rewriteDefine.c

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/*-------------------------------------------------------------------------
 *
 * rewriteDefine.c
 *    routines for defining a rewrite rule
 *
 * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/rewrite/rewriteDefine.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include "access/heapam.h"
#include "access/htup_details.h"
#include "access/multixact.h"
#include "access/tableam.h"
#include "access/transam.h"
#include "access/xact.h"
#include "catalog/catalog.h"
#include "catalog/dependency.h"
#include "catalog/heap.h"
#include "catalog/namespace.h"
#include "catalog/objectaccess.h"
#include "catalog/pg_inherits.h"
#include "catalog/pg_rewrite.h"
#include "catalog/storage.h"
#include "commands/policy.h"
#include "miscadmin.h"
#include "nodes/nodeFuncs.h"
#include "parser/parse_utilcmd.h"
#include "rewrite/rewriteDefine.h"
#include "rewrite/rewriteManip.h"
#include "rewrite/rewriteSupport.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/inval.h"
#include "utils/lsyscache.h"
#include "utils/rel.h"
#include "utils/snapmgr.h"
#include "utils/syscache.h"
 
 
static void checkRuleResultList(List *targetList, TupleDesc resultDesc,
                                bool isSelect, bool requireColumnNameMatch);
static bool setRuleCheckAsUser_walker(Node *node, Oid *context);
static void setRuleCheckAsUser_Query(Query *qry, Oid userid);
 
 
/*
 * InsertRule -
 *    takes the arguments and inserts them as a row into the system
 *    relation "pg_rewrite"
 */
static Oid
InsertRule(const char *rulname,
           int evtype,
           Oid eventrel_oid,
           bool evinstead,
           Node *event_qual,
           List *action,
           bool replace)
{
    char       *evqual = nodeToString(event_qual);
    char       *actiontree = nodeToString((Node *) action);
    Datum       values[Natts_pg_rewrite];
    bool        nulls[Natts_pg_rewrite] = {0};
    NameData    rname;
    Relation    pg_rewrite_desc;
    HeapTuple   tup,
                oldtup;
    Oid         rewriteObjectId;
    ObjectAddress myself,
                referenced;
    bool        is_update = false;
 
    /*
     * Set up *nulls and *values arrays
     */
    namestrcpy(&rname, rulname);
    values[Anum_pg_rewrite_rulename - 1] = NameGetDatum(&rname);
    values[Anum_pg_rewrite_ev_class - 1] = ObjectIdGetDatum(eventrel_oid);
    values[Anum_pg_rewrite_ev_type - 1] = CharGetDatum(evtype + '0');
    values[Anum_pg_rewrite_ev_enabled - 1] = CharGetDatum(RULE_FIRES_ON_ORIGIN);
    values[Anum_pg_rewrite_is_instead - 1] = BoolGetDatum(evinstead);
    values[Anum_pg_rewrite_ev_qual - 1] = CStringGetTextDatum(evqual);
    values[Anum_pg_rewrite_ev_action - 1] = CStringGetTextDatum(actiontree);
 
    /*
     * Ready to store new pg_rewrite tuple
     */
    pg_rewrite_desc = table_open(RewriteRelationId, RowExclusiveLock);
 
    /*
     * Check to see if we are replacing an existing tuple
     */
    oldtup = SearchSysCache2(RULERELNAME,
                             ObjectIdGetDatum(eventrel_oid),
                             PointerGetDatum(rulname));
 
    if (HeapTupleIsValid(oldtup))
    {
        bool        replaces[Natts_pg_rewrite] = {0};
 
        if (!replace)
            ereport(ERROR,
                    (errcode(ERRCODE_DUPLICATE_OBJECT),
                     errmsg("rule \"%s\" for relation \"%s\" already exists",
                            rulname, get_rel_name(eventrel_oid))));
 
        /*
         * When replacing, we don't need to replace every attribute
         */
        replaces[Anum_pg_rewrite_ev_type - 1] = true;
        replaces[Anum_pg_rewrite_is_instead - 1] = true;
        replaces[Anum_pg_rewrite_ev_qual - 1] = true;
        replaces[Anum_pg_rewrite_ev_action - 1] = true;
 
        tup = heap_modify_tuple(oldtup, RelationGetDescr(pg_rewrite_desc),
                                values, nulls, replaces);
 
