Fix for bug 3202643: Sequence error

For the following sequence:
create SEQUENCE seq;
select nextval('seq');
select currval('seq');
select nextval('seq');

XC was returning 1 -> 100 -> 100 -> 101
PostgreSQL was returning 1 -> 100 -> 1 -> 100

This is corrected.
We also check if nextval has been called once in a session
when using currval.

This is to correspond with PostgreSQL.

2 files changed, 29 insertions, 35 deletions

diff --git a/src/backend/commands/sequence.c b/src/backend/commands/sequence.c
index a0be960859..5105200417 100644
--- a/src/backend/commands/sequence.c
+++ b/src/backend/commands/sequence.c
@@ -619,7 +619,13 @@ nextval_internal(Oid relid)
 		/* Update the on-disk data */
 		seq->last_value = result; /* last fetched number */
 		seq->is_called = true;
-	} else
+
+		/* save info in local cache */
+		elm->last = result;			/* last returned number */
+		elm->cached = result;		/* last fetched number */
+		elm->last_valid = true;
+	}
+	else
 	{
 #endif
 	last = next = result = seq->last_value;
@@ -798,21 +804,6 @@ currval_oid(PG_FUNCTION_ARGS)
 	/* open and AccessShareLock sequence */
 	init_sequence(relid, &elm, &seqrel);
 
-#ifdef PGXC
-	if (IS_PGXC_COORDINATOR)
-	{
-		char *seqname = GetGlobalSeqName(seqrel, NULL, NULL);
-
-		result = (int64) GetCurrentValGTM(seqname);
-		if (result < 0)
-			ereport(ERROR,
-					(errcode(ERRCODE_CONNECTION_FAILURE),
-					 errmsg("GTM error, could not obtain sequence value")));
-		pfree(seqname);
-	}
-	else
-	{
-#endif
 
 	if (pg_class_aclcheck(elm->relid, GetUserId(), ACL_SELECT) != ACLCHECK_OK &&
 		pg_class_aclcheck(elm->relid, GetUserId(), ACL_USAGE) != ACLCHECK_OK)
@@ -827,12 +818,21 @@ currval_oid(PG_FUNCTION_ARGS)
 				 errmsg("currval of sequence \"%s\" is not yet defined in this session",
 						RelationGetRelationName(seqrel))));
 
-	result = elm->last;
-
 #ifdef PGXC
+	if (IS_PGXC_COORDINATOR)
+	{
+		char *seqname = GetGlobalSeqName(seqrel, NULL, NULL);
+
+		result = (int64) GetCurrentValGTM(seqname);
+		if (result < 0)
+			ereport(ERROR,
+					(errcode(ERRCODE_CONNECTION_FAILURE),
+					 errmsg("GTM error, could not obtain sequence value")));
+		pfree(seqname);
 	}
+#else
+	result = elm->last;
 #endif
-
 	relation_close(seqrel, NoLock);
 
 	PG_RETURN_INT64(result);
diff --git a/src/gtm/main/gtm_seq.c b/src/gtm/main/gtm_seq.c
index 570636be58..caccd35a2b 100644
--- a/src/gtm/main/gtm_seq.c
+++ b/src/gtm/main/gtm_seq.c
@@ -660,16 +660,8 @@ GTM_SeqGetCurrent(GTM_SequenceKey seqkey)
 
 	GTM_RWLockAcquire(&seqinfo->gs_lock, GTM_LOCKMODE_WRITE);
 
-	/*
-	 * If this is the first call to the sequence, set the value to the start
-	 * value and mark the sequence as 'called'
-	 */
-	if (!SEQ_IS_CALLED(seqinfo))
-	{
-		seqinfo->gs_value = seqinfo->gs_init_value;
-		seqinfo->gs_called = true;
-	}
-	value = seqinfo->gs_value;
+	value = seqinfo->gs_last_value;
+
 	GTM_RWLockRelease(&seqinfo->gs_lock);
 	seq_release_seqinfo(seqinfo);
 	return value;
@@ -693,6 +685,8 @@ GTM_SeqSetVal(GTM_SequenceKey seqkey, GTM_Sequence nextval, bool iscalled)
 
 	GTM_RWLockAcquire(&seqinfo->gs_lock, GTM_LOCKMODE_WRITE);
 
+	seqinfo->gs_last_value = seqinfo->gs_value;
+
 	if (seqinfo->gs_value != nextval)
 		seqinfo->gs_value = nextval;
 
@@ -734,7 +728,7 @@ GTM_SeqGetNext(GTM_SequenceKey seqkey)
 	 */
 	if (!SEQ_IS_CALLED(seqinfo))
 	{
-		value = seqinfo->gs_value = seqinfo->gs_init_value;
+		value = seqinfo->gs_last_value = seqinfo->gs_value = seqinfo->gs_init_value;
 		seqinfo->gs_called = true;
 		GTM_RWLockRelease(&seqinfo->gs_lock);
 		seq_release_seqinfo(seqinfo);
@@ -749,9 +743,9 @@ GTM_SeqGetNext(GTM_SequenceKey seqkey)
 		 * InvalidSequenceValue
 		 */
 		if (seqinfo->gs_max_value - seqinfo->gs_increment_by >= seqinfo->gs_value)
-			value = seqinfo->gs_value = seqinfo->gs_value + seqinfo->gs_increment_by;
+			value = seqinfo->gs_last_value = seqinfo->gs_value = seqinfo->gs_value + seqinfo->gs_increment_by;
 		else if (SEQ_IS_CYCLE(seqinfo))
-			value = seqinfo->gs_value = seqinfo->gs_min_value;
+			value = seqinfo->gs_last_value = seqinfo->gs_value = seqinfo->gs_min_value;
 		else
 		{
 			GTM_RWLockRelease(&seqinfo->gs_lock);
@@ -774,9 +768,9 @@ GTM_SeqGetNext(GTM_SequenceKey seqkey)
 		 * descending sequences. So we don't need special handling below
 		 */
 		if (seqinfo->gs_min_value - seqinfo->gs_increment_by <= seqinfo->gs_value)
-			value = seqinfo->gs_value = seqinfo->gs_value + seqinfo->gs_increment_by;
+			value = seqinfo->gs_value = seqinfo->gs_last_value = seqinfo->gs_value + seqinfo->gs_increment_by;
 		else if (SEQ_IS_CYCLE(seqinfo))
-			value = seqinfo->gs_value = seqinfo->gs_max_value;
+			value = seqinfo->gs_value = seqinfo->gs_last_value = seqinfo->gs_max_value;
 		else
 		{
 			GTM_RWLockRelease(&seqinfo->gs_lock);
@@ -810,7 +804,7 @@ GTM_SeqReset(GTM_SequenceKey seqkey)
 	}
 
 	GTM_RWLockAcquire(&seqinfo->gs_lock, GTM_LOCKMODE_WRITE);
-	seqinfo->gs_value = seqinfo->gs_init_value;
+	seqinfo->gs_value = seqinfo->gs_last_value = seqinfo->gs_init_value;
 	GTM_RWLockRelease(&seqinfo->gs_lock);
 
 	seq_release_seqinfo(seqinfo);