+ Datum
+ lastval(PG_FUNCTION_ARGS)
+ {
+ Relation seqrel;
+ int64 result;
+ + if (last_used_seq == NULL) {
+ ereport(ERROR,
+ (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+ errmsg("nextval have not been used in the current session")));
+ }
"has not been" would be more better English.
+ + seqrel = relation_open(last_used_seq->relid, NoLock);
+ + acquire_share_lock (seqrel, last_used_seq);
+ + if (pg_class_aclcheck(last_used_seq->relid, GetUserId(), ACL_SELECT) != ACLCHECK_OK)
+ ereport(ERROR,
+ (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+ errmsg("permission denied for sequence with OID %d",
+ last_used_seq->relid)));
"%d" is always the wrong formatting sequence for OIDs (they are unsigned, hence %u). But in any case user-visible error messages should specify the name of the sequence, which you can get via RelationGetRelationName(seqrel)
+ + if (last_used_seq->increment == 0) /* nextval/read_info were not called */
+ ereport(ERROR,
+ (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+ errmsg("currval of sequence with OID %d is not yet defined in this session",
+ last_used_seq->relid)));
See above; however, when will this error actually be invoked? (The comment is wrong, as last_used_seq won't be defined if nextval has not been called.)
/* + * If we haven't touched the sequence already in this transaction, + * we need to acquire AccessShareLock. We arrange for the lock to + * be owned by the top transaction, so that we don't need to do it + * more than once per xact. + */ + static void + acquire_share_lock (Relation seqrel, + SeqTableData *data)
Confusing SeqTable and SeqTableData * is bad style. I personally don't like putting pointers into typedefs, but since the PG code does this, SeqTable should be used consistently rather than SeqTableData *. The same applies to the definition of "last_used_seq".
Comments on behavior:
neilc=# select setval('foo', 500);
setval
--------
500
(1 row)neilc=# select lastval();
lastval
---------
500
(1 row)I'm not sure it's necessarily _wrong_ to update lastval() on both setval and nextval, but if that's the behavior we're going to implement, it should surely be documented.
neilc=# create sequence bar ; select nextval ('bar') ; drop sequence bar;
CREATE SEQUENCE
nextval
---------
1
(1 row)DROP SEQUENCE neilc=# select lastval(); ERROR: XX000: could not open relation with OID 16389
Needs a friendlier error message.
-Neil
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