From: | Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at> |
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To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Jing Wang <jingwangian(at)gmail(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>, "Tsunakawa, Takayuki" <tsunakawa(dot)takay(at)jp(dot)fujitsu(dot)com> |
Subject: | Re: Libpq support to connect to standby server as priority |
Date: | 2018-11-16 17:56:11 |
Message-ID: | 84d7a264fb5ad46873f6e40e10c3ee92983c55ca.camel@cybertec.at |
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Lists: | pgsql-hackers |
Tom Lane wrote:
> > As it is now, the patch doesn't keep two connections open. It remembers
> > the index of the host of the first successful writable connection, but
> > closes the connection, and opens another one to that host if no read-only
> > host can be found.
>
> Oh! The reason I assumed it wasn't doing that is that such a behavior
> seems completely insane. If the point is to keep down the load on your
> master server, then connecting only to immediately disconnect is not
> a friendly way to do that --- even without counting the fact that you
> might later come back and connect again.
That's why I had argued initially to keep the session open, but you
seem to dislike that idea as well.
> If that's the best we can do, we should forget the whole feature and
> just recommend putting slave servers first in your hosts list when
> you want prefer-slave.
If you know which is which, certainly.
But in a setup with automated failover you cannot be certain which is which.
That's what the proposed feature targets.
Yours,
Laurenz Albe
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