Horton

Re: Libpq support to connect to standby server as priority

Haribabu Kommi <kommi.haribabu@gmail.com>

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From: Haribabu Kommi <kommi.haribabu@gmail.com>
To: "Tsunakawa, Takayuki" <tsunakawa.takay@jp.fujitsu.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Laurenz Albe <laurenz.albe@cybertec.at>, Tom Lane <tgl@sss.pgh.pa.us>, Dave Cramer <pg@fastcrypt.com>, Jing Wang <jingwangian@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2019-03-21T06:25:49Z
Lists: pgsql-hackers 
On Wed, Mar 20, 2019 at 5:01 PM Tsunakawa, Takayuki <
tsunakawa.takay@jp.fujitsu.com> wrote:

> From: Robert Haas [mailto:robertmhaas@gmail.com]
> > I really dislike having both target_sesion_attrs and
> > target_server_type.  It doesn't solve any actual problem.  master,
> > slave, prefer-save, or whatever you like could be put in
> > target_session_attrs just as easily, and then we wouldn't end up with
> > two keywords doing closely related things.  'master' is no more or
> > less a server attribute than 'read-write'.
>
> Hmm, that may be OK.  At first, I felt it strange to treat the server type
> (primary or standby) as a session attribute.  But we can see the server
> type as one attribute in a sense that a session is established for.  I'm
> inclined to agree with:
>
> target_session_attr = {any | read-write | read-only | prefer-read |
> primary | standby | prefer-standby}
>

Thanks for your suggestions.

Based on the above new options that can be added to target_session_attrs,

primary - it is just an alias to the read-write option.
standby, prefer-standby - These options should check whether server is
running in recovery mode or not
instead of checking whether server accepts read-only connections or not?

Regards,
Haribabu Kommi
Fujitsu Australia

Commits

  1. Make test_target_session_attrs more robust against connection failure.

  2. Extend the abilities of libpq's target_session_attrs parameter.

  3. Mark default_transaction_read_only as GUC_REPORT.

  4. Introduce a new GUC_REPORT setting "in_hot_standby".

  5. Avoid spamming the client with multiple ParameterStatus messages.

  6. Avoid harmless Valgrind no-buffer-pin errors.

  7. Restructure libpq code to remove some duplicity

  8. libpq: Add target_session_attrs parameter.