        CatalogTupleUpdate(pg_rewrite_desc, &tup->t_self, tup);
 
        ReleaseSysCache(oldtup);
 
        rewriteObjectId = ((Form_pg_rewrite) GETSTRUCT(tup))->oid;
        is_update = true;
    }
    else
    {
        rewriteObjectId = GetNewOidWithIndex(pg_rewrite_desc,
                                             RewriteOidIndexId,
                                             Anum_pg_rewrite_oid);
        values[Anum_pg_rewrite_oid - 1] = ObjectIdGetDatum(rewriteObjectId);
 
        tup = heap_form_tuple(pg_rewrite_desc->rd_att, values, nulls);
 
        CatalogTupleInsert(pg_rewrite_desc, tup);
    }
 
 
    heap_freetuple(tup);
 
    /* If replacing, get rid of old dependencies and make new ones */
    if (is_update)
        deleteDependencyRecordsFor(RewriteRelationId, rewriteObjectId, false);
 
    /*
     * Install dependency on rule's relation to ensure it will go away on
     * relation deletion.  If the rule is ON SELECT, make the dependency
     * implicit --- this prevents deleting a view's SELECT rule.  Other kinds
     * of rules can be AUTO.
     */
    myself.classId = RewriteRelationId;
    myself.objectId = rewriteObjectId;
    myself.objectSubId = 0;
 
    referenced.classId = RelationRelationId;
    referenced.objectId = eventrel_oid;
    referenced.objectSubId = 0;
 
    recordDependencyOn(&myself, &referenced,
                       (evtype == CMD_SELECT) ? DEPENDENCY_INTERNAL : DEPENDENCY_AUTO);
 
    /*
     * Also install dependencies on objects referenced in action and qual.
     */
    recordDependencyOnExpr(&myself, (Node *) action, NIL,
                           DEPENDENCY_NORMAL);
 
    if (event_qual != NULL)
    {
        /* Find query containing OLD/NEW rtable entries */
        Query      *qry = linitial_node(Query, action);
 
        qry = getInsertSelectQuery(qry, NULL);
        recordDependencyOnExpr(&myself, event_qual, qry->rtable,
                               DEPENDENCY_NORMAL);
    }
 
    /* Post creation hook for new rule */
    InvokeObjectPostCreateHook(RewriteRelationId, rewriteObjectId, 0);
 
    table_close(pg_rewrite_desc, RowExclusiveLock);
 
    return rewriteObjectId;
}
 
/*
 * DefineRule
 *      Execute a CREATE RULE command.
 */
ObjectAddress
DefineRule(RuleStmt *stmt, const char *queryString)
{
    List       *actions;
    Node       *whereClause;
    Oid         relId;
 
    /* Parse analysis. */
    transformRuleStmt(stmt, queryString, &actions, &whereClause);
 
    /*
     * Find and lock the relation.  Lock level should match
     * DefineQueryRewrite.
     */
    relId = RangeVarGetRelid(stmt->relation, AccessExclusiveLock, false);
 
    /* ... and execute */
    return DefineQueryRewrite(stmt->rulename,
                              relId,
                              whereClause,
                              stmt->event,
                              stmt->instead,
                              stmt->replace,
                              actions);
}
 
 
/*
 * DefineQueryRewrite
 *      Create a rule
 *
 * This is essentially the same as DefineRule() except that the rule's
 * action and qual have already been passed through parse analysis.
 */
ObjectAddress
DefineQueryRewrite(const char *rulename,
                   Oid event_relid,
                   Node *event_qual,
                   CmdType event_type,
                   bool is_instead,
                   bool replace,
                   List *action)
{
    Relation    event_relation;
    ListCell   *l;
    Query      *query;
    Oid         ruleId = InvalidOid;
    ObjectAddress address;
 
