Re: currval() race condition on server?

On 23-Oct-06, at 9:49 AM, Adriaan Joubert wrote:

> Hi,
>
>     I've run into an intermittent problem with our code recently. We
> have the following set-up:
>
> table A : some data table
> table B : a history table for table A
>
> A trigger copies the old version of a row into table B whenever an
> update is done on table A. Both A and B contain an audit number,
> and the trigger obtains an audit number from a sequence and inserts
> it into the row inserted into table A.
>
> For some bookkeeping purposes I need the new audit number back from
> the update, so I submit a prepared statement through jdbc of the form
>
> UPDATE A SET ....; SELECT currval('ip_audit_seq');
>
> On the first call I get
>
>  ERROR: currval of sequence "ip_audit_seq" is not yet defined in
> this session
currval is only defined after you call nextval in that connection.
>
> Note that this works without any trouble if I issue the commands in
> a transaction through psql, and this used to work in earlier
> versions of postgres.
>
> We have a lot of users on very high latency links, so it is
> important for the responsiveness of the application to try to do
> the update and select in a single database trip.
>
> So I'm wondering whether there is some type of race condition,
> where the selection of the new value from ip_audit_seq is not
> available to the currval function straight away? Anybody got any
> ideas on this?

There is no race condition
>
> Cheers,
>
> Adriaan
>
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