Re: break table into portions for writing to separate files

Hi,

Does the below kind of approach work for you. I haven't tested this, but
would like to give an idea something like below.

Create a plpgsql function which takes 3 parameters as "From Date", "To
Date" and "Interval".

prev_interval := '0'::interval;

LOOP

IF ( "From Date" + "Interval" <= "To Date") THEN

EXECUTE FORMAT (
$$
COPY (SELECT <Columns Llist> FROM <tableName> WHERE timestamp_column >=%s
AND timestamp_column<%s) TO '%s.csv'
$$,
("From Date" + "prev_interval")::TEXT,
("From Date" + "Interval") ::TEXT,
( Filename || (Extract(Epoch from interval)/60)::BIGINT)::TEXT);

prev_interval := "Interval";

"Interval" := "Interval" + "Interval";

ELSE
EXIT FROM LOOP;
END IF;

END LOOP;

Thanks,
Dinesh
manojadinesh.blogspot.com

On Thu, May 1, 2014 at 11:20 PM, Seb <spluque(at)gmail(dot)com> wrote:

> Hello,
>
> I've been looking for a way to write a table into multiple files, and am
> wondering if there are some clever suggestions. Say we have a table
> that is too large (several Gb) to write to a file that can be used for
> further analyses in other languages. The table consists of a timestamp
> field and several numeric fields, with records every 10th of a second.
> It could be meaningfully broken down into subsets of say 20 minutes
> worth of records. One option is to write a shell script that loops
> through the timestamp, selects the corresponding subset of the table,
> and writes it as a unique file. However, this would be extremely slow
> because each select takes several hours, and there can be hundreds of
> subsets. Is there a better way?
>
> Cheers,
>
> --
> Seb
>
>
>
> --
> Sent via pgsql-general mailing list (pgsql-general(at)postgresql(dot)org)
> To make changes to your subscription:
> http://www.postgresql.org/mailpref/pgsql-general
>