    /*
     * If we are installing an ON SELECT rule, we had better grab
     * AccessExclusiveLock to ensure no SELECTs are currently running on the
     * event relation. For other types of rules, it would be sufficient to
     * grab ShareRowExclusiveLock to lock out insert/update/delete actions and
     * to ensure that we lock out current CREATE RULE statements; but because
     * of race conditions in access to catalog entries, we can't do that yet.
     *
     * Note that this lock level should match the one used in DefineRule.
     */
    event_relation = table_open(event_relid, AccessExclusiveLock);
 
    /*
     * Verify relation is of a type that rules can sensibly be applied to.
     * Internal callers can target materialized views, but transformRuleStmt()
     * blocks them for users.  Don't mention them in the error message.
     */
    if (event_relation->rd_rel->relkind != RELKIND_RELATION &&
        event_relation->rd_rel->relkind != RELKIND_MATVIEW &&
        event_relation->rd_rel->relkind != RELKIND_VIEW &&
        event_relation->rd_rel->relkind != RELKIND_PARTITIONED_TABLE)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("relation \"%s\" cannot have rules",
                        RelationGetRelationName(event_relation)),
                 errdetail_relkind_not_supported(event_relation->rd_rel->relkind)));
 
    if (!allowSystemTableMods && IsSystemRelation(event_relation))
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("permission denied: \"%s\" is a system catalog",
                        RelationGetRelationName(event_relation))));
 
    /*
     * Check user has permission to apply rules to this relation.
     */
    if (!object_ownercheck(RelationRelationId, event_relid, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, get_relkind_objtype(event_relation->rd_rel->relkind),
                       RelationGetRelationName(event_relation));
 
    /*
     * No rule actions that modify OLD or NEW
     */
    foreach(l, action)
    {
        query = lfirst_node(Query, l);
        if (query->resultRelation == 0)
            continue;
        /* Don't be fooled by INSERT/SELECT */
        if (query != getInsertSelectQuery(query, NULL))
            continue;
        if (query->resultRelation == PRS2_OLD_VARNO)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("rule actions on OLD are not implemented"),
                     errhint("Use views or triggers instead.")));
        if (query->resultRelation == PRS2_NEW_VARNO)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("rule actions on NEW are not implemented"),
                     errhint("Use triggers instead.")));
    }
 
    if (event_type == CMD_SELECT)
    {
        /*
         * Rules ON SELECT are restricted to view definitions
         *
         * So this had better be a view, ...
         */
        if (event_relation->rd_rel->relkind != RELKIND_VIEW &&
            event_relation->rd_rel->relkind != RELKIND_MATVIEW)
            ereport(ERROR,
                    (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                     errmsg("relation \"%s\" cannot have ON SELECT rules",
                            RelationGetRelationName(event_relation)),
                     errdetail_relkind_not_supported(event_relation->rd_rel->relkind)));
 
        /*
         * ... there cannot be INSTEAD NOTHING, ...
         */
        if (action == NIL)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("INSTEAD NOTHING rules on SELECT are not implemented"),
                     errhint("Use views instead.")));
 
        /*
         * ... there cannot be multiple actions, ...
         */
        if (list_length(action) > 1)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("multiple actions for rules on SELECT are not implemented")));
 
        /*
         * ... the one action must be a SELECT, ...
         */
        query = linitial_node(Query, action);
        if (!is_instead ||
            query->commandType != CMD_SELECT)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("rules on SELECT must have action INSTEAD SELECT")));
 
        /*
         * ... it cannot contain data-modifying WITH ...
         */
        if (query->hasModifyingCTE)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("rules on SELECT must not contain data-modifying statements in WITH")));
 
        /*
         * ... there can be no rule qual, ...
         */
        if (event_qual != NULL)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("event qualifications are not implemented for rules on SELECT")));
 
        /*
         * ... the targetlist of the SELECT action must exactly match the
         * event relation, ...
         */
        checkRuleResultList(query->targetList,
                            RelationGetDescr(event_relation),
                            true,
                            event_relation->rd_rel->relkind !=
                            RELKIND_MATVIEW);
 
