Re: Regarding ALTER Command

Hello,

We are planning to use latest postgres version. I have one query as below:

One more thing I have to mention is that we are using 2 postmasters running
on different machines and both are accessing same data directory. (i.e both
the machines uses same tables or the databases)

In that case if from first machine, continuous INSERT operation on any table
are going on and from the second we have to update the same table using
ALTER command.

Would this create any problem because INSERT and ALTER operations are
executed from the two different postmasters but for a same data directory?

Would there be any data loss or in this case also ALTER will block all the
new accesses to the table?

Thanks,
Soni

On 6/7/06, Jim C. Nasby <jnasby(at)pervasive(dot)com> wrote:
>
> On Wed, Jun 07, 2006 at 06:13:11PM +0530, soni de wrote:
> > Hello,
> >
> >
> >
> > We have database on which continueous operations of INSERT, DELETE,
> UPDATE
> > are going on, In the mean time irrespective of INSERT and UPDATE we want
> to
> > ALTER some filelds from the table can we do that?
> >
> > Would the ALTER command on heavily loaded database create any perfomance
> > problem?
> >
> > Is it feasible to do ALTER when lots of INSERT operations are going on?
>
> The problem you'll run into is that ALTER will grab an exclusive table
> lock. If *all* the transactions hitting the table are very short, this
> shouldn't be too big of an issue; the ALTER will block all new accesses
> to the table while it waits for all the pending ones to complete, but if
> all the pending ones complete quickly it shouldn't be a big issue.
>
> If one of the pending statements takes a long time though...
>
> > Postgresql version we are using is -- PostgreSQL 7.2.4
>
> You very badly need to upgrade. 7.2 is no longer supported, and there
> have been over a half-dozen data loss bugs fixed since then.
> --
> Jim C. Nasby, Sr. Engineering Consultant jnasby(at)pervasive(dot)com
> Pervasive Software http://pervasive.com work: 512-231-6117
> vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461
>