dependency.c

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/*-------------------------------------------------------------------------
 *
 * dependency.c
 *    Routines to support inter-object dependencies.
 *
 *
 * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/backend/catalog/dependency.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/htup_details.h"
#include "access/xact.h"
#include "catalog/dependency.h"
#include "catalog/heap.h"
#include "catalog/index.h"
#include "catalog/objectaccess.h"
#include "catalog/pg_am.h"
#include "catalog/pg_amop.h"
#include "catalog/pg_amproc.h"
#include "catalog/pg_attrdef.h"
#include "catalog/pg_authid.h"
#include "catalog/pg_cast.h"
#include "catalog/pg_collation.h"
#include "catalog/pg_constraint.h"
#include "catalog/pg_conversion.h"
#include "catalog/pg_database.h"
#include "catalog/pg_default_acl.h"
#include "catalog/pg_depend.h"
#include "catalog/pg_event_trigger.h"
#include "catalog/pg_extension.h"
#include "catalog/pg_foreign_data_wrapper.h"
#include "catalog/pg_foreign_server.h"
#include "catalog/pg_init_privs.h"
#include "catalog/pg_language.h"
#include "catalog/pg_largeobject.h"
#include "catalog/pg_namespace.h"
#include "catalog/pg_opclass.h"
#include "catalog/pg_operator.h"
#include "catalog/pg_opfamily.h"
#include "catalog/pg_policy.h"
#include "catalog/pg_proc.h"
#include "catalog/pg_publication.h"
#include "catalog/pg_publication_rel.h"
#include "catalog/pg_rewrite.h"
#include "catalog/pg_statistic_ext.h"
#include "catalog/pg_subscription.h"
#include "catalog/pg_tablespace.h"
#include "catalog/pg_transform.h"
#include "catalog/pg_trigger.h"
#include "catalog/pg_ts_config.h"
#include "catalog/pg_ts_dict.h"
#include "catalog/pg_ts_parser.h"
#include "catalog/pg_ts_template.h"
#include "catalog/pg_type.h"
#include "catalog/pg_user_mapping.h"
#include "commands/comment.h"
#include "commands/defrem.h"
#include "commands/event_trigger.h"
#include "commands/extension.h"
#include "commands/policy.h"
#include "commands/proclang.h"
#include "commands/publicationcmds.h"
#include "commands/schemacmds.h"
#include "commands/seclabel.h"
#include "commands/sequence.h"
#include "commands/trigger.h"
#include "commands/typecmds.h"
#include "nodes/nodeFuncs.h"
#include "parser/parsetree.h"
#include "rewrite/rewriteRemove.h"
#include "storage/lmgr.h"
#include "utils/fmgroids.h"
#include "utils/guc.h"
#include "utils/lsyscache.h"
#include "utils/syscache.h"
#include "utils/tqual.h"


/*
 * Deletion processing requires additional state for each ObjectAddress that
 * it's planning to delete.  For simplicity and code-sharing we make the
 * ObjectAddresses code support arrays with or without this extra state.
 */
typedef struct
{
    int         flags;          /* bitmask, see bit definitions below */
    ObjectAddress dependee;     /* object whose deletion forced this one */
} ObjectAddressExtra;

/* ObjectAddressExtra flag bits */
#define DEPFLAG_ORIGINAL    0x0001  /* an original deletion target */
#define DEPFLAG_NORMAL      0x0002  /* reached via normal dependency */
#define DEPFLAG_AUTO        0x0004  /* reached via auto dependency */
#define DEPFLAG_INTERNAL    0x0008  /* reached via internal dependency */
#define DEPFLAG_EXTENSION   0x0010  /* reached via extension dependency */
#define DEPFLAG_REVERSE     0x0020  /* reverse internal/extension link */


/* expansible list of ObjectAddresses */
struct ObjectAddresses
{
    ObjectAddress *refs;        /* => palloc'd array */
    ObjectAddressExtra *extras; /* => palloc'd array, or NULL if not used */
    int         numrefs;        /* current number of references */
    int         maxrefs;        /* current size of palloc'd array(s) */
};

/* typedef ObjectAddresses appears in dependency.h */

/* threaded list of ObjectAddresses, for recursion detection */
typedef struct ObjectAddressStack
{
    const ObjectAddress *object;    /* object being visited */
    int         flags;          /* its current flag bits */
    struct ObjectAddressStack *next;    /* next outer stack level */
} ObjectAddressStack;

/* for find_expr_references_walker */
typedef struct
{
    ObjectAddresses *addrs;     /* addresses being accumulated */
    List       *rtables;        /* list of rangetables to resolve Vars */
} find_expr_references_context;

/*
 * This constant table maps ObjectClasses to the corresponding catalog OIDs.
 * See also getObjectClass().
 */
static const Oid object_classes[] = {
    RelationRelationId,         /* OCLASS_CLASS */
    ProcedureRelationId,        /* OCLASS_PROC */
    TypeRelationId,             /* OCLASS_TYPE */
    CastRelationId,             /* OCLASS_CAST */
    CollationRelationId,        /* OCLASS_COLLATION */
    ConstraintRelationId,       /* OCLASS_CONSTRAINT */
    ConversionRelationId,       /* OCLASS_CONVERSION */
    AttrDefaultRelationId,      /* OCLASS_DEFAULT */
    LanguageRelationId,         /* OCLASS_LANGUAGE */
    LargeObjectRelationId,      /* OCLASS_LARGEOBJECT */
    OperatorRelationId,         /* OCLASS_OPERATOR */
    OperatorClassRelationId,    /* OCLASS_OPCLASS */
    OperatorFamilyRelationId,   /* OCLASS_OPFAMILY */
    AccessMethodRelationId,     /* OCLASS_AM */
    AccessMethodOperatorRelationId, /* OCLASS_AMOP */
    AccessMethodProcedureRelationId,    /* OCLASS_AMPROC */
    RewriteRelationId,          /* OCLASS_REWRITE */
    TriggerRelationId,          /* OCLASS_TRIGGER */
    NamespaceRelationId,        /* OCLASS_SCHEMA */
    StatisticExtRelationId,     /* OCLASS_STATISTIC_EXT */
    TSParserRelationId,         /* OCLASS_TSPARSER */
    TSDictionaryRelationId,     /* OCLASS_TSDICT */
    TSTemplateRelationId,       /* OCLASS_TSTEMPLATE */
    TSConfigRelationId,         /* OCLASS_TSCONFIG */
    AuthIdRelationId,           /* OCLASS_ROLE */
    DatabaseRelationId,         /* OCLASS_DATABASE */
    TableSpaceRelationId,       /* OCLASS_TBLSPACE */
    ForeignDataWrapperRelationId,   /* OCLASS_FDW */
    ForeignServerRelationId,    /* OCLASS_FOREIGN_SERVER */
    UserMappingRelationId,      /* OCLASS_USER_MAPPING */
    DefaultAclRelationId,       /* OCLASS_DEFACL */
    ExtensionRelationId,        /* OCLASS_EXTENSION */
    EventTriggerRelationId,     /* OCLASS_EVENT_TRIGGER */
    PolicyRelationId,           /* OCLASS_POLICY */
    PublicationRelationId,      /* OCLASS_PUBLICATION */
    PublicationRelRelationId,   /* OCLASS_PUBLICATION_REL */
    SubscriptionRelationId,     /* OCLASS_SUBSCRIPTION */
    TransformRelationId         /* OCLASS_TRANSFORM */
};


static void findDependentObjects(const ObjectAddress *object,
                     int objflags,
                     int flags,
                     ObjectAddressStack *stack,
                     ObjectAddresses *targetObjects,
                     const ObjectAddresses *pendingObjects,
                     Relation *depRel);
static void reportDependentObjects(const ObjectAddresses *targetObjects,
                       DropBehavior behavior,
                       int flags,
                       const ObjectAddress *origObject);
static void deleteOneObject(const ObjectAddress *object,
                Relation *depRel, int32 flags);
static void doDeletion(const ObjectAddress *object, int flags);
static void AcquireDeletionLock(const ObjectAddress *object, int flags);
static void ReleaseDeletionLock(const ObjectAddress *object);
static bool find_expr_references_walker(Node *node,
                            find_expr_references_context *context);
static void eliminate_duplicate_dependencies(ObjectAddresses *addrs);
static int  object_address_comparator(const void *a, const void *b);
static void add_object_address(ObjectClass oclass, Oid objectId, int32 subId,
                   ObjectAddresses *addrs);
static void add_exact_object_address_extra(const ObjectAddress *object,
                               const ObjectAddressExtra *extra,
                               ObjectAddresses *addrs);
static bool object_address_present_add_flags(const ObjectAddress *object,
                                 int flags,
                                 ObjectAddresses *addrs);
static bool stack_address_present_add_flags(const ObjectAddress *object,
                                int flags,
                                ObjectAddressStack *stack);
static void DeleteInitPrivs(const ObjectAddress *object);


/*
 * Go through the objects given running the final actions on them, and execute
 * the actual deletion.
 */
static void
deleteObjectsInList(ObjectAddresses *targetObjects, Relation *depRel,
                    int flags)
{
    int         i;

    /*
     * Keep track of objects for event triggers, if necessary.
     */
    if (trackDroppedObjectsNeeded() && !(flags & PERFORM_DELETION_INTERNAL))
    {
        for (i = 0; i < targetObjects->numrefs; i++)
        {
            const ObjectAddress *thisobj = &targetObjects->refs[i];
            const ObjectAddressExtra *extra = &targetObjects->extras[i];
            bool        original = false;
            bool        normal = false;

            if (extra->flags & DEPFLAG_ORIGINAL)
                original = true;
            if (extra->flags & DEPFLAG_NORMAL)
                normal = true;
            if (extra->flags & DEPFLAG_REVERSE)
                normal = true;

            if (EventTriggerSupportsObjectClass(getObjectClass(thisobj)))
            {
                EventTriggerSQLDropAddObject(thisobj, original, normal);
            }
        }
    }

