Re: Concurrent Inserts

Hi,

Actually i am using a FDW , in which the data is written into a single
file. So when i do concurrent inserts , the data is written into the file
simultaneously and this is causing a data corruption . Is TABLE LOCK the
only option available ??

--Harsha

On Wed, Jan 21, 2015 at 3:22 PM, Albe Laurenz <laurenz(dot)albe(at)wien(dot)gv(dot)at>
wrote:

> sri harsha wrote:
> > Is there any way to stop concurrent inserts to happen on a single
> table ??
> >
> > Query 1 : INSERT INTO TABLE_A SELECT * FROM TABLE1;
> > Query 2 : INSERT INTO TABLE_A SELECT * FROM TABLE2;
> > Query 3 : SELECT * FROM TABLE_A;
> >
> > Assume i have the above queries. Query 1 and Query 3 can occur
> concurrently . If one insert is taking
> > place , the other should wait. How do i achieve this ??
>
> Is that a typo and you really mean "query 1 an query 2" above?
>
> Why would you want to prevent concurrent inserts?
> Maybe you don't really need to hobble your performance like that.
>
> If you really want that, it is easy with table locks.
> Your INSERT could look like that:
>
> BEGIN;
> LOCK table_a IN EXCLUSIVE MODE;
> INSERT INTO table_a ...
> COMMIT;
>
> > How do the concurrent inserts take place in postgres ?? Is data
> stored temporarily for both queries
> > separately and then written into the table ??
>
> No, it is written to the table concurrently.
> A table is organized in pages of 8KB each, and there is no problem with
> writing to
> different pages concurrently.
>
> Yours,
> Laurenz Albe
>