Re: Libpq support to connect to standby server as priority

On Thu, Feb 14, 2019 at 1:04 PM Tsunakawa, Takayuki <
tsunakawa(dot)takay(at)jp(dot)fujitsu(dot)com> wrote:

> From: Haribabu Kommi [mailto:kommi(dot)haribabu(at)gmail(dot)com]
> > No. It's not good if the user has to be bothered by
> > default_transaction_read_only when he simply wants to a standby.
> >
> >
> >
> > OK. Understood.
> > so if we are going to differentiate between readonly and standby types,
> > then I still
> > feel that adding a prefer-read to target_session_attrs is still valid
> > improvement.
>
> I agree that it's valid improvement to add prefer-read to
> target_session_attr, as a means to "get a read-only session."
>
> > But the above improvement can be enhanced once the base work of
> GUC_REPORT
> > is finished.
>
> Is it already in progress in some thread, or are you trying to start from
> scratch? (I may have done it, but I don't remember it well...)
>
> > Yes, I want to work on this patch, hopefully by next commitfest. In case
> > if I didn't get time,
> > I can ask for your help.
>
> I'm glad to hear that. Sure. I'd like to review your patch, and possibly
> add/modify code if necessary. Are you going to add
> target_server_type={primary | standby | prefer_standby} as well as add
> prefer-read to target_session_attr?
>
>
> > (I wonder which of server_type or server_role feels natural in
> > English.)
> >
> >
> >
> > server_type may be good as it stands with connection option
> > (target_server_type).
>
> Thanks, agreed. That also follows PgJDBC's targetServerType.
>

Here I attached first set of patches that implemented the prefer-read
option after reporting
the transaction_read_only GUC to client. Along the lines of adding
prefer-read option patch,

1. I refactor the existing code to reduce the duplicate.
2. Added a enum to represent the user requested target_session_attrs type,
this is used in
comparison instead of doing a strcmp always.
3. Existing read-write code is modified to use the new reported GUC instead
of executing the
show command.

Basic patches are working, there may still need some documentation works.

Now I will add the another parameter target_server_type to choose the
primary, standby or prefer-standby
as discussed in the upthreads with a new GUC variable.

Regards,
Haribabu Kommi
Fujitsu Australia