    /*
     * Delete all the objects in the proper order, except that if told to, we
     * should skip the original object(s).
     */
    for (i = 0; i < targetObjects->numrefs; i++)
    {
        ObjectAddress *thisobj = targetObjects->refs + i;
        ObjectAddressExtra *thisextra = targetObjects->extras + i;

        if ((flags & PERFORM_DELETION_SKIP_ORIGINAL) &&
            (thisextra->flags & DEPFLAG_ORIGINAL))
            continue;

        deleteOneObject(thisobj, depRel, flags);
    }
}

/*
 * performDeletion: attempt to drop the specified object.  If CASCADE
 * behavior is specified, also drop any dependent objects (recursively).
 * If RESTRICT behavior is specified, error out if there are any dependent
 * objects, except for those that should be implicitly dropped anyway
 * according to the dependency type.
 *
 * This is the outer control routine for all forms of DROP that drop objects
 * that can participate in dependencies.  Note that performMultipleDeletions
 * is a variant on the same theme; if you change anything here you'll likely
 * need to fix that too.
 *
 * Bits in the flags argument can include:
 *
 * PERFORM_DELETION_INTERNAL: indicates that the drop operation is not the
 * direct result of a user-initiated action.  For example, when a temporary
 * schema is cleaned out so that a new backend can use it, or when a column
 * default is dropped as an intermediate step while adding a new one, that's
 * an internal operation.  On the other hand, when we drop something because
 * the user issued a DROP statement against it, that's not internal. Currently
 * this suppresses calling event triggers and making some permissions checks.
 *
 * PERFORM_DELETION_CONCURRENTLY: perform the drop concurrently.  This does
 * not currently work for anything except dropping indexes; don't set it for
 * other object types or you may get strange results.
 *
 * PERFORM_DELETION_QUIETLY: reduce message level from NOTICE to DEBUG2.
 *
 * PERFORM_DELETION_SKIP_ORIGINAL: do not delete the specified object(s),
 * but only what depends on it/them.
 *
 * PERFORM_DELETION_SKIP_EXTENSIONS: do not delete extensions, even when
 * deleting objects that are part of an extension.  This should generally
 * be used only when dropping temporary objects.
 */
void
performDeletion(const ObjectAddress *object,
                DropBehavior behavior, int flags)
{
    Relation    depRel;
    ObjectAddresses *targetObjects;

    /*
     * We save some cycles by opening pg_depend just once and passing the
     * Relation pointer down to all the recursive deletion steps.
     */
    depRel = heap_open(DependRelationId, RowExclusiveLock);

    /*
     * Acquire deletion lock on the target object.  (Ideally the caller has
     * done this already, but many places are sloppy about it.)
     */
    AcquireDeletionLock(object, 0);

    /*
     * Construct a list of objects to delete (ie, the given object plus
     * everything directly or indirectly dependent on it).
     */
    targetObjects = new_object_addresses();

    findDependentObjects(object,
                         DEPFLAG_ORIGINAL,
                         flags,
                         NULL,  /* empty stack */
                         targetObjects,
                         NULL,  /* no pendingObjects */
                         &depRel);

    /*
     * Check if deletion is allowed, and report about cascaded deletes.
     */
    reportDependentObjects(targetObjects,
                           behavior,
                           flags,
                           object);

    /* do the deed */
    deleteObjectsInList(targetObjects, &depRel, flags);

    /* And clean up */
    free_object_addresses(targetObjects);

    heap_close(depRel, RowExclusiveLock);
}

/*
 * performMultipleDeletions: Similar to performDeletion, but act on multiple
 * objects at once.
 *
 * The main difference from issuing multiple performDeletion calls is that the
 * list of objects that would be implicitly dropped, for each object to be
 * dropped, is the union of the implicit-object list for all objects.  This
 * makes each check be more relaxed.
 */
void
performMultipleDeletions(const ObjectAddresses *objects,
                         DropBehavior behavior, int flags)
{
    Relation    depRel;
    ObjectAddresses *targetObjects;
    int         i;

    /* No work if no objects... */
    if (objects->numrefs <= 0)
        return;

    /*
     * We save some cycles by opening pg_depend just once and passing the
     * Relation pointer down to all the recursive deletion steps.
     */
    depRel = heap_open(DependRelationId, RowExclusiveLock);

    /*
     * Construct a list of objects to delete (ie, the given objects plus
     * everything directly or indirectly dependent on them).  Note that
     * because we pass the whole objects list as pendingObjects context, we
     * won't get a failure from trying to delete an object that is internally
     * dependent on another one in the list; we'll just skip that object and
     * delete it when we reach its owner.
     */
    targetObjects = new_object_addresses();

    for (i = 0; i < objects->numrefs; i++)
    {
        const ObjectAddress *thisobj = objects->refs + i;

        /*
         * Acquire deletion lock on each target object.  (Ideally the caller
         * has done this already, but many places are sloppy about it.)
         */
        AcquireDeletionLock(thisobj, flags);

        findDependentObjects(thisobj,
                             DEPFLAG_ORIGINAL,
                             flags,
                             NULL,  /* empty stack */
                             targetObjects,
                             objects,
                             &depRel);
    }

    /*
     * Check if deletion is allowed, and report about cascaded deletes.
     *
     * If there's exactly one object being deleted, report it the same way as
     * in performDeletion(), else we have to be vaguer.
     */
    reportDependentObjects(targetObjects,
                           behavior,
                           flags,
                           (objects->numrefs == 1 ? objects->refs : NULL));

    /* do the deed */
    deleteObjectsInList(targetObjects, &depRel, flags);

    /* And clean up */
    free_object_addresses(targetObjects);

    heap_close(depRel, RowExclusiveLock);
}

/*
 * findDependentObjects - find all objects that depend on 'object'
 *
 * For every object that depends on the starting object, acquire a deletion
 * lock on the object, add it to targetObjects (if not already there),
 * and recursively find objects that depend on it.  An object's dependencies
 * will be placed into targetObjects before the object itself; this means
 * that the finished list's order represents a safe deletion order.
 *
 * The caller must already have a deletion lock on 'object' itself,
 * but must not have added it to targetObjects.  (Note: there are corner
 * cases where we won't add the object either, and will also release the
 * caller-taken lock.  This is a bit ugly, but the API is set up this way
 * to allow easy rechecking of an object's liveness after we lock it.  See
 * notes within the function.)
 *
 * When dropping a whole object (subId = 0), we find dependencies for
 * its sub-objects too.
 *
 *  object: the object to add to targetObjects and find dependencies on
 *  objflags: flags to be ORed into the object's targetObjects entry
 *  flags: PERFORM_DELETION_xxx flags for the deletion operation as a whole
 *  stack: list of objects being visited in current recursion; topmost item
 *          is the object that we recursed from (NULL for external callers)
 *  targetObjects: list of objects that are scheduled to be deleted
 *  pendingObjects: list of other objects slated for destruction, but
 *          not necessarily in targetObjects yet (can be NULL if none)
 *  *depRel: already opened pg_depend relation
 *
 * Note: objflags describes the reason for visiting this particular object
 * at this time, and is not passed down when recursing.  The flags argument
 * is passed down, since it describes what we're doing overall.
 */
static void
findDependentObjects(const ObjectAddress *object,
                     int objflags,
                     int flags,
                     ObjectAddressStack *stack,
                     ObjectAddresses *targetObjects,
                     const ObjectAddresses *pendingObjects,
                     Relation *depRel)
{
    ScanKeyData key[3];
    int         nkeys;
    SysScanDesc scan;
    HeapTuple   tup;
    ObjectAddress otherObject;
    ObjectAddressStack mystack;
    ObjectAddressExtra extra;

    /*
     * If the target object is already being visited in an outer recursion
     * level, just report the current objflags back to that level and exit.
     * This is needed to avoid infinite recursion in the face of circular
     * dependencies.
     *
     * The stack check alone would result in dependency loops being broken at
     * an arbitrary point, ie, the first member object of the loop to be
     * visited is the last one to be deleted.  This is obviously unworkable.
     * However, the check for internal dependency below guarantees that we
     * will not break a loop at an internal dependency: if we enter the loop
     * at an "owned" object we will switch and start at the "owning" object
     * instead.  We could probably hack something up to avoid breaking at an
     * auto dependency, too, if we had to.  However there are no known cases
     * where that would be necessary.
     */
    if (stack_address_present_add_flags(object, objflags, stack))
        return;

    /*
     * It's also possible that the target object has already been completely
     * processed and put into targetObjects.  If so, again we just add the
     * specified objflags to its entry and return.
     *
     * (Note: in these early-exit cases we could release the caller-taken
     * lock, since the object is presumably now locked multiple times; but it
     * seems not worth the cycles.)
     */
    if (object_address_present_add_flags(object, objflags, targetObjects))
        return;

    /*
     * The target object might be internally dependent on some other object
     * (its "owner"), and/or be a member of an extension (also considered its
     * owner).  If so, and if we aren't recursing from the owning object, we
     * have to transform this deletion request into a deletion request of the
     * owning object.  (We'll eventually recurse back to this object, but the
     * owning object has to be visited first so it will be deleted after.) The
     * way to find out about this is to scan the pg_depend entries that show
     * what this object depends on.
     */
    ScanKeyInit(&key[0],
                Anum_pg_depend_classid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(object->classId));
    ScanKeyInit(&key[1],
                Anum_pg_depend_objid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(object->objectId));
    if (object->objectSubId != 0)
    {
        ScanKeyInit(&key[2],
                    Anum_pg_depend_objsubid,
                    BTEqualStrategyNumber, F_INT4EQ,
                    Int32GetDatum(object->objectSubId));
        nkeys = 3;
    }
    else
        nkeys = 2;

    scan = systable_beginscan(*depRel, DependDependerIndexId, true,
                              NULL, nkeys, key);

    while (HeapTupleIsValid(tup = systable_getnext(scan)))
    {
        Form_pg_depend foundDep = (Form_pg_depend) GETSTRUCT(tup);

        otherObject.classId = foundDep->refclassid;
        otherObject.objectId = foundDep->refobjid;
        otherObject.objectSubId = foundDep->refobjsubid;

        switch (foundDep->deptype)
        {
            case DEPENDENCY_NORMAL:
            case DEPENDENCY_AUTO:
            case DEPENDENCY_AUTO_EXTENSION:
                /* no problem */
                break;

            case DEPENDENCY_EXTENSION:

                /*
                 * If told to, ignore EXTENSION dependencies altogether.  This
                 * flag is normally used to prevent dropping extensions during
                 * temporary-object cleanup, even if a temp object was created
                 * during an extension script.
                 */
                if (flags & PERFORM_DELETION_SKIP_EXTENSIONS)
                    break;

