Re: Libpq support to connect to standby server as priority

On Tue, Jul 17, 2018 at 12:42 AM Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at>
wrote:

> Haribabu Kommi wrote:
> > > On Wed, Jul 4, 2018 at 11:14 PM Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at>
> wrote:
> > > > Haribabu Kommi wrote:
> > > >
> > > > - I think the construction with "read_write_host_index" makes the
> code even more
> > > > complicated than it already is.
> > > >
> > > > What about keeping the first successful connection open and
> storing it in a
> > > > variable if we are in "prefer-read" mode.
> > > > If we get the read-only connection we desire, close that cached
> connection,
> > > > otherwise use it.
> > >
> > > Even if we add a variable to cache the connection, I don't think the
> logic of checking
> > > the next host for the read-only host logic may not change, but the
> extra connection
> > > request to the read-write host again will be removed.
> >
> > I evaluated your suggestion of caching the connection and reuse it when
> there is no
> > read only server doesn't find, but I am thinking that it will add more
> complexity and also
> > the connection to the other servers delays, the cached connection may be
> closed by
> > the server also because of timeout.
> >
> > I feel the extra time during connection may be fine, if user is
> preferring the prefer-read
> > mode, instead of adding more complexity in handling the cached
> connection?
> >
> > comments?
>
> I tested the new patch, and it works as expected.
>

Thanks for the confirmation.

> I don't think that time-out of the cached session is a valid concern,
> because that
> would have to be a really short timeout.
> On the other hand, establishing the connection twice (first to check if it
> is read-only,
> then again because no read-only connection is found) can be quite costly.
>
> But that is a matter of debate, as is the readability of the code.
>

Thanks for your opinion, let's wait for opinion from others also.
I can go for the modification, if others also find it useful.

Regards,
Haribabu Kommi
Fujitsu Australia