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.

10 files changed, 53 insertions, 4 deletions

diff --git a/doc/src/sgml/ref/discard.sgml b/doc/src/sgml/ref/discard.sgml
index 65ebbae1385..762f8657116 100644
--- a/doc/src/sgml/ref/discard.sgml
+++ b/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>
 
@@ -67,6 +67,15 @@ DISCARD { ALL | PLANS | TEMPORARY | TEMP }
    </varlistentry>
 
    <varlistentry>
+    <term><literal>SEQUENCES</literal></term>
+    <listitem>
+     <para>
+      Discards all cached sequence values.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
     <term><literal>ALL</literal></term>
     <listitem>
      <para>
@@ -83,6 +92,7 @@ UNLISTEN *;
 SELECT pg_advisory_unlock_all();
 DISCARD PLANS;
 DISCARD TEMP;
+DISCARD SEQUENCES;
 </programlisting></para>
     </listitem>
    </varlistentry>
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;