                /*
                 * If the other object is the extension currently being
                 * created/altered, ignore this dependency and continue with
                 * the deletion.  This allows dropping of an extension's
                 * objects within the extension's scripts, as well as corner
                 * cases such as dropping a transient object created within
                 * such a script.
                 */
                if (creating_extension &&
                    otherObject.classId == ExtensionRelationId &&
                    otherObject.objectId == CurrentExtensionObject)
                    break;

                /* Otherwise, treat this like an internal dependency */
                /* FALL THRU */

            case DEPENDENCY_INTERNAL:
            case DEPENDENCY_INTERNAL_AUTO:

                /*
                 * This object is part of the internal implementation of
                 * another object, or is part of the extension that is the
                 * other object.  We have three cases:
                 *
                 * 1. At the outermost recursion level, disallow the DROP. (We
                 * just ereport here, rather than proceeding, since no other
                 * dependencies are likely to be interesting.)  However, if
                 * the owning object is listed in pendingObjects, just release
                 * the caller's lock and return; we'll eventually complete the
                 * DROP when we reach that entry in the pending list.
                 */
                if (stack == NULL)
                {
                    char       *otherObjDesc;

                    if (pendingObjects &&
                        object_address_present(&otherObject, pendingObjects))
                    {
                        systable_endscan(scan);
                        /* need to release caller's lock; see notes below */
                        ReleaseDeletionLock(object);
                        return;
                    }
                    otherObjDesc = getObjectDescription(&otherObject);
                    ereport(ERROR,
                            (errcode(ERRCODE_DEPENDENT_OBJECTS_STILL_EXIST),
                             errmsg("cannot drop %s because %s requires it",
                                    getObjectDescription(object),
                                    otherObjDesc),
                             errhint("You can drop %s instead.",
                                     otherObjDesc)));
                }

                /*
                 * 2. When recursing from the other end of this dependency,
                 * it's okay to continue with the deletion.  This holds when
                 * recursing from a whole object that includes the nominal
                 * other end as a component, too.  Since there can be more
                 * than one "owning" object, we have to allow matches that are
                 * more than one level down in the stack.
                 */
                if (stack_address_present_add_flags(&otherObject, 0, stack))
                    break;

                /*
                 * 3. Not all the owning objects have been visited, so
                 * transform this deletion request into a delete of this
                 * owning object.
                 *
                 * For INTERNAL_AUTO dependencies, we don't enforce this;
                 * in other words, we don't follow the links back to the
                 * owning object.
                 */
                if (foundDep->deptype == DEPENDENCY_INTERNAL_AUTO)
                    break;

                /*
                 * First, release caller's lock on this object and get
                 * deletion lock on the owning object.  (We must release
                 * caller's lock to avoid deadlock against a concurrent
                 * deletion of the owning object.)
                 */
                ReleaseDeletionLock(object);
                AcquireDeletionLock(&otherObject, 0);

                /*
                 * The owning object might have been deleted while we waited
                 * to lock it; if so, neither it nor the current object are
                 * interesting anymore.  We test this by checking the
                 * pg_depend entry (see notes below).
                 */
                if (!systable_recheck_tuple(scan, tup))
                {
                    systable_endscan(scan);
                    ReleaseDeletionLock(&otherObject);
                    return;
                }

                /*
                 * Okay, recurse to the owning object instead of proceeding.
                 *
                 * We do not need to stack the current object; we want the
                 * traversal order to be as if the original reference had
                 * linked to the owning object instead of this one.
                 *
                 * The dependency type is a "reverse" dependency: we need to
                 * delete the owning object if this one is to be deleted, but
                 * this linkage is never a reason for an automatic deletion.
                 */
                findDependentObjects(&otherObject,
                                     DEPFLAG_REVERSE,
                                     flags,
                                     stack,
                                     targetObjects,
                                     pendingObjects,
                                     depRel);
                /* And we're done here. */
                systable_endscan(scan);
                return;

            case DEPENDENCY_PIN:

                /*
                 * Should not happen; PIN dependencies should have zeroes in
                 * the depender fields...
                 */
                elog(ERROR, "incorrect use of PIN dependency with %s",
                     getObjectDescription(object));
                break;
            default:
                elog(ERROR, "unrecognized dependency type '%c' for %s",
                     foundDep->deptype, getObjectDescription(object));
                break;
        }
    }

    systable_endscan(scan);

    /*
     * Now recurse to any dependent objects.  We must visit them first since
     * they have to be deleted before the current object.
     */
    mystack.object = object;    /* set up a new stack level */
    mystack.flags = objflags;
    mystack.next = stack;

    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));
    if (object->objectSubId != 0)
    {
        ScanKeyInit(&key[2],
                    Anum_pg_depend_refobjsubid,
                    BTEqualStrategyNumber, F_INT4EQ,
                    Int32GetDatum(object->objectSubId));
        nkeys = 3;
    }
    else
        nkeys = 2;

    scan = systable_beginscan(*depRel, DependReferenceIndexId, true,
                              NULL, nkeys, key);

    while (HeapTupleIsValid(tup = systable_getnext(scan)))
    {
        Form_pg_depend foundDep = (Form_pg_depend) GETSTRUCT(tup);
        int         subflags;

        otherObject.classId = foundDep->classid;
        otherObject.objectId = foundDep->objid;
        otherObject.objectSubId = foundDep->objsubid;

        /*
         * Must lock the dependent object before recursing to it.
         */
        AcquireDeletionLock(&otherObject, 0);

        /*
         * The dependent object might have been deleted while we waited to
         * lock it; if so, we don't need to do anything more with it. We can
         * test this cheaply and independently of the object's type by seeing
         * if the pg_depend tuple we are looking at is still live. (If the
         * object got deleted, the tuple would have been deleted too.)
         */
        if (!systable_recheck_tuple(scan, tup))
        {
            /* release the now-useless lock */
            ReleaseDeletionLock(&otherObject);
            /* and continue scanning for dependencies */
            continue;
        }

        /* Recurse, passing objflags indicating the dependency type */
        switch (foundDep->deptype)
        {
            case DEPENDENCY_NORMAL:
                subflags = DEPFLAG_NORMAL;
                break;
            case DEPENDENCY_AUTO:
            case DEPENDENCY_AUTO_EXTENSION:
                subflags = DEPFLAG_AUTO;
                break;
            case DEPENDENCY_INTERNAL_AUTO:
            case DEPENDENCY_INTERNAL:
                subflags = DEPFLAG_INTERNAL;
                break;
            case DEPENDENCY_EXTENSION:
                subflags = DEPFLAG_EXTENSION;
                break;
            case DEPENDENCY_PIN:

                /*
                 * For a PIN dependency we just ereport immediately; there
                 * won't be any others to report.
                 */
                ereport(ERROR,
                        (errcode(ERRCODE_DEPENDENT_OBJECTS_STILL_EXIST),
                         errmsg("cannot drop %s because it is required by the database system",
                                getObjectDescription(object))));
                subflags = 0;   /* keep compiler quiet */
                break;
            default:
                elog(ERROR, "unrecognized dependency type '%c' for %s",
                     foundDep->deptype, getObjectDescription(object));
                subflags = 0;   /* keep compiler quiet */
                break;
        }

        findDependentObjects(&otherObject,
                             subflags,
                             flags,
                             &mystack,
                             targetObjects,
                             pendingObjects,
                             depRel);
    }

    systable_endscan(scan);

    /*
     * Finally, we can add the target object to targetObjects.  Be careful to
     * include any flags that were passed back down to us from inner recursion
     * levels.
     */
    extra.flags = mystack.flags;
    if (stack)
        extra.dependee = *stack->object;
    else
        memset(&extra.dependee, 0, sizeof(extra.dependee));
    add_exact_object_address_extra(object, &extra, targetObjects);
}

/*
 * reportDependentObjects - report about dependencies, and fail if RESTRICT
 *
 * Tell the user about dependent objects that we are going to delete
 * (or would need to delete, but are prevented by RESTRICT mode);
 * then error out if there are any and it's not CASCADE mode.
 *
 *  targetObjects: list of objects that are scheduled to be deleted
 *  behavior: RESTRICT or CASCADE
 *  flags: other flags for the deletion operation
 *  origObject: base object of deletion, or NULL if not available
 *      (the latter case occurs in DROP OWNED)
 */
static void
reportDependentObjects(const ObjectAddresses *targetObjects,
                       DropBehavior behavior,
                       int flags,
                       const ObjectAddress *origObject)
{
    int         msglevel = (flags & PERFORM_DELETION_QUIETLY) ? DEBUG2 : NOTICE;
    bool        ok = true;
    StringInfoData clientdetail;
    StringInfoData logdetail;
    int         numReportedClient = 0;
    int         numNotReportedClient = 0;
    int         i;

    /*
     * If no error is to be thrown, and the msglevel is too low to be shown to
     * either client or server log, there's no need to do any of the work.
     *
     * Note: this code doesn't know all there is to be known about elog
     * levels, but it works for NOTICE and DEBUG2, which are the only values
     * msglevel can currently have.  We also assume we are running in a normal
     * operating environment.
     */
    if (behavior == DROP_CASCADE &&
        msglevel < client_min_messages &&
        (msglevel < log_min_messages || log_min_messages == LOG))
        return;

    /*
     * We limit the number of dependencies reported to the client to
     * MAX_REPORTED_DEPS, since client software may not deal well with
     * enormous error strings.  The server log always gets a full report.
     */
#define MAX_REPORTED_DEPS 100

    initStringInfo(&clientdetail);
    initStringInfo(&logdetail);

    /*
     * We process the list back to front (ie, in dependency order not deletion
     * order), since this makes for a more understandable display.
     */
    for (i = targetObjects->numrefs - 1; i >= 0; i--)
    {
        const ObjectAddress *obj = &targetObjects->refs[i];
        const ObjectAddressExtra *extra = &targetObjects->extras[i];
        char       *objDesc;

        /* Ignore the original deletion target(s) */
        if (extra->flags & DEPFLAG_ORIGINAL)
            continue;

        objDesc = getObjectDescription(obj);