        /*
         * ... there must not be another ON SELECT rule already ...
         */
        if (!replace && event_relation->rd_rules != NULL)
        {
            int         i;
 
            for (i = 0; i < event_relation->rd_rules->numLocks; i++)
            {
                RewriteRule *rule;
 
                rule = event_relation->rd_rules->rules[i];
                if (rule->event == CMD_SELECT)
                    ereport(ERROR,
                            (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                             errmsg("\"%s\" is already a view",
                                    RelationGetRelationName(event_relation))));
            }
        }
 
        /*
         * ... and finally the rule must be named _RETURN.
         */
        if (strcmp(rulename, ViewSelectRuleName) != 0)
        {
            /*
             * In versions before 7.3, the expected name was _RETviewname. For
             * backwards compatibility with old pg_dump output, accept that
             * and silently change it to _RETURN.  Since this is just a quick
             * backwards-compatibility hack, limit the number of characters
             * checked to a few less than NAMEDATALEN; this saves having to
             * worry about where a multibyte character might have gotten
             * truncated.
             */
            if (strncmp(rulename, "_RET", 4) != 0 ||
                strncmp(rulename + 4, RelationGetRelationName(event_relation),
                        NAMEDATALEN - 4 - 4) != 0)
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                         errmsg("view rule for \"%s\" must be named \"%s\"",
                                RelationGetRelationName(event_relation),
                                ViewSelectRuleName)));
            rulename = pstrdup(ViewSelectRuleName);
        }
    }
    else
    {
        /*
         * For non-SELECT rules, a RETURNING list can appear in at most one of
         * the actions ... and there can't be any RETURNING list at all in a
         * conditional or non-INSTEAD rule.  (Actually, there can be at most
         * one RETURNING list across all rules on the same event, but it seems
         * best to enforce that at rule expansion time.)  If there is a
         * RETURNING list, it must match the event relation.
         */
        bool        haveReturning = false;
 
        foreach(l, action)
        {
            query = lfirst_node(Query, l);
 
            if (!query->returningList)
                continue;
            if (haveReturning)
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("cannot have multiple RETURNING lists in a rule")));
            haveReturning = true;
            if (event_qual != NULL)
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("RETURNING lists are not supported in conditional rules")));
            if (!is_instead)
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("RETURNING lists are not supported in non-INSTEAD rules")));
            checkRuleResultList(query->returningList,
                                RelationGetDescr(event_relation),
                                false, false);
        }
 
        /*
         * And finally, if it's not an ON SELECT rule then it must *not* be
         * named _RETURN.  This prevents accidentally or maliciously replacing
         * a view's ON SELECT rule with some other kind of rule.
         */
        if (strcmp(rulename, ViewSelectRuleName) == 0)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                     errmsg("non-view rule for \"%s\" must not be named \"%s\"",
                            RelationGetRelationName(event_relation),
                            ViewSelectRuleName)));
    }
 
    /*
     * This rule is allowed - prepare to install it.
     */
 
    /* discard rule if it's null action and not INSTEAD; it's a no-op */
    if (action != NIL || is_instead)
    {
        ruleId = InsertRule(rulename,
                            event_type,
                            event_relid,
                            is_instead,
                            event_qual,
                            action,
                            replace);
 
        /*
         * Set pg_class 'relhasrules' field true for event relation.
         *
         * Important side effect: an SI notice is broadcast to force all
         * backends (including me!) to update relcache entries with the new
         * rule.
         */
        SetRelationRuleStatus(event_relid, true);
    }
 
    ObjectAddressSet(address, RewriteRelationId, ruleId);
 
    /* Close rel, but keep lock till commit... */
    table_close(event_relation, NoLock);
 
    return address;
}
 
/*
 * checkRuleResultList
 *      Verify that targetList produces output compatible with a tupledesc
 *
 * The targetList might be either a SELECT targetlist, or a RETURNING list;
 * isSelect tells which.  This is used for choosing error messages.
 *
 * A SELECT targetlist may optionally require that column names match.
 */
static void
checkRuleResultList(List *targetList, TupleDesc resultDesc, bool isSelect,
                    bool requireColumnNameMatch)
{
    ListCell   *tllist;
    int         i;
 
