Re: currval() race condition on server?

[Achilleas Mantzios <achill(at)matrix(dot)gatewaynet(dot)com>]

Στις Δευτέρα 23 Οκτώβριος 2006 16:49, ο/η Adriaan Joubert έγραψε:
> 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.

What do you mean here? Inserts it into the row inserted....

>
> 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

That normally means that no nextval has been called on the sequence during the 
session in question.
Can you give us the trigger code?

>
> 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.
>

In any case double check that the server version/JDBC version match.

> 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?
>
> Cheers,
>
> Adriaan
>
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-- 
Achilleas Mantzios