        /*
         * If, at any stage of the recursive search, we reached the object via
         * an AUTO, INTERNAL, or EXTENSION dependency, then it's okay to
         * delete it even in RESTRICT mode.
         */
        if (extra->flags & (DEPFLAG_AUTO |
                            DEPFLAG_INTERNAL |
                            DEPFLAG_EXTENSION))
        {
            /*
             * auto-cascades are reported at DEBUG2, not msglevel.  We don't
             * try to combine them with the regular message because the
             * results are too confusing when client_min_messages and
             * log_min_messages are different.
             */
            ereport(DEBUG2,
                    (errmsg("drop auto-cascades to %s",
                            objDesc)));
        }
        else if (behavior == DROP_RESTRICT)
        {
            char       *otherDesc = getObjectDescription(&extra->dependee);

            if (numReportedClient < MAX_REPORTED_DEPS)
            {
                /* separate entries with a newline */
                if (clientdetail.len != 0)
                    appendStringInfoChar(&clientdetail, '\n');
                appendStringInfo(&clientdetail, _("%s depends on %s"),
                                 objDesc, otherDesc);
                numReportedClient++;
            }
            else
                numNotReportedClient++;
            /* separate entries with a newline */
            if (logdetail.len != 0)
                appendStringInfoChar(&logdetail, '\n');
            appendStringInfo(&logdetail, _("%s depends on %s"),
                             objDesc, otherDesc);
            pfree(otherDesc);
            ok = false;
        }
        else
        {
            if (numReportedClient < MAX_REPORTED_DEPS)
            {
                /* separate entries with a newline */
                if (clientdetail.len != 0)
                    appendStringInfoChar(&clientdetail, '\n');
                appendStringInfo(&clientdetail, _("drop cascades to %s"),
                                 objDesc);
                numReportedClient++;
            }
            else
                numNotReportedClient++;
            /* separate entries with a newline */
            if (logdetail.len != 0)
                appendStringInfoChar(&logdetail, '\n');
            appendStringInfo(&logdetail, _("drop cascades to %s"),
                             objDesc);
        }

        pfree(objDesc);
    }

    if (numNotReportedClient > 0)
        appendStringInfo(&clientdetail, ngettext("\nand %d other object "
                                                 "(see server log for list)",
                                                 "\nand %d other objects "
                                                 "(see server log for list)",
                                                 numNotReportedClient),
                         numNotReportedClient);

    if (!ok)
    {
        if (origObject)
            ereport(ERROR,
                    (errcode(ERRCODE_DEPENDENT_OBJECTS_STILL_EXIST),
                     errmsg("cannot drop %s because other objects depend on it",
                            getObjectDescription(origObject)),
                     errdetail("%s", clientdetail.data),
                     errdetail_log("%s", logdetail.data),
                     errhint("Use DROP ... CASCADE to drop the dependent objects too.")));
        else
            ereport(ERROR,
                    (errcode(ERRCODE_DEPENDENT_OBJECTS_STILL_EXIST),
                     errmsg("cannot drop desired object(s) because other objects depend on them"),
                     errdetail("%s", clientdetail.data),
                     errdetail_log("%s", logdetail.data),
                     errhint("Use DROP ... CASCADE to drop the dependent objects too.")));
    }
    else if (numReportedClient > 1)
    {
        ereport(msglevel,
        /* translator: %d always has a value larger than 1 */
                (errmsg_plural("drop cascades to %d other object",
                               "drop cascades to %d other objects",
                               numReportedClient + numNotReportedClient,
                               numReportedClient + numNotReportedClient),
                 errdetail("%s", clientdetail.data),
                 errdetail_log("%s", logdetail.data)));
    }
    else if (numReportedClient == 1)
    {
        /* we just use the single item as-is */
        ereport(msglevel,
                (errmsg_internal("%s", clientdetail.data)));
    }

    pfree(clientdetail.data);
    pfree(logdetail.data);
}

/*
 * deleteOneObject: delete a single object for performDeletion.
 *
 * *depRel is the already-open pg_depend relation.
 */
static void
deleteOneObject(const ObjectAddress *object, Relation *depRel, int flags)
{
    ScanKeyData key[3];
    int         nkeys;
    SysScanDesc scan;
    HeapTuple   tup;

    /* DROP hook of the objects being removed */
    InvokeObjectDropHookArg(object->classId, object->objectId,
                            object->objectSubId, flags);

    /*
     * Close depRel if we are doing a drop concurrently.  The object deletion
     * subroutine will commit the current transaction, so we can't keep the
     * relation open across doDeletion().
     */
    if (flags & PERFORM_DELETION_CONCURRENTLY)
        heap_close(*depRel, RowExclusiveLock);

    /*
     * Delete the object itself, in an object-type-dependent way.
     *
     * We used to do this after removing the outgoing dependency links, but it
     * seems just as reasonable to do it beforehand.  In the concurrent case
     * we *must* do it in this order, because we can't make any transactional
     * updates before calling doDeletion() --- they'd get committed right
     * away, which is not cool if the deletion then fails.
     */
    doDeletion(object, flags);

    /*
     * Reopen depRel if we closed it above
     */
    if (flags & PERFORM_DELETION_CONCURRENTLY)
        *depRel = heap_open(DependRelationId, RowExclusiveLock);

    /*
     * Now remove any pg_depend records that link from this object to others.
     * (Any records linking to this object should be gone already.)
     *
     * When dropping a whole object (subId = 0), remove all pg_depend records
     * for its sub-objects too.
     */
    ScanKeyInit(&key[0],
                Anum_pg_depend_classid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(object->classId));
    ScanKeyInit(&key[1],
                Anum_pg_depend_objid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(object->objectId));
    if (object->objectSubId != 0)
    {
        ScanKeyInit(&key[2],
                    Anum_pg_depend_objsubid,
                    BTEqualStrategyNumber, F_INT4EQ,
                    Int32GetDatum(object->objectSubId));
        nkeys = 3;
    }
    else
        nkeys = 2;

    scan = systable_beginscan(*depRel, DependDependerIndexId, true,
                              NULL, nkeys, key);

    while (HeapTupleIsValid(tup = systable_getnext(scan)))
    {
        CatalogTupleDelete(*depRel, &tup->t_self);
    }

    systable_endscan(scan);

    /*
     * Delete shared dependency references related to this object.  Again, if
     * subId = 0, remove records for sub-objects too.
     */
    deleteSharedDependencyRecordsFor(object->classId, object->objectId,
                                     object->objectSubId);


    /*
     * Delete any comments, security labels, or initial privileges associated
     * with this object.  (This is a convenient place to do these things,
     * rather than having every object type know to do it.)
     */
    DeleteComments(object->objectId, object->classId, object->objectSubId);
    DeleteSecurityLabel(object);
    DeleteInitPrivs(object);

    /*
     * CommandCounterIncrement here to ensure that preceding changes are all
     * visible to the next deletion step.
     */
    CommandCounterIncrement();

    /*
     * And we're done!
     */
}

/*
 * doDeletion: actually delete a single object
 */
static void
doDeletion(const ObjectAddress *object, int flags)
{
    switch (getObjectClass(object))
    {
        case OCLASS_CLASS:
            {
                char        relKind = get_rel_relkind(object->objectId);

                if (relKind == RELKIND_INDEX ||
                    relKind == RELKIND_PARTITIONED_INDEX)
                {
                    bool        concurrent = ((flags & PERFORM_DELETION_CONCURRENTLY) != 0);

                    Assert(object->objectSubId == 0);
                    index_drop(object->objectId, concurrent);
                }
                else
                {
                    if (object->objectSubId != 0)
                        RemoveAttributeById(object->objectId,
                                            object->objectSubId);
                    else
                        heap_drop_with_catalog(object->objectId);
                }

                /*
                 * for a sequence, in addition to dropping the heap, also
                 * delete pg_sequence tuple
                 */
                if (relKind == RELKIND_SEQUENCE)
                    DeleteSequenceTuple(object->objectId);
                break;
            }

        case OCLASS_PROC:
            RemoveFunctionById(object->objectId);
            break;

        case OCLASS_TYPE:
            RemoveTypeById(object->objectId);
            break;

        case OCLASS_CAST:
            DropCastById(object->objectId);
            break;

        case OCLASS_COLLATION:
            RemoveCollationById(object->objectId);
            break;

        case OCLASS_CONSTRAINT:
            RemoveConstraintById(object->objectId);
            break;

        case OCLASS_CONVERSION:
            RemoveConversionById(object->objectId);
            break;

        case OCLASS_DEFAULT:
            RemoveAttrDefaultById(object->objectId);
            break;

        case OCLASS_LANGUAGE:
            DropProceduralLanguageById(object->objectId);
            break;

        case OCLASS_LARGEOBJECT:
            LargeObjectDrop(object->objectId);
            break;

        case OCLASS_OPERATOR:
            RemoveOperatorById(object->objectId);
            break;

        case OCLASS_OPCLASS:
            RemoveOpClassById(object->objectId);
            break;

        case OCLASS_OPFAMILY:
            RemoveOpFamilyById(object->objectId);
            break;

        case OCLASS_AM:
            RemoveAccessMethodById(object->objectId);
            break;

        case OCLASS_AMOP:
            RemoveAmOpEntryById(object->objectId);
            break;

        case OCLASS_AMPROC:
            RemoveAmProcEntryById(object->objectId);
            break;

        case OCLASS_REWRITE:
            RemoveRewriteRuleById(object->objectId);
            break;

        case OCLASS_TRIGGER:
            RemoveTriggerById(object->objectId);
            break;

        case OCLASS_SCHEMA:
            RemoveSchemaById(object->objectId);
            break;

        case OCLASS_STATISTIC_EXT:
            RemoveStatisticsById(object->objectId);
            break;

        case OCLASS_TSPARSER:
            RemoveTSParserById(object->objectId);
            break;

        case OCLASS_TSDICT:
            RemoveTSDictionaryById(object->objectId);
            break;

        case OCLASS_TSTEMPLATE:
            RemoveTSTemplateById(object->objectId);
            break;

        case OCLASS_TSCONFIG:
            RemoveTSConfigurationById(object->objectId);
            break;

            /*
             * OCLASS_ROLE, OCLASS_DATABASE, OCLASS_TBLSPACE intentionally not
             * handled here
             */

        case OCLASS_FDW:
            RemoveForeignDataWrapperById(object->objectId);
            break;

        case OCLASS_FOREIGN_SERVER:
            RemoveForeignServerById(object->objectId);
            break;

        case OCLASS_USER_MAPPING:
            RemoveUserMappingById(object->objectId);
            break;

        case OCLASS_DEFACL:
            RemoveDefaultACLById(object->objectId);
            break;

        case OCLASS_EXTENSION:
            RemoveExtensionById(object->objectId);
            break;

        case OCLASS_EVENT_TRIGGER:
            RemoveEventTriggerById(object->objectId);
            break;

        case OCLASS_POLICY:
            RemovePolicyById(object->objectId);
            break;

        case OCLASS_PUBLICATION:
            RemovePublicationById(object->objectId);
            break;

        case OCLASS_PUBLICATION_REL:
            RemovePublicationRelById(object->objectId);
            break;

        case OCLASS_TRANSFORM:
            DropTransformById(object->objectId);
            break;