    /* Only a SELECT may require a column name match. */
    Assert(isSelect || !requireColumnNameMatch);
 
    i = 0;
    foreach(tllist, targetList)
    {
        TargetEntry *tle = (TargetEntry *) lfirst(tllist);
        Oid         tletypid;
        int32       tletypmod;
        Form_pg_attribute attr;
        char       *attname;
 
        /* resjunk entries may be ignored */
        if (tle->resjunk)
            continue;
        i++;
        if (i > resultDesc->natts)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                     isSelect ?
                     errmsg("SELECT rule's target list has too many entries") :
                     errmsg("RETURNING list has too many entries")));
 
        attr = TupleDescAttr(resultDesc, i - 1);
        attname = NameStr(attr->attname);
 
        /*
         * Disallow dropped columns in the relation.  This is not really
         * expected to happen when creating an ON SELECT rule.  It'd be
         * possible if someone tried to convert a relation with dropped
         * columns to a view, but the only case we care about supporting
         * table-to-view conversion for is pg_dump, and pg_dump won't do that.
         *
         * Unfortunately, the situation is also possible when adding a rule
         * with RETURNING to a regular table, and rejecting that case is
         * altogether more annoying.  In principle we could support it by
         * modifying the targetlist to include dummy NULL columns
         * corresponding to the dropped columns in the tupdesc.  However,
         * places like ruleutils.c would have to be fixed to not process such
         * entries, and that would take an uncertain and possibly rather large
         * amount of work.  (Note we could not dodge that by marking the dummy
         * columns resjunk, since it's precisely the non-resjunk tlist columns
         * that are expected to correspond to table columns.)
         */
        if (attr->attisdropped)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     isSelect ?
                     errmsg("cannot convert relation containing dropped columns to view") :
                     errmsg("cannot create a RETURNING list for a relation containing dropped columns")));
 
        /* Check name match if required; no need for two error texts here */
        if (requireColumnNameMatch && strcmp(tle->resname, attname) != 0)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                     errmsg("SELECT rule's target entry %d has different column name from column \"%s\"",
                            i, attname),
                     errdetail("SELECT target entry is named \"%s\".",
                               tle->resname)));
 
        /* Check type match. */
        tletypid = exprType((Node *) tle->expr);
        if (attr->atttypid != tletypid)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                     isSelect ?
                     errmsg("SELECT rule's target entry %d has different type from column \"%s\"",
                            i, attname) :
                     errmsg("RETURNING list's entry %d has different type from column \"%s\"",
                            i, attname),
                     isSelect ?
                     errdetail("SELECT target entry has type %s, but column has type %s.",
                               format_type_be(tletypid),
                               format_type_be(attr->atttypid)) :
                     errdetail("RETURNING list entry has type %s, but column has type %s.",
                               format_type_be(tletypid),
                               format_type_be(attr->atttypid))));
 
        /*
         * Allow typmods to be different only if one of them is -1, ie,
         * "unspecified".  This is necessary for cases like "numeric", where
         * the table will have a filled-in default length but the select
         * rule's expression will probably have typmod = -1.
         */
        tletypmod = exprTypmod((Node *) tle->expr);
        if (attr->atttypmod != tletypmod &&
            attr->atttypmod != -1 && tletypmod != -1)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                     isSelect ?
                     errmsg("SELECT rule's target entry %d has different size from column \"%s\"",
                            i, attname) :
                     errmsg("RETURNING list's entry %d has different size from column \"%s\"",
                            i, attname),
                     isSelect ?
                     errdetail("SELECT target entry has type %s, but column has type %s.",
                               format_type_with_typemod(tletypid, tletypmod),
                               format_type_with_typemod(attr->atttypid,
                                                        attr->atttypmod)) :
                     errdetail("RETURNING list entry has type %s, but column has type %s.",
                               format_type_with_typemod(tletypid, tletypmod),
                               format_type_with_typemod(attr->atttypid,
                                                        attr->atttypmod))));
    }
 
    if (i != resultDesc->natts)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                 isSelect ?
                 errmsg("SELECT rule's target list has too few entries") :
                 errmsg("RETURNING list has too few entries")));
}
 
