Re: Libpq support to connect to standby server as priority

On 2019-Oct-01, Greg Nancarrow wrote:

> On Wed, Sep 11, 2019 at 10:17 AM Alvaro Herrera from 2ndQuadrant
> <alvherre@alvh.no-ip.org> wrote:
> >
> > Oh, oops. Here they are then.
>
> With the permission of the original patch author, Haribabu Kommi, I’ve
> rationalized the existing 8 patches into 3 patches, merging patches
> 1-5 and 6-7, and tidying up some documentation and code comments. I
> also rebased them to the latest PG12 source code (as of October 1,
> 2019). The patch code itself is the same, except for some version
> checks that I have updated to target the features for PG13 instead of
> PG12.

I've spent some time the last few days going over these patches and the
prior discussion.

I'm not sure I understand why we end up with "prefer-read" in addition
to "prefer-standby" (and similar seeming redundancy between "primary"
and "read-write").  Do we really need more than one way to identify
hosts' roles?  It seems 0001 adds the "prefer-read" modes by checking
transaction_read_only, and later 0002 adds the "prefer-standby" modes by
checking in_recovery.  I'm not sure that we're serving our users very
well by giving them choice that ends up being confusing.  In other words
I think we should do only one of these things, not both.  Maybe merge
0001 and 0002 in a single patch, and get rid of redundant modes.

There were other comments that I think went largely unaddressed, such as
the point that the JDBC driver seems to offer a different syntax for the
configuration, and should we offer a compatibility shim of some sort.
(Frankly, I don't think we need to stress over this too much, but it
seems that it wasn't even discussed.)