            /*
             * These global object types are not supported here.
             */
        case OCLASS_ROLE:
        case OCLASS_DATABASE:
        case OCLASS_TBLSPACE:
        case OCLASS_SUBSCRIPTION:
            elog(ERROR, "global objects cannot be deleted by doDeletion");
            break;

            /*
             * There's intentionally no default: case here; we want the
             * compiler to warn if a new OCLASS hasn't been handled above.
             */
    }
}

/*
 * AcquireDeletionLock - acquire a suitable lock for deleting an object
 *
 * We use LockRelation for relations, LockDatabaseObject for everything
 * else.  Note that dependency.c is not concerned with deleting any kind of
 * shared-across-databases object, so we have no need for LockSharedObject.
 */
static void
AcquireDeletionLock(const ObjectAddress *object, int flags)
{
    if (object->classId == RelationRelationId)
    {
        /*
         * In DROP INDEX CONCURRENTLY, take only ShareUpdateExclusiveLock on
         * the index for the moment.  index_drop() will promote the lock once
         * it's safe to do so.  In all other cases we need full exclusive
         * lock.
         */
        if (flags & PERFORM_DELETION_CONCURRENTLY)
            LockRelationOid(object->objectId, ShareUpdateExclusiveLock);
        else
            LockRelationOid(object->objectId, AccessExclusiveLock);
    }
    else
    {
        /* assume we should lock the whole object not a sub-object */
        LockDatabaseObject(object->classId, object->objectId, 0,
                           AccessExclusiveLock);
    }
}

/*
 * ReleaseDeletionLock - release an object deletion lock
 */
static void
ReleaseDeletionLock(const ObjectAddress *object)
{
    if (object->classId == RelationRelationId)
        UnlockRelationOid(object->objectId, AccessExclusiveLock);
    else
        /* assume we should lock the whole object not a sub-object */
        UnlockDatabaseObject(object->classId, object->objectId, 0,
                             AccessExclusiveLock);
}

/*
 * recordDependencyOnExpr - find expression dependencies
 *
 * This is used to find the dependencies of rules, constraint expressions,
 * etc.
 *
 * Given an expression or query in node-tree form, find all the objects
 * it refers to (tables, columns, operators, functions, etc).  Record
 * a dependency of the specified type from the given depender object
 * to each object mentioned in the expression.
 *
 * rtable is the rangetable to be used to interpret Vars with varlevelsup=0.
 * It can be NIL if no such variables are expected.
 */
void
recordDependencyOnExpr(const ObjectAddress *depender,
                       Node *expr, List *rtable,
                       DependencyType behavior)
{
    find_expr_references_context context;

    context.addrs = new_object_addresses();

    /* Set up interpretation for Vars at varlevelsup = 0 */
    context.rtables = list_make1(rtable);

    /* Scan the expression tree for referenceable objects */
    find_expr_references_walker(expr, &context);

    /* Remove any duplicates */
    eliminate_duplicate_dependencies(context.addrs);

    /* And record 'em */
    recordMultipleDependencies(depender,
                               context.addrs->refs, context.addrs->numrefs,
                               behavior);

    free_object_addresses(context.addrs);
}

/*
 * recordDependencyOnSingleRelExpr - find expression dependencies
 *
 * As above, but only one relation is expected to be referenced (with
 * varno = 1 and varlevelsup = 0).  Pass the relation OID instead of a
 * range table.  An additional frammish is that dependencies on that
 * relation (or its component columns) will be marked with 'self_behavior',
 * whereas 'behavior' is used for everything else.
 *
 * NOTE: the caller should ensure that a whole-table dependency on the
 * specified relation is created separately, if one is needed.  In particular,
 * a whole-row Var "relation.*" will not cause this routine to emit any
 * dependency item.  This is appropriate behavior for subexpressions of an
 * ordinary query, so other cases need to cope as necessary.
 */
void
recordDependencyOnSingleRelExpr(const ObjectAddress *depender,
                                Node *expr, Oid relId,
                                DependencyType behavior,
                                DependencyType self_behavior,
                                bool ignore_self)
{
    find_expr_references_context context;
    RangeTblEntry rte;

    context.addrs = new_object_addresses();

    /* We gin up a rather bogus rangetable list to handle Vars */
    MemSet(&rte, 0, sizeof(rte));
    rte.type = T_RangeTblEntry;
    rte.rtekind = RTE_RELATION;
    rte.relid = relId;
    rte.relkind = RELKIND_RELATION; /* no need for exactness here */

    context.rtables = list_make1(list_make1(&rte));

    /* Scan the expression tree for referenceable objects */
    find_expr_references_walker(expr, &context);

    /* Remove any duplicates */
    eliminate_duplicate_dependencies(context.addrs);

    /* Separate self-dependencies if necessary */
    if (behavior != self_behavior && context.addrs->numrefs > 0)
    {
        ObjectAddresses *self_addrs;
        ObjectAddress *outobj;
        int         oldref,
                    outrefs;

        self_addrs = new_object_addresses();

        outobj = context.addrs->refs;
        outrefs = 0;
        for (oldref = 0; oldref < context.addrs->numrefs; oldref++)
        {
            ObjectAddress *thisobj = context.addrs->refs + oldref;

            if (thisobj->classId == RelationRelationId &&
                thisobj->objectId == relId)
            {
                /* Move this ref into self_addrs */
                add_exact_object_address(thisobj, self_addrs);
            }
            else
            {
                /* Keep it in context.addrs */
                *outobj = *thisobj;
                outobj++;
                outrefs++;
            }
        }
        context.addrs->numrefs = outrefs;

        /* Record the self-dependencies */
        if (!ignore_self)
            recordMultipleDependencies(depender,
                                       self_addrs->refs, self_addrs->numrefs,
                                       self_behavior);

        free_object_addresses(self_addrs);
    }

    /* Record the external dependencies */
    recordMultipleDependencies(depender,
                               context.addrs->refs, context.addrs->numrefs,
                               behavior);

    free_object_addresses(context.addrs);
}

/*
 * Recursively search an expression tree for object references.
 *
 * Note: we avoid creating references to columns of tables that participate
 * in an SQL JOIN construct, but are not actually used anywhere in the query.
 * To do so, we do not scan the joinaliasvars list of a join RTE while
 * scanning the query rangetable, but instead scan each individual entry
 * of the alias list when we find a reference to it.
 *
 * Note: in many cases we do not need to create dependencies on the datatypes
 * involved in an expression, because we'll have an indirect dependency via
 * some other object.  For instance Var nodes depend on a column which depends
 * on the datatype, and OpExpr nodes depend on the operator which depends on
 * the datatype.  However we do need a type dependency if there is no such
 * indirect dependency, as for example in Const and CoerceToDomain nodes.
 *
 * Similarly, we don't need to create dependencies on collations except where
 * the collation is being freshly introduced to the expression.
 */
static bool
find_expr_references_walker(Node *node,
                            find_expr_references_context *context)
{
    if (node == NULL)
        return false;
    if (IsA(node, Var))
    {
        Var        *var = (Var *) node;
        List       *rtable;
        RangeTblEntry *rte;

        /* Find matching rtable entry, or complain if not found */
        if (var->varlevelsup >= list_length(context->rtables))
            elog(ERROR, "invalid varlevelsup %d", var->varlevelsup);
        rtable = (List *) list_nth(context->rtables, var->varlevelsup);
        if (var->varno <= 0 || var->varno > list_length(rtable))
            elog(ERROR, "invalid varno %d", var->varno);
        rte = rt_fetch(var->varno, rtable);

        /*
         * A whole-row Var references no specific columns, so adds no new
         * dependency.  (We assume that there is a whole-table dependency
         * arising from each underlying rangetable entry.  While we could
         * record such a dependency when finding a whole-row Var that
         * references a relation directly, it's quite unclear how to extend
         * that to whole-row Vars for JOINs, so it seems better to leave the
         * responsibility with the range table.  Note that this poses some
         * risks for identifying dependencies of stand-alone expressions:
         * whole-table references may need to be created separately.)
         */
        if (var->varattno == InvalidAttrNumber)
            return false;
        if (rte->rtekind == RTE_RELATION)
        {
            /* If it's a plain relation, reference this column */
            add_object_address(OCLASS_CLASS, rte->relid, var->varattno,
                               context->addrs);
        }
        else if (rte->rtekind == RTE_JOIN)
        {
            /* Scan join output column to add references to join inputs */
            List       *save_rtables;

            /* We must make the context appropriate for join's level */
            save_rtables = context->rtables;
            context->rtables = list_copy_tail(context->rtables,
                                              var->varlevelsup);
            if (var->varattno <= 0 ||
                var->varattno > list_length(rte->joinaliasvars))
                elog(ERROR, "invalid varattno %d", var->varattno);
            find_expr_references_walker((Node *) list_nth(rte->joinaliasvars,
                                                          var->varattno - 1),
                                        context);
            list_free(context->rtables);
            context->rtables = save_rtables;
        }
        return false;
    }
    else if (IsA(node, Const))
    {
        Const      *con = (Const *) node;
        Oid         objoid;

        /* A constant must depend on the constant's datatype */
        add_object_address(OCLASS_TYPE, con->consttype, 0,
                           context->addrs);

        /*
         * We must also depend on the constant's collation: it could be
         * different from the datatype's, if a CollateExpr was const-folded to
         * a simple constant.  However we can save work in the most common
         * case where the collation is "default", since we know that's pinned.
         */
        if (OidIsValid(con->constcollid) &&
            con->constcollid != DEFAULT_COLLATION_OID)
            add_object_address(OCLASS_COLLATION, con->constcollid, 0,
                               context->addrs);

