Add DISCARD SEQUENCES command.

DISCARD ALL will now discard cached sequence information, as well.

Fabrízio de Royes Mello, reviewed by Zoltán Böszörményi, with some
further tweaks by me.

doc/src/sgml/ref/discard.sgml

@@ -21,7 +21,7 @@ PostgreSQL documentation
 
  <refsynopsisdiv>
 <synopsis>
-DISCARD { ALL | PLANS | TEMPORARY | TEMP }
+DISCARD { ALL | PLANS | SEQUENCES | TEMPORARY | TEMP }
 </synopsis>
  </refsynopsisdiv>
 
@@ -66,6 +66,15 @@ DISCARD { ALL | PLANS | TEMPORARY | TEMP }
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term><literal>SEQUENCES</literal></term>
+    <listitem>
+     <para>
+      Discards all cached sequence values.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><literal>ALL</literal></term>
     <listitem>
@@ -83,6 +92,7 @@ UNLISTEN *;
 SELECT pg_advisory_unlock_all();
 DISCARD PLANS;
 DISCARD TEMP;
+DISCARD SEQUENCES;
 </programlisting></para>
     </listitem>
    </varlistentry>

src/backend/commands/discard.c

@@ -18,13 +18,14 @@
 #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 | TEMP | PLANS }
+ * DISCARD { ALL | SEQUENCES | TEMP | PLANS }
  */
 void
 DiscardCommand(DiscardStmt *stmt, bool isTopLevel)
@@ -39,6 +40,10 @@ DiscardCommand(DiscardStmt *stmt, bool isTopLevel)
 			ResetPlanCache();
 			break;
 
+		case DISCARD_SEQUENCES:
+			ResetSequenceCaches();
+			break;
+
 		case DISCARD_TEMP:
 			ResetTempTableNamespace();
 			break;
@@ -69,4 +74,5 @@ DiscardAll(bool isTopLevel)
 	LockReleaseAll(USER_LOCKMETHOD, true);
 	ResetPlanCache();
 	ResetTempTableNamespace();
+	ResetSequenceCaches();
 }

src/backend/commands/sequence.c

@@ -1602,3 +1602,19 @@ seq_redo(XLogRecPtr lsn, XLogRecord *record)
 
 	pfree(localpage);
 }
+
+/*
+ * Flush cached sequence information.
+ */
+void
+ResetSequenceCaches(void)
+{
+	SeqTableData *next;
+
+	while (seqtab != NULL)
+	{
+		next = seqtab->next;
+		free(seqtab);
+		seqtab = seqtab->next;
+	}
+}

src/backend/parser/gram.y

@@ -1674,7 +1674,7 @@ CheckPointStmt:
 
 /*****************************************************************************
  *
- * DISCARD { ALL | TEMP | PLANS }
+ * DISCARD { ALL | TEMP | PLANS | SEQUENCES }
  *
  *****************************************************************************/
 
@@ -1703,6 +1703,13 @@ DiscardStmt:
 					n->target = DISCARD_PLANS;
 					$$ = (Node *) n;
 				}
+			| DISCARD SEQUENCES
+				{
+					DiscardStmt *n = makeNode(DiscardStmt);
+					n->target = DISCARD_SEQUENCES;
+					$$ = (Node *) n;
+				}
+
 		;
 
 

src/backend/tcop/utility.c

@@ -2190,6 +2190,9 @@ CreateCommandTag(Node *parsetree)
 				case DISCARD_TEMP:
 					tag = "DISCARD TEMP";
 					break;
+				case DISCARD_SEQUENCES:
+					tag = "DISCARD SEQUENCES";
+					break;
 				default:
 					tag = "???";
 			}

src/bin/psql/tab-complete.c

@@ -2378,7 +2378,7 @@ psql_completion(char *text, int start, int end)
 	else if (pg_strcasecmp(prev_wd, "DISCARD") == 0)
 	{
 		static const char *const list_DISCARD[] =
-		{"ALL", "PLANS", "TEMP", NULL};
+		{"ALL", "PLANS", "SEQUENCES", "TEMP", NULL};
 
 		COMPLETE_WITH_LIST(list_DISCARD);
 	}

src/include/commands/sequence.h

@@ -74,6 +74,7 @@ extern Datum pg_sequence_parameters(PG_FUNCTION_ARGS);
 extern Oid	DefineSequence(CreateSeqStmt *stmt);
 extern Oid	AlterSequence(AlterSeqStmt *stmt);
 extern void ResetSequence(Oid seq_relid);
+extern void ResetSequenceCaches(void);
 
 extern void seq_redo(XLogRecPtr lsn, XLogRecord *rptr);
 extern void seq_desc(StringInfo buf, uint8 xl_info, char *rec);

src/include/nodes/parsenodes.h

@@ -2543,6 +2543,7 @@ typedef enum DiscardMode
 {
 	DISCARD_ALL,
 	DISCARD_PLANS,
+	DISCARD_SEQUENCES,
 	DISCARD_TEMP
 } DiscardMode;
 

src/test/regress/expected/sequence.out

@@ -163,6 +163,9 @@ SELECT nextval('sequence_test'::text);
       99
 (1 row)
 
+DISCARD SEQUENCES;
+SELECT currval('sequence_test'::regclass);
+ERROR:  currval of sequence "sequence_test" is not yet defined in this session
 DROP SEQUENCE sequence_test;
 -- renaming sequences
 CREATE SEQUENCE foo_seq;

src/test/regress/sql/sequence.sql

@@ -72,6 +72,8 @@ SELECT setval('sequence_test'::regclass, 32);
 SELECT nextval('sequence_test'::text);
 SELECT setval('sequence_test'::regclass, 99, false);
 SELECT nextval('sequence_test'::text);
+DISCARD SEQUENCES;
+SELECT currval('sequence_test'::regclass);
 
 DROP SEQUENCE sequence_test;