discard.c

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/*-------------------------------------------------------------------------
 *
 * discard.c
 *    The implementation of the DISCARD command
 *
 * Copyright (c) 1996-2026, PostgreSQL Global Development Group
 *
 *
 * IDENTIFICATION
 *    src/backend/commands/discard.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include "access/xact.h"
#include "catalog/namespace.h"
#include "commands/async.h"
#include "commands/discard.h"
#include "commands/prepare.h"
#include "commands/sequence.h"
#include "storage/lock.h"
#include "utils/guc.h"
#include "utils/portal.h"
 
static void DiscardAll(bool isTopLevel);
 
/*
 * DISCARD { ALL | SEQUENCES | TEMP | PLANS }
 */
void
DiscardCommand(DiscardStmt *stmt, bool isTopLevel)
{
    switch (stmt->target)
    {
        case DISCARD_ALL:
            DiscardAll(isTopLevel);
            break;
 
        case DISCARD_PLANS:
            ResetPlanCache();
            break;
 
        case DISCARD_SEQUENCES:
            ResetSequenceCaches();
            break;
 
        case DISCARD_TEMP:
            ResetTempTableNamespace();
            break;
 
        default:
            elog(ERROR, "unrecognized DISCARD target: %d", stmt->target);
    }
}
 
static void
DiscardAll(bool isTopLevel)
{
    /*
     * Disallow DISCARD ALL in a transaction block. This is arguably
     * inconsistent (we don't make a similar check in the command sequence
     * that DISCARD ALL is equivalent to), but the idea is to catch mistakes:
     * DISCARD ALL inside a transaction block would leave the transaction
     * still uncommitted.
     */
    PreventInTransactionBlock(isTopLevel, "DISCARD ALL");
 
    /* Closing portals might run user-defined code, so do that first. */
    PortalHashTableDeleteAll();
    SetPGVariable("session_authorization", NIL, false);
    ResetAllOptions();
    DropAllPreparedStatements();
    Async_UnlistenAll();
    LockReleaseAll(USER_LOCKMETHOD, true);
    ResetPlanCache();
    ResetTempTableNamespace();
    ResetSequenceCaches();
}