        /*
         * If it's a regclass or similar literal referring to an existing
         * object, add a reference to that object.  (Currently, only the
         * regclass and regconfig cases have any likely use, but we may as
         * well handle all the OID-alias datatypes consistently.)
         */
        if (!con->constisnull)
        {
            switch (con->consttype)
            {
                case REGPROCOID:
                case REGPROCEDUREOID:
                    objoid = DatumGetObjectId(con->constvalue);
                    if (SearchSysCacheExists1(PROCOID,
                                              ObjectIdGetDatum(objoid)))
                        add_object_address(OCLASS_PROC, objoid, 0,
                                           context->addrs);
                    break;
                case REGOPEROID:
                case REGOPERATOROID:
                    objoid = DatumGetObjectId(con->constvalue);
                    if (SearchSysCacheExists1(OPEROID,
                                              ObjectIdGetDatum(objoid)))
                        add_object_address(OCLASS_OPERATOR, objoid, 0,
                                           context->addrs);
                    break;
                case REGCLASSOID:
                    objoid = DatumGetObjectId(con->constvalue);
                    if (SearchSysCacheExists1(RELOID,
                                              ObjectIdGetDatum(objoid)))
                        add_object_address(OCLASS_CLASS, objoid, 0,
                                           context->addrs);
                    break;
                case REGTYPEOID:
                    objoid = DatumGetObjectId(con->constvalue);
                    if (SearchSysCacheExists1(TYPEOID,
                                              ObjectIdGetDatum(objoid)))
                        add_object_address(OCLASS_TYPE, objoid, 0,
                                           context->addrs);
                    break;
                case REGCONFIGOID:
                    objoid = DatumGetObjectId(con->constvalue);
                    if (SearchSysCacheExists1(TSCONFIGOID,
                                              ObjectIdGetDatum(objoid)))
                        add_object_address(OCLASS_TSCONFIG, objoid, 0,
                                           context->addrs);
                    break;
                case REGDICTIONARYOID:
                    objoid = DatumGetObjectId(con->constvalue);
                    if (SearchSysCacheExists1(TSDICTOID,
                                              ObjectIdGetDatum(objoid)))
                        add_object_address(OCLASS_TSDICT, objoid, 0,
                                           context->addrs);
                    break;

                case REGNAMESPACEOID:
                    objoid = DatumGetObjectId(con->constvalue);
                    if (SearchSysCacheExists1(NAMESPACEOID,
                                              ObjectIdGetDatum(objoid)))
                        add_object_address(OCLASS_SCHEMA, objoid, 0,
                                           context->addrs);
                    break;

                    /*
                     * Dependencies for regrole should be shared among all
                     * databases, so explicitly inhibit to have dependencies.
                     */
                case REGROLEOID:
                    ereport(ERROR,
                            (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                             errmsg("constant of the type %s cannot be used here",
                                    "regrole")));
                    break;
            }
        }
        return false;
    }
    else if (IsA(node, Param))
    {
        Param      *param = (Param *) node;

        /* A parameter must depend on the parameter's datatype */
        add_object_address(OCLASS_TYPE, param->paramtype, 0,
                           context->addrs);
        /* and its collation, just as for Consts */
        if (OidIsValid(param->paramcollid) &&
            param->paramcollid != DEFAULT_COLLATION_OID)
            add_object_address(OCLASS_COLLATION, param->paramcollid, 0,
                               context->addrs);
    }
    else if (IsA(node, FuncExpr))
    {
        FuncExpr   *funcexpr = (FuncExpr *) node;

        add_object_address(OCLASS_PROC, funcexpr->funcid, 0,
                           context->addrs);
        /* fall through to examine arguments */
    }
    else if (IsA(node, OpExpr))
    {
        OpExpr     *opexpr = (OpExpr *) node;

        add_object_address(OCLASS_OPERATOR, opexpr->opno, 0,
                           context->addrs);
        /* fall through to examine arguments */
    }
    else if (IsA(node, DistinctExpr))
    {
        DistinctExpr *distinctexpr = (DistinctExpr *) node;

        add_object_address(OCLASS_OPERATOR, distinctexpr->opno, 0,
                           context->addrs);
        /* fall through to examine arguments */
    }
    else if (IsA(node, NullIfExpr))
    {
        NullIfExpr *nullifexpr = (NullIfExpr *) node;

        add_object_address(OCLASS_OPERATOR, nullifexpr->opno, 0,
                           context->addrs);
        /* fall through to examine arguments */
    }
    else if (IsA(node, ScalarArrayOpExpr))
    {
        ScalarArrayOpExpr *opexpr = (ScalarArrayOpExpr *) node;

        add_object_address(OCLASS_OPERATOR, opexpr->opno, 0,
                           context->addrs);
        /* fall through to examine arguments */
    }
    else if (IsA(node, Aggref))
    {
        Aggref     *aggref = (Aggref *) node;

        add_object_address(OCLASS_PROC, aggref->aggfnoid, 0,
                           context->addrs);
        /* fall through to examine arguments */
    }
    else if (IsA(node, WindowFunc))
    {
        WindowFunc *wfunc = (WindowFunc *) node;

        add_object_address(OCLASS_PROC, wfunc->winfnoid, 0,
                           context->addrs);
        /* fall through to examine arguments */
    }
    else if (IsA(node, SubPlan))
    {
        /* Extra work needed here if we ever need this case */
        elog(ERROR, "already-planned subqueries not supported");
    }
    else if (IsA(node, FieldSelect))
    {
        FieldSelect *fselect = (FieldSelect *) node;
        Oid         argtype = getBaseType(exprType((Node *) fselect->arg));
        Oid         reltype = get_typ_typrelid(argtype);

        /*
         * We need a dependency on the specific column named in FieldSelect,
         * assuming we can identify the pg_class OID for it.  (Probably we
         * always can at the moment, but in future it might be possible for
         * argtype to be RECORDOID.)  If we can make a column dependency then
         * we shouldn't need a dependency on the column's type; but if we
         * can't, make a dependency on the type, as it might not appear
         * anywhere else in the expression.
         */
        if (OidIsValid(reltype))
            add_object_address(OCLASS_CLASS, reltype, fselect->fieldnum,
                               context->addrs);
        else
            add_object_address(OCLASS_TYPE, fselect->resulttype, 0,
                               context->addrs);
        /* the collation might not be referenced anywhere else, either */
        if (OidIsValid(fselect->resultcollid) &&
            fselect->resultcollid != DEFAULT_COLLATION_OID)
            add_object_address(OCLASS_COLLATION, fselect->resultcollid, 0,
                               context->addrs);
    }
    else if (IsA(node, FieldStore))
    {
        FieldStore *fstore = (FieldStore *) node;
        Oid         reltype = get_typ_typrelid(fstore->resulttype);

        /* similar considerations to FieldSelect, but multiple column(s) */
        if (OidIsValid(reltype))
        {
            ListCell   *l;

            foreach(l, fstore->fieldnums)
                add_object_address(OCLASS_CLASS, reltype, lfirst_int(l),
                                   context->addrs);
        }
        else
            add_object_address(OCLASS_TYPE, fstore->resulttype, 0,
                               context->addrs);
    }
    else if (IsA(node, RelabelType))
    {
        RelabelType *relab = (RelabelType *) node;

        /* since there is no function dependency, need to depend on type */
        add_object_address(OCLASS_TYPE, relab->resulttype, 0,
                           context->addrs);
        /* the collation might not be referenced anywhere else, either */
        if (OidIsValid(relab->resultcollid) &&
            relab->resultcollid != DEFAULT_COLLATION_OID)
            add_object_address(OCLASS_COLLATION, relab->resultcollid, 0,
                               context->addrs);
    }
    else if (IsA(node, CoerceViaIO))
    {
        CoerceViaIO *iocoerce = (CoerceViaIO *) node;

        /* since there is no exposed function, need to depend on type */
        add_object_address(OCLASS_TYPE, iocoerce->resulttype, 0,
                           context->addrs);
        /* the collation might not be referenced anywhere else, either */
        if (OidIsValid(iocoerce->resultcollid) &&
            iocoerce->resultcollid != DEFAULT_COLLATION_OID)
            add_object_address(OCLASS_COLLATION, iocoerce->resultcollid, 0,
                               context->addrs);
    }
    else if (IsA(node, ArrayCoerceExpr))
    {
        ArrayCoerceExpr *acoerce = (ArrayCoerceExpr *) node;

        /* as above, depend on type */
        add_object_address(OCLASS_TYPE, acoerce->resulttype, 0,
                           context->addrs);
        /* the collation might not be referenced anywhere else, either */
        if (OidIsValid(acoerce->resultcollid) &&
            acoerce->resultcollid != DEFAULT_COLLATION_OID)
            add_object_address(OCLASS_COLLATION, acoerce->resultcollid, 0,
                               context->addrs);
        /* fall through to examine arguments */
    }
    else if (IsA(node, ConvertRowtypeExpr))
    {
        ConvertRowtypeExpr *cvt = (ConvertRowtypeExpr *) node;

        /* since there is no function dependency, need to depend on type */
        add_object_address(OCLASS_TYPE, cvt->resulttype, 0,
                           context->addrs);
    }
    else if (IsA(node, CollateExpr))
    {
        CollateExpr *coll = (CollateExpr *) node;

        add_object_address(OCLASS_COLLATION, coll->collOid, 0,
                           context->addrs);
    }
    else if (IsA(node, RowExpr))
    {
        RowExpr    *rowexpr = (RowExpr *) node;

        add_object_address(OCLASS_TYPE, rowexpr->row_typeid, 0,
                           context->addrs);
    }
    else if (IsA(node, RowCompareExpr))
    {
        RowCompareExpr *rcexpr = (RowCompareExpr *) node;
        ListCell   *l;

        foreach(l, rcexpr->opnos)
        {
            add_object_address(OCLASS_OPERATOR, lfirst_oid(l), 0,
                               context->addrs);
        }
        foreach(l, rcexpr->opfamilies)
        {
            add_object_address(OCLASS_OPFAMILY, lfirst_oid(l), 0,
                               context->addrs);
        }
        /* fall through to examine arguments */
    }
    else if (IsA(node, CoerceToDomain))
    {
        CoerceToDomain *cd = (CoerceToDomain *) node;

        add_object_address(OCLASS_TYPE, cd->resulttype, 0,
                           context->addrs);
    }
    else if (IsA(node, NextValueExpr))
    {
        NextValueExpr *nve = (NextValueExpr *) node;

        add_object_address(OCLASS_CLASS, nve->seqid, 0,
                           context->addrs);
    }
    else if (IsA(node, OnConflictExpr))
    {
        OnConflictExpr *onconflict = (OnConflictExpr *) node;

        if (OidIsValid(onconflict->constraint))
            add_object_address(OCLASS_CONSTRAINT, onconflict->constraint, 0,
                               context->addrs);
        /* fall through to examine arguments */
    }
    else if (IsA(node, SortGroupClause))
    {
        SortGroupClause *sgc = (SortGroupClause *) node;

        add_object_address(OCLASS_OPERATOR, sgc->eqop, 0,
                           context->addrs);
        if (OidIsValid(sgc->sortop))
            add_object_address(OCLASS_OPERATOR, sgc->sortop, 0,
                               context->addrs);
        return false;
    }
    else if (IsA(node, WindowClause))
    {
        WindowClause *wc = (WindowClause *) node;

        if (OidIsValid(wc->startInRangeFunc))
            add_object_address(OCLASS_PROC, wc->startInRangeFunc, 0,
                               context->addrs);
        if (OidIsValid(wc->endInRangeFunc))
            add_object_address(OCLASS_PROC, wc->endInRangeFunc, 0,
                               context->addrs);
        if (OidIsValid(wc->inRangeColl) &&
            wc->inRangeColl != DEFAULT_COLLATION_OID)
            add_object_address(OCLASS_COLLATION, wc->inRangeColl, 0,
                               context->addrs);
        /* fall through to examine substructure */
    }
    else if (IsA(node, Query))
    {
        /* Recurse into RTE subquery or not-yet-planned sublink subquery */
        Query      *query = (Query *) node;
        ListCell   *lc;
        bool        result;

