Paul Millar <paul.millar@desy.de> writes:
> Hi all,
>
> I've a question regarding unique constraints, which I've tried to describe in
> general terms, to keep things simple.
>
> I've working on an application that, amongst other things, may add a row to a
> table. This table has a primary key defined over two (of the three) fields,
> which forces the combined value to be unique.
>
> An end-user of this system can cause the application to add a row to a table,
> based on data supplied by that end-user (a create-like command). It can
> happen that end-users repeat themselves: rerunning the same activity with the
> same data. Logically, repeating the activity doesn't make sense; the
> application should fail the second (and all subsequent) attempts with a
> meaningful error message.
>
> When writing the application, there was a deliberate design decision: rather
> than a read-modify-write cycle, with the corresponding overhead of locking and
> the resulting serialisation, the software simply lets the INSERT fail (due to
> the primary-key uniqueness constraint). If this happens, the transaction is
> rolled back and an error message returned.
>
> The software can identify whether the problem is due to an end-user repeating
> an earlier action by looking at the class code from the SQL error ("23" ==
> Constraint Violation). This allows us to return the correct error.
>
> This works fine: the correct error message is reported and the system behaves
> as it should. There's one problem: if a user repeats their activity then
> PostgreSQL logs the corresponding constraint violation:
>
> ERROR: duplicate key value violates unique constraint [..]
>
> The log files may contain many such messages, depending on the usage-pattern
> of the end-user. Including all these messages in the log file is distracting.
>
> The question is: can we suppress the logging of these message .. but allow
> other error messages to be logged normally?
Sure. Modify the application as such...
begin;
do whatever;
set log_min_messages to fatal;
insert...; -could fail
reset log_min_messages;
commit;
> Cheers,
>
> Paul.
--
Jerry Sievers
Postgres DBA/Development Consulting
e: gsievers19@comcast.net
p: 305.321.1144