/*
 * setRuleCheckAsUser
 *      Recursively scan a query or expression tree and set the checkAsUser
 *      field to the given userid in all RTEPermissionInfos of the query.
 */
void
setRuleCheckAsUser(Node *node, Oid userid)
{
    (void) setRuleCheckAsUser_walker(node, &userid);
}
 
static bool
setRuleCheckAsUser_walker(Node *node, Oid *context)
{
    if (node == NULL)
        return false;
    if (IsA(node, Query))
    {
        setRuleCheckAsUser_Query((Query *) node, *context);
        return false;
    }
    return expression_tree_walker(node, setRuleCheckAsUser_walker,
                                  (void *) context);
}
 
static void
setRuleCheckAsUser_Query(Query *qry, Oid userid)
{
    ListCell   *l;
 
    /* Set in all RTEPermissionInfos for this query. */
    foreach(l, qry->rteperminfos)
    {
        RTEPermissionInfo *perminfo = lfirst_node(RTEPermissionInfo, l);
 
        perminfo->checkAsUser = userid;
    }
 
    /* Now recurse to any subquery RTEs */
    foreach(l, qry->rtable)
    {
        RangeTblEntry *rte = (RangeTblEntry *) lfirst(l);
 
        if (rte->rtekind == RTE_SUBQUERY)
            setRuleCheckAsUser_Query(rte->subquery, userid);
    }
 
    /* Recurse into subquery-in-WITH */
    foreach(l, qry->cteList)
    {
        CommonTableExpr *cte = (CommonTableExpr *) lfirst(l);
 
        setRuleCheckAsUser_Query(castNode(Query, cte->ctequery), userid);
    }
 
    /* If there are sublinks, search for them and process their RTEs */
    if (qry->hasSubLinks)
        query_tree_walker(qry, setRuleCheckAsUser_walker, (void *) &userid,
                          QTW_IGNORE_RC_SUBQUERIES);
}
 
 
/*
 * Change the firing semantics of an existing rule.
 */
void
EnableDisableRule(Relation rel, const char *rulename,
                  char fires_when)
{
    Relation    pg_rewrite_desc;
    Oid         owningRel = RelationGetRelid(rel);
    Oid         eventRelationOid;
    HeapTuple   ruletup;
    Form_pg_rewrite ruleform;
    bool        changed = false;
 
    /*
     * Find the rule tuple to change.
     */
    pg_rewrite_desc = table_open(RewriteRelationId, RowExclusiveLock);
    ruletup = SearchSysCacheCopy2(RULERELNAME,
                                  ObjectIdGetDatum(owningRel),
                                  PointerGetDatum(rulename));
    if (!HeapTupleIsValid(ruletup))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("rule \"%s\" for relation \"%s\" does not exist",
                        rulename, get_rel_name(owningRel))));
 
    ruleform = (Form_pg_rewrite) GETSTRUCT(ruletup);
 
    /*
     * Verify that the user has appropriate permissions.
     */
    eventRelationOid = ruleform->ev_class;
    Assert(eventRelationOid == owningRel);
    if (!object_ownercheck(RelationRelationId, eventRelationOid, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, get_relkind_objtype(get_rel_relkind(eventRelationOid)),
                       get_rel_name(eventRelationOid));
 
    /*
     * Change ev_enabled if it is different from the desired new state.
     */
    if (DatumGetChar(ruleform->ev_enabled) !=
        fires_when)
    {
        ruleform->ev_enabled = CharGetDatum(fires_when);
        CatalogTupleUpdate(pg_rewrite_desc, &ruletup->t_self, ruletup);
 
        changed = true;
    }
 
    InvokeObjectPostAlterHook(RewriteRelationId, ruleform->oid, 0);
 
    heap_freetuple(ruletup);
    table_close(pg_rewrite_desc, RowExclusiveLock);
 
    /*
     * If we changed anything, broadcast a SI inval message to force each
     * backend (including our own!) to rebuild relation's relcache entry.
     * Otherwise they will fail to apply the change promptly.
     */
    if (changed)
        CacheInvalidateRelcache(rel);
}
 
