Re: Unexpected query result

Hi,

On Mon, Oct 5, 2015 at 5:02 AM, Begin Daniel <jfd553(at)hotmail(dot)com> wrote:

> In order to process a large amount of data I need to run a procedure using
> parallel batch processes.
> The query I run in each process is expected to ...
>
>
It seems, you are trying to achieve the same, what we did. Find my blog
entry
<http://manojadinesh.blogspot.com/2015/07/parallel-operations-with-plpgsql_9.html>,
which may help you in this scenarios.

1- select a bunch of id (500) in a table (wait4processing
>
) containing the list of all records to process
> 2- remove selected records from wait4processing table in order to
> eliminate duplicate processing
> 3- run the procedure (build_contributions_clusters) over the range of
> selected ids
>
> --The query I use:
> With ids as( delete from wait4processing where id in( select id from
> wait4processing limit 500) returning id)
> select build_contributions_clusters(min(id),max(id)) from ids;
>
> The query runs properly if I send it sequentially (wait for the completion
> of the query before sening it again) but it does'nt work when sending
> multiple occurrences in parallel. Seems from the results I got that the
> first query received by the server runs properly but the following ones try
> to process the same first 500 records even if deleted - the
> build_contributions_clusters procedure receive NULL values instead of the
> following 500 records.
>
> Since I am almost certain it is the expected behavior, I would like to like
> to understand why, and I would also appreciate to see alternative queries
> to do the job.
>
> Thanks :-)
>

--

Regards,
Dinesh
manojadinesh.blogspot.com