        /*
         * Add whole-relation refs for each plain relation mentioned in the
         * subquery's rtable.
         *
         * Note: query_tree_walker takes care of recursing into RTE_FUNCTION
         * RTEs, subqueries, etc, so no need to do that here.  But keep it
         * from looking at join alias lists.
         *
         * Note: we don't need to worry about collations mentioned in
         * RTE_VALUES or RTE_CTE RTEs, because those must just duplicate
         * collations referenced in other parts of the Query.  We do have to
         * worry about collations mentioned in RTE_FUNCTION, but we take care
         * of those when we recurse to the RangeTblFunction node(s).
         */
        foreach(lc, query->rtable)
        {
            RangeTblEntry *rte = (RangeTblEntry *) lfirst(lc);

            switch (rte->rtekind)
            {
                case RTE_RELATION:
                    add_object_address(OCLASS_CLASS, rte->relid, 0,
                                       context->addrs);
                    break;
                default:
                    break;
            }
        }

        /*
         * If the query is an INSERT or UPDATE, we should create a dependency
         * on each target column, to prevent the specific target column from
         * being dropped.  Although we will visit the TargetEntry nodes again
         * during query_tree_walker, we won't have enough context to do this
         * conveniently, so do it here.
         */
        if (query->commandType == CMD_INSERT ||
            query->commandType == CMD_UPDATE)
        {
            RangeTblEntry *rte;

            if (query->resultRelation <= 0 ||
                query->resultRelation > list_length(query->rtable))
                elog(ERROR, "invalid resultRelation %d",
                     query->resultRelation);
            rte = rt_fetch(query->resultRelation, query->rtable);
            if (rte->rtekind == RTE_RELATION)
            {
                foreach(lc, query->targetList)
                {
                    TargetEntry *tle = (TargetEntry *) lfirst(lc);

                    if (tle->resjunk)
                        continue;   /* ignore junk tlist items */
                    add_object_address(OCLASS_CLASS, rte->relid, tle->resno,
                                       context->addrs);
                }
            }
        }

        /*
         * Add dependencies on constraints listed in query's constraintDeps
         */
        foreach(lc, query->constraintDeps)
        {
            add_object_address(OCLASS_CONSTRAINT, lfirst_oid(lc), 0,
                               context->addrs);
        }

        /* query_tree_walker ignores ORDER BY etc, but we need those opers */
        find_expr_references_walker((Node *) query->sortClause, context);
        find_expr_references_walker((Node *) query->groupClause, context);
        find_expr_references_walker((Node *) query->windowClause, context);
        find_expr_references_walker((Node *) query->distinctClause, context);

        /* Examine substructure of query */
        context->rtables = lcons(query->rtable, context->rtables);
        result = query_tree_walker(query,
                                   find_expr_references_walker,
                                   (void *) context,
                                   QTW_IGNORE_JOINALIASES);
        context->rtables = list_delete_first(context->rtables);
        return result;
    }
    else if (IsA(node, SetOperationStmt))
    {
        SetOperationStmt *setop = (SetOperationStmt *) node;

        /* we need to look at the groupClauses for operator references */
        find_expr_references_walker((Node *) setop->groupClauses, context);
        /* fall through to examine child nodes */
    }
    else if (IsA(node, RangeTblFunction))
    {
        RangeTblFunction *rtfunc = (RangeTblFunction *) node;
        ListCell   *ct;

        /*
         * Add refs for any datatypes and collations used in a column
         * definition list for a RECORD function.  (For other cases, it should
         * be enough to depend on the function itself.)
         */
        foreach(ct, rtfunc->funccoltypes)
        {
            add_object_address(OCLASS_TYPE, lfirst_oid(ct), 0,
                               context->addrs);
        }
        foreach(ct, rtfunc->funccolcollations)
        {
            Oid         collid = lfirst_oid(ct);

            if (OidIsValid(collid) && collid != DEFAULT_COLLATION_OID)
                add_object_address(OCLASS_COLLATION, collid, 0,
                                   context->addrs);
        }
    }
    else if (IsA(node, TableSampleClause))
    {
        TableSampleClause *tsc = (TableSampleClause *) node;

        add_object_address(OCLASS_PROC, tsc->tsmhandler, 0,
                           context->addrs);
        /* fall through to examine arguments */
    }

    return expression_tree_walker(node, find_expr_references_walker,
                                  (void *) context);
}

/*
 * Given an array of dependency references, eliminate any duplicates.
 */
static void
eliminate_duplicate_dependencies(ObjectAddresses *addrs)
{
    ObjectAddress *priorobj;
    int         oldref,
                newrefs;

    /*
     * We can't sort if the array has "extra" data, because there's no way to
     * keep it in sync.  Fortunately that combination of features is not
     * needed.
     */
    Assert(!addrs->extras);

    if (addrs->numrefs <= 1)
        return;                 /* nothing to do */

    /* Sort the refs so that duplicates are adjacent */
    qsort((void *) addrs->refs, addrs->numrefs, sizeof(ObjectAddress),
          object_address_comparator);

    /* Remove dups */
    priorobj = addrs->refs;
    newrefs = 1;
    for (oldref = 1; oldref < addrs->numrefs; oldref++)
    {
        ObjectAddress *thisobj = addrs->refs + oldref;

        if (priorobj->classId == thisobj->classId &&
            priorobj->objectId == thisobj->objectId)
        {
            if (priorobj->objectSubId == thisobj->objectSubId)
                continue;       /* identical, so drop thisobj */

            /*
             * If we have a whole-object reference and a reference to a part
             * of the same object, we don't need the whole-object reference
             * (for example, we don't need to reference both table foo and
             * column foo.bar).  The whole-object reference will always appear
             * first in the sorted list.
             */
            if (priorobj->objectSubId == 0)
            {
                /* replace whole ref with partial */
                priorobj->objectSubId = thisobj->objectSubId;
                continue;
            }
        }
        /* Not identical, so add thisobj to output set */
        priorobj++;
        *priorobj = *thisobj;
        newrefs++;
    }

    addrs->numrefs = newrefs;
}

/*
 * qsort comparator for ObjectAddress items
 */
static int
object_address_comparator(const void *a, const void *b)
{
    const ObjectAddress *obja = (const ObjectAddress *) a;
    const ObjectAddress *objb = (const ObjectAddress *) b;

    if (obja->classId < objb->classId)
        return -1;
    if (obja->classId > objb->classId)
        return 1;
    if (obja->objectId < objb->objectId)
        return -1;
    if (obja->objectId > objb->objectId)
        return 1;

    /*
     * We sort the subId as an unsigned int so that 0 will come first. See
     * logic in eliminate_duplicate_dependencies.
     */
    if ((unsigned int) obja->objectSubId < (unsigned int) objb->objectSubId)
        return -1;
    if ((unsigned int) obja->objectSubId > (unsigned int) objb->objectSubId)
        return 1;
    return 0;
}

/*
 * Routines for handling an expansible array of ObjectAddress items.
 *
 * new_object_addresses: create a new ObjectAddresses array.
 */
ObjectAddresses *
new_object_addresses(void)
{
    ObjectAddresses *addrs;

    addrs = palloc(sizeof(ObjectAddresses));

    addrs->numrefs = 0;
    addrs->maxrefs = 32;
    addrs->refs = (ObjectAddress *)
        palloc(addrs->maxrefs * sizeof(ObjectAddress));
    addrs->extras = NULL;       /* until/unless needed */

    return addrs;
}

/*
 * Add an entry to an ObjectAddresses array.
 *
 * It is convenient to specify the class by ObjectClass rather than directly
 * by catalog OID.
 */
static void
add_object_address(ObjectClass oclass, Oid objectId, int32 subId,
                   ObjectAddresses *addrs)
{
    ObjectAddress *item;

    /*
     * Make sure object_classes is kept up to date with the ObjectClass enum.
     */
    StaticAssertStmt(lengthof(object_classes) == LAST_OCLASS + 1,
                     "object_classes[] must cover all ObjectClasses");

    /* enlarge array if needed */
    if (addrs->numrefs >= addrs->maxrefs)
    {
        addrs->maxrefs *= 2;
        addrs->refs = (ObjectAddress *)
            repalloc(addrs->refs, addrs->maxrefs * sizeof(ObjectAddress));
        Assert(!addrs->extras);
    }
    /* record this item */
    item = addrs->refs + addrs->numrefs;
    item->classId = object_classes[oclass];
    item->objectId = objectId;
    item->objectSubId = subId;
    addrs->numrefs++;
}

/*
 * Add an entry to an ObjectAddresses array.
 *
 * As above, but specify entry exactly.
 */
void
add_exact_object_address(const ObjectAddress *object,
                         ObjectAddresses *addrs)
{
    ObjectAddress *item;

    /* enlarge array if needed */
    if (addrs->numrefs >= addrs->maxrefs)
    {
        addrs->maxrefs *= 2;
        addrs->refs = (ObjectAddress *)
            repalloc(addrs->refs, addrs->maxrefs * sizeof(ObjectAddress));
        Assert(!addrs->extras);
    }
    /* record this item */
    item = addrs->refs + addrs->numrefs;
    *item = *object;
    addrs->numrefs++;
}

