Re: good exception handling archiecutre

On 16 Aug 2010, at 10:45, <Atul(dot)Goel(at)globaldatapoint(dot)com> <Atul(dot)Goel(at)globaldatapoint(dot)com> wrote:

> Hi Alban,
>
> Thanks for the reply.
>
> I checked that Notify will not work till the transaction is commited. So in our case since the transaction is being rolled back there will be no notify.

Ah, you're right! I totally forgot about that...

> Is there any other way of inter process communication in Postgres.

Of course there is :)

There's nothing stopping you from writing a few custom functions in an untrusted language that does your IPC for you. C comes to mind, but PL/Perlu, PL/PythonU, etc. should be able to do it as well (and probably easier).

Usually if you're talking about performing I/O external to the database you'll get warned that transactions involving those calls can't be rolled back, but in this case that's exactly what you want.

Now I know that Postgres uses some IPC internally as well (at least shared memory), so maybe it's possible to use some of the internal mechanisms. I have no idea whether that's possible or at all advisable, I'm sure someone (probably Tom) will chime in regarding that.

Cheers!

> -----Original Message-----
> From: Alban Hertroys [mailto:dalroi(at)solfertje(dot)student(dot)utwente(dot)nl]
> Sent: 13 August 2010 17:50
> To: Atul Goel
> Cc: pgsql-general(at)postgresql(dot)org
> Subject: Re: [GENERAL] good exception handling archiecutre
>
> On 13 Aug 2010, at 14:07, <Atul(dot)Goel(at)globaldatapoint(dot)com> <Atul(dot)Goel(at)globaldatapoint(dot)com> wrote:
>
>> How can we do error logging in Postgres. I am trying to create a LOG_AND_STOP method which would be generic to the code. I have pasted the code I have written. This code returns no data which is understandable as the error is thrown to the external world.
>>
>> Can I write the code somehow.
>>
>> CREATE SCHEMA test
>> AUTHORIZATION postgres;
>>
>> CREATE TABLE test.error_log
>> (
>> error_desc text
>> );
>>
>>
>> CREATE OR REPLACE FUNCTION test.log_and_stop(err_desc text)
>> RETURNS void AS
>> $BODY$
>> Declare
>> x integer;
>> begin
>> begin
>> insert into test.error_log values (err_desc);
>> end;
>> begin
>> raise exception '%',err_desc;
>
> Your transaction got rolled back here, hence the lack of data in your error_log table.
>
> I don't think there's any way to log errors into a table from within the same transaction, you'll probably need to use a separate connection for the logging. I think LISTEN/NOTIFY may come in handy there.
>
>> end;
>> end;
>> $BODY$
>> LANGUAGE 'plpgsql' VOLATILE
>> COST 100;
>> ALTER FUNCTION test.log_and_stop(text) OWNER TO postgres;
>
> Alban Hertroys
>
> --
> If you can't see the forest for the trees,
> cut the trees and you'll see there is no forest.
>
>
>
>
>
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Alban Hertroys

--
If you can't see the forest for the trees,
cut the trees and you'll see there is no forest.

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