 
/*
 * Perform permissions and integrity checks before acquiring a relation lock.
 */
static void
RangeVarCallbackForRenameRule(const RangeVar *rv, Oid relid, Oid oldrelid,
                              void *arg)
{
    HeapTuple   tuple;
    Form_pg_class form;
 
    tuple = SearchSysCache1(RELOID, ObjectIdGetDatum(relid));
    if (!HeapTupleIsValid(tuple))
        return;                 /* concurrently dropped */
    form = (Form_pg_class) GETSTRUCT(tuple);
 
    /* only tables and views can have rules */
    if (form->relkind != RELKIND_RELATION &&
        form->relkind != RELKIND_VIEW &&
        form->relkind != RELKIND_PARTITIONED_TABLE)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("relation \"%s\" cannot have rules", rv->relname),
                 errdetail_relkind_not_supported(form->relkind)));
 
    if (!allowSystemTableMods && IsSystemClass(relid, form))
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("permission denied: \"%s\" is a system catalog",
                        rv->relname)));
 
    /* you must own the table to rename one of its rules */
    if (!object_ownercheck(RelationRelationId, relid, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, get_relkind_objtype(get_rel_relkind(relid)), rv->relname);
 
    ReleaseSysCache(tuple);
}
 
/*
 * Rename an existing rewrite rule.
 */
ObjectAddress
RenameRewriteRule(RangeVar *relation, const char *oldName,
                  const char *newName)
{
    Oid         relid;
    Relation    targetrel;
    Relation    pg_rewrite_desc;
    HeapTuple   ruletup;
    Form_pg_rewrite ruleform;
    Oid         ruleOid;
    ObjectAddress address;
 
    /*
     * Look up name, check permissions, and acquire lock (which we will NOT
     * release until end of transaction).
     */
    relid = RangeVarGetRelidExtended(relation, AccessExclusiveLock,
                                     0,
                                     RangeVarCallbackForRenameRule,
                                     NULL);
 
    /* Have lock already, so just need to build relcache entry. */
    targetrel = relation_open(relid, NoLock);
 
    /* Prepare to modify pg_rewrite */
    pg_rewrite_desc = table_open(RewriteRelationId, RowExclusiveLock);
 
    /* Fetch the rule's entry (it had better exist) */
    ruletup = SearchSysCacheCopy2(RULERELNAME,
                                  ObjectIdGetDatum(relid),
                                  PointerGetDatum(oldName));
    if (!HeapTupleIsValid(ruletup))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("rule \"%s\" for relation \"%s\" does not exist",
                        oldName, RelationGetRelationName(targetrel))));
    ruleform = (Form_pg_rewrite) GETSTRUCT(ruletup);
    ruleOid = ruleform->oid;
 
    /* rule with the new name should not already exist */
    if (IsDefinedRewriteRule(relid, newName))
        ereport(ERROR,
                (errcode(ERRCODE_DUPLICATE_OBJECT),
                 errmsg("rule \"%s\" for relation \"%s\" already exists",
                        newName, RelationGetRelationName(targetrel))));
 
    /*
     * We disallow renaming ON SELECT rules, because they should always be
     * named "_RETURN".
     */
    if (ruleform->ev_type == CMD_SELECT + '0')
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                 errmsg("renaming an ON SELECT rule is not allowed")));
 
    /* OK, do the update */
    namestrcpy(&(ruleform->rulename), newName);
 
    CatalogTupleUpdate(pg_rewrite_desc, &ruletup->t_self, ruletup);
 
    InvokeObjectPostAlterHook(RewriteRelationId, ruleOid, 0);
 
    heap_freetuple(ruletup);
    table_close(pg_rewrite_desc, RowExclusiveLock);
 
    /*
     * Invalidate relation's relcache entry so that other backends (and this
     * one too!) are sent SI message to make them rebuild relcache entries.
     * (Ideally this should happen automatically...)
     */
    CacheInvalidateRelcache(targetrel);
 
    ObjectAddressSet(address, RewriteRelationId, ruleOid);
 
    /*
     * Close rel, but keep exclusive lock!
     */
    relation_close(targetrel, NoLock);
 
    return address;
}