Re: Running two queries concurrently?

Start your journey here:

http://www.postgresql.org/docs/9.3/interactive/mvcc.html


James David Smith wrote
> So my question really is, is this possible? I would have thought that
> perhaps QueryOne puts a lock on TABLE A and TABLE B while it is
> selecting data from one and inserting into the other, but maybe not?

Yes.  Locks do occur BUT

1) these are not "exclusive" locks; multiple clients can interact according
to rules defined in the documentation

2) locks can be done on a row (or at worse group of rows) basis; not just
table


> At the moment I have to do QueryOne and then QueryTwo quite a few
> times, but have been doing them one after another. Maybe I can
> actually run them at the same time?

You do have the ability to run these simultaneously in separate sessions;
whether you get any performance/time gain from doing so depends on a number
of factors such as disk i/o and just randomness as to where data is located
- not to mention your processor setup.

I am hoping you are using something like:

INSERT INTO tableB
SELECT ... FROM tableA WHERE ...

20 minutes for 10,000 records seems extremely long...it sounds like you
might also want to learn about:

http://www.postgresql.org/docs/9.3/interactive/indexes.html

and also:

http://www.postgresql.org/docs/9.3/interactive/using-explain.html

the later to help you (and others) pin-point where in the query (assuming
you aren't pulling 10k records over the network to your client then sending
them back during the insert) you are eating all that time.

David J.



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