greenplumn discard 源码
greenplumn discard 代码
文件路径：/src/backend/commands/discard.c
/*-------------------------------------------------------------------------
*
* discard.c
* The implementation of the DISCARD command
*
* Copyright (c) 1996-2019, 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 "utils/guc.h"
#include "utils/portal.h"
#include "cdb/cdbdisp_query.h"
#include "cdb/cdbgang.h"
#include "cdb/cdbvars.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);
/*
* DISCARD ALL is not allowed in a transaction block. It is not
* currently possible to safeguard from side-effecs of errors.
*
* Do not dispatch.
*/
break;
case DISCARD_PLANS:
ResetPlanCache();
/* no dispatch, there should be no cached plans in segments */
break;
case DISCARD_SEQUENCES:
ResetSequenceCaches();
/* no dispatch, there should be no sequence caches in segments */
break;
case DISCARD_TEMP:
ResetTempTableNamespace();
/*
* Dispatch using two-phase commit, so that the effect of DISCARD
* TEMP can be rolled back if it's run in a transaction.
*/
if (Gp_role == GP_ROLE_DISPATCH)
CdbDispatchCommand("DISCARD TEMP", DF_NEED_TWO_PHASE, NULL);
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");
/*
* GPDB: It is not possible to safely dispatch DISCARD ALL and safe guard
* from errors. Advice users (very frequently connection pooling
* applications e.g. pgbouncer) to use a lighter and safer version e.g.
* DEALLOCATE ALL, or DISCARD TEMP
*
*/
if (Gp_role == GP_ROLE_DISPATCH)
{
ereport(NOTICE,
(errcode(ERRCODE_GP_FEATURE_NOT_YET),
errmsg("command without clusterwide effect"),
errhint("Consider alternatives as DEALLOCATE ALL, or DISCARD TEMP if a clusterwide effect is desired.")));
}
/* 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();
}
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