for pinned
     * objects, there can be at most one entry referencing a pinned object.
     * Hence, it's sufficient to look at the first returned tuple; we don't
     * need to loop.
     */
    tup = systable_getnext(scan);
    if (HeapTupleIsValid(tup))
    {
        Form_pg_depend foundDep = (Form_pg_depend) GETSTRUCT(tup);

        if (foundDep->deptype == DEPENDENCY_PIN)
            ret = true;
    }

    systable_endscan(scan);

    return ret;
}


/*
 * 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;
}

/*
 * 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 (list_length(seqlist) < 1)
    {
        if (missing_ok)
            return InvalidOid;
        else
            elog(ERROR, "no owned sequence found");
    }

    return linitial_oid(seqlist);
}

/*
 * get_constraint_index
 *      Given the OID of a unique, primary-key, or exclusion constraint,
 *      return the OID of the underlying index.
 *
 * Return InvalidOid if the index couldn't be found; this suggests the
 * given OID is bogus, but we leave it to caller to decide what to do.
 */
Oid
get_constraint_index(Oid constraintId)
{
    Oid         indexId = InvalidOid;
    Relation    depRel;
    ScanKeyData key[3];
    SysScanDesc scan;
    HeapTuple   tup;

    /* Search the dependency table for the dependent index */
    depRel = table_open(DependRelationId, AccessShareLock);

    ScanKeyInit(&key[0],
                Anum_pg_depend_refclassid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(ConstraintRelationId));
    ScanKeyInit(&key[1],
                Anum_pg_depend_refobjid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(constraintId));
    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 internal dependency of an index on the constraint
         * must be what we are looking for.
         */
        if (deprec->classid == RelationRelationId &&
            deprec->objsubid == 0 &&
            deprec->deptype == DEPENDENCY_INTERNAL)
        {
            char        relkind = get_rel_relkind(deprec->objid);

            /*
             * This is pure paranoia; there shouldn't be any other relkinds
             * dependent on a constraint.
             */
            if (relkind != RELKIND_INDEX &&
                relkind != RELKIND_PARTITIONED_INDEX)
                continue;

            indexId = deprec->objid;
            break;
        }
    }

    systable_endscan(scan);
    table_close(depRel, AccessShareLock);

    return indexId;
}

/*
 * 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;
}