Re: serial type; race conditions

> How does currval work if you are not inside a transaction. I have
> been experimenting with inserting into a table that has a sequence.
> If the insert fails (not using a transaction) because of bad client input
> then the next insert gets the proper next number in the sequence.

If you are in a transaction, and the INSERT succeeds but the transaction
rolls back, the sequence does not get reused. Each backend has a local
variable that holds the most recent sequence assigned. That is how
currval works.

>
> given sequence 1,2,3,4,5 exists
> insert into table date 1/111/01 (obviously wrong) insert fails...
> try again with good data, insert succeeds and gets number 6 in the
> sequence.
>
> i'm getting what I want. A sequence number that does not increment
> on a failed insert. However, how do I get the assigned sequence
> number with currval when I am not using a transaction? What
> happens when multiple users are inserting at the same time?
>
> I am trying to create a sequence with out any "missing" numbers. If
> there is a failure to insert, and a sequence number is "taken". I want
> the empty row.
>
> Thanks, .... it is getting clearer....

You really can't use sequences with no gaps. Sequence numbers are not
_held_ until commit because it would block other backends trying to get
sequence numbers.

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Bruce Momjian | http://candle.pha.pa.us
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