1 files changed, 78 insertions, 0 deletions
diff --git a/src/backend/commands/discard.c b/src/backend/commands/discard.c
new file mode 100644
index 0000000..57d3d7d
--- /dev/null
+++ b/src/backend/commands/discard.c
@@ -0,0 +1,78 @@
+/*-------------------------------------------------------------------------
+ *
+ * discard.c
+ *	  The implementation of the DISCARD command
+ *
+ * Copyright (c) 1996-2021, 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"
+
+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();
+}