/*
 * Add an entry to an ObjectAddresses array.
 *
 * As above, but specify entry exactly and provide some "extra" data too.
 */
static void
add_exact_object_address_extra(const ObjectAddress *object,
                               const ObjectAddressExtra *extra,
                               ObjectAddresses *addrs)
{
    ObjectAddress *item;
    ObjectAddressExtra *itemextra;

    /* allocate extra space if first time */
    if (!addrs->extras)
        addrs->extras = (ObjectAddressExtra *)
            palloc(addrs->maxrefs * sizeof(ObjectAddressExtra));

    /* enlarge array if needed */
    if (addrs->numrefs >= addrs->maxrefs)
    {
        addrs->maxrefs *= 2;
        addrs->refs = (ObjectAddress *)
            repalloc(addrs->refs, addrs->maxrefs * sizeof(ObjectAddress));
        addrs->extras = (ObjectAddressExtra *)
            repalloc(addrs->extras, addrs->maxrefs * sizeof(ObjectAddressExtra));
    }
    /* record this item */
    item = addrs->refs + addrs->numrefs;
    *item = *object;
    itemextra = addrs->extras + addrs->numrefs;
    *itemextra = *extra;
    addrs->numrefs++;
}

/*
 * Test whether an object is present in an ObjectAddresses array.
 *
 * We return "true" if object is a subobject of something in the array, too.
 */
bool
object_address_present(const ObjectAddress *object,
                       const ObjectAddresses *addrs)
{
    int         i;

    for (i = addrs->numrefs - 1; i >= 0; i--)
    {
        const ObjectAddress *thisobj = addrs->refs + i;

        if (object->classId == thisobj->classId &&
            object->objectId == thisobj->objectId)
        {
            if (object->objectSubId == thisobj->objectSubId ||
                thisobj->objectSubId == 0)
                return true;
        }
    }

    return false;
}

/*
 * As above, except that if the object is present then also OR the given
 * flags into its associated extra data (which must exist).
 */
static bool
object_address_present_add_flags(const ObjectAddress *object,
                                 int flags,
                                 ObjectAddresses *addrs)
{
    bool        result = false;
    int         i;

    for (i = addrs->numrefs - 1; i >= 0; i--)
    {
        ObjectAddress *thisobj = addrs->refs + i;

        if (object->classId == thisobj->classId &&
            object->objectId == thisobj->objectId)
        {
            if (object->objectSubId == thisobj->objectSubId)
            {
                ObjectAddressExtra *thisextra = addrs->extras + i;

                thisextra->flags |= flags;
                result = true;
            }
            else if (thisobj->objectSubId == 0)
            {
                /*
                 * We get here if we find a need to delete a column after
                 * having already decided to drop its whole table.  Obviously
                 * we no longer need to drop the subobject, so report that we
                 * found the subobject in the array.  But don't plaster its
                 * flags on the whole object.
                 */
                result = true;
            }
            else if (object->objectSubId == 0)
            {
                /*
                 * We get here if we find a need to delete a whole table after
                 * having already decided to drop one of its columns.  We
                 * can't report that the whole object is in the array, but we
                 * should mark the subobject with the whole object's flags.
                 *
                 * It might seem attractive to physically delete the column's
                 * array entry, or at least mark it as no longer needing
                 * separate deletion.  But that could lead to, e.g., dropping
                 * the column's datatype before we drop the table, which does
                 * not seem like a good idea.  This is a very rare situation
                 * in practice, so we just take the hit of doing a separate
                 * DROP COLUMN action even though we know we're gonna delete
                 * the table later.
                 *
                 * Because there could be other subobjects of this object in
                 * the array, this case means we always have to loop through
                 * the whole array; we cannot exit early on a match.
                 */
                ObjectAddressExtra *thisextra = addrs->extras + i;

                thisextra->flags |= flags;
            }
        }
    }

    return result;
}

/*
 * Similar to above, except we search an ObjectAddressStack.
 */
static bool
stack_address_present_add_flags(const ObjectAddress *object,
                                int flags,
                                ObjectAddressStack *stack)
{
    bool        result = false;
    ObjectAddressStack *stackptr;

    for (stackptr = stack; stackptr; stackptr = stackptr->next)
    {
        const ObjectAddress *thisobj = stackptr->object;

        if (object->classId == thisobj->classId &&
            object->objectId == thisobj->objectId)
        {
            if (object->objectSubId == thisobj->objectSubId)
            {
                stackptr->flags |= flags;
                result = true;
            }
            else if (thisobj->objectSubId == 0)
            {
                /*
                 * We're visiting a column with whole table already on stack.
                 * As in object_address_present_add_flags(), we can skip
                 * further processing of the subobject, but we don't want to
                 * propagate flags for the subobject to the whole object.
                 */
                result = true;
            }
            else if (object->objectSubId == 0)
            {
                /*
                 * We're visiting a table with column already on stack.  As in
                 * object_address_present_add_flags(), we should propagate
                 * flags for the whole object to each of its subobjects.
                 */
                stackptr->flags |= flags;
            }
        }
    }

    return result;
}

/*
 * Record multiple dependencies from an ObjectAddresses array, after first
 * removing any duplicates.
 */
void
record_object_address_dependencies(const ObjectAddress *depender,
                                   ObjectAddresses *referenced,
                                   DependencyType behavior)
{
    eliminate_duplicate_dependencies(referenced);
    recordMultipleDependencies(depender,
                               referenced->refs, referenced->numrefs,
                               behavior);
}

/*
 * Clean up when done with an ObjectAddresses array.
 */
void
free_object_addresses(ObjectAddresses *addrs)
{
    pfree(addrs->refs);
    if (addrs->extras)
        pfree(addrs->extras);
    pfree(addrs);
}

/*
 * Determine the class of a given object identified by objectAddress.
 *
 * This function is essentially the reverse mapping for the object_classes[]
 * table.  We implement it as a function because the OIDs aren't consecutive.
 */
ObjectClass
getObjectClass(const ObjectAddress *object)
{
    /* only pg_class entries can have nonzero objectSubId */
    if (object->classId != RelationRelationId &&
        object->objectSubId != 0)
        elog(ERROR, "invalid non-zero objectSubId for object class %u",
             object->classId);

    switch (object->classId)
    {
        case RelationRelationId:
            /* caller must check objectSubId */
            return OCLASS_CLASS;

        case ProcedureRelationId:
            return OCLASS_PROC;

        case TypeRelationId:
            return OCLASS_TYPE;

        case CastRelationId:
            return OCLASS_CAST;

        case CollationRelationId:
            return OCLASS_COLLATION;

        case ConstraintRelationId:
            return OCLASS_CONSTRAINT;

        case ConversionRelationId:
            return OCLASS_CONVERSION;

        case AttrDefaultRelationId:
            return OCLASS_DEFAULT;

        case LanguageRelationId:
            return OCLASS_LANGUAGE;

        case LargeObjectRelationId:
            return OCLASS_LARGEOBJECT;

        case OperatorRelationId:
            return OCLASS_OPERATOR;

        case OperatorClassRelationId:
            return OCLASS_OPCLASS;

        case OperatorFamilyRelationId:
            return OCLASS_OPFAMILY;

        case AccessMethodRelationId:
            return OCLASS_AM;

        case AccessMethodOperatorRelationId:
            return OCLASS_AMOP;

        case AccessMethodProcedureRelationId:
            return OCLASS_AMPROC;

        case RewriteRelationId:
            return OCLASS_REWRITE;

        case TriggerRelationId:
            return OCLASS_TRIGGER;

        case NamespaceRelationId:
            return OCLASS_SCHEMA;

        case StatisticExtRelationId:
            return OCLASS_STATISTIC_EXT;

        case TSParserRelationId:
            return OCLASS_TSPARSER;

        case TSDictionaryRelationId:
            return OCLASS_TSDICT;

        case TSTemplateRelationId:
            return OCLASS_TSTEMPLATE;

        case TSConfigRelationId:
            return OCLASS_TSCONFIG;

        case AuthIdRelationId:
            return OCLASS_ROLE;

        case DatabaseRelationId:
            return OCLASS_DATABASE;

        case TableSpaceRelationId:
            return OCLASS_TBLSPACE;

        case ForeignDataWrapperRelationId:
            return OCLASS_FDW;

        case ForeignServerRelationId:
            return OCLASS_FOREIGN_SERVER;

        case UserMappingRelationId:
            return OCLASS_USER_MAPPING;

        case DefaultAclRelationId:
            return OCLASS_DEFACL;

        case ExtensionRelationId:
            return OCLASS_EXTENSION;

        case EventTriggerRelationId:
            return OCLASS_EVENT_TRIGGER;

        case PolicyRelationId:
            return OCLASS_POLICY;

        case PublicationRelationId:
            return OCLASS_PUBLICATION;

        case PublicationRelRelationId:
            return OCLASS_PUBLICATION_REL;

        case SubscriptionRelationId:
            return OCLASS_SUBSCRIPTION;

        case TransformRelationId:
            return OCLASS_TRANSFORM;
    }

    /* shouldn't get here */
    elog(ERROR, "unrecognized object class: %u", object->classId);
    return OCLASS_CLASS;        /* keep compiler quiet */
}

/*
 * delete initial ACL for extension objects
 */
static void
DeleteInitPrivs(const ObjectAddress *object)
{
    Relation    relation;
    ScanKeyData key[3];
    SysScanDesc scan;
    HeapTuple   oldtuple;

    relation = heap_open(InitPrivsRelationId, RowExclusiveLock);

    ScanKeyInit(&key[0],
                Anum_pg_init_privs_objoid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(object->objectId));
    ScanKeyInit(&key[1],
                Anum_pg_init_privs_classoid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(object->classId));
    ScanKeyInit(&key[2],
                Anum_pg_init_privs_objsubid,
                BTEqualStrategyNumber, F_INT4EQ,
                Int32GetDatum(object->objectSubId));

    scan = systable_beginscan(relation, InitPrivsObjIndexId, true,
                              NULL, 3, key);

    while (HeapTupleIsValid(oldtuple = systable_getnext(scan)))
        CatalogTupleDelete(relation, &oldtuple->t_self);

    systable_endscan(scan);

    heap_close(relation, RowExclusiveLock);
}