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.

9 files changed, 42 insertions, 3 deletions

diff --git a/src/backend/commands/discard.c b/src/backend/commands/discard.c
index 76f3ab672ad..9010368f577 100644
--- a/src/backend/commands/discard.c
+++ b/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();
 }
diff --git a/src/backend/commands/sequence.c b/src/backend/commands/sequence.c
index ddfaf3bd293..3ec6b7654aa 100644
--- a/src/backend/commands/sequence.c
+++ b/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;
+	}
+}
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index a9812af7cfc..0efe1705e24 100644
--- a/src/backend/parser/gram.y
+++ b/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;
+				}
+
 		;
 
 
diff --git a/src/backend/tcop/utility.c b/src/backend/tcop/utility.c
index b1023c4e882..fffaa35d344 100644
--- a/src/backend/tcop/utility.c
+++ b/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 = "???";
 			}
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index b3de387b941..255061c1c41 100644
--- a/src/bin/psql/tab-complete.c
+++ b/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);
 	}
diff --git a/src/include/commands/sequence.h b/src/include/commands/sequence.h
index 6bd4892cfc1..ffafe6c52f4 100644
--- a/src/include/commands/sequence.h
+++ b/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);
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index 51fef68ca3c..e5235cbf40f 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -2543,6 +2543,7 @@ typedef enum DiscardMode
 {
 	DISCARD_ALL,
 	DISCARD_PLANS,
+	DISCARD_SEQUENCES,
 	DISCARD_TEMP
 } DiscardMode;
 
diff --git a/src/test/regress/expected/sequence.out b/src/test/regress/expected/sequence.out
index 87feb08b14a..37e9a8cfa1a 100644
--- a/src/test/regress/expected/sequence.out
+++ b/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;
diff --git a/src/test/regress/sql/sequence.sql b/src/test/regress/sql/sequence.sql
index a32e0494a02..31cbc926c02 100644
--- a/src/test/regress/sql/sequence.sql
+++ b/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;