Horton

RE: Libpq support to connect to standby server as priority

Tsunakawa, Takayuki <tsunakawa.takay@jp.fujitsu.com>

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From: "Tsunakawa, Takayuki" <tsunakawa.takay@jp.fujitsu.com>
To: 'Haribabu Kommi' <kommi.haribabu@gmail.com>
Cc: Laurenz Albe <laurenz.albe@cybertec.at>, Tom Lane <tgl@sss.pgh.pa.us>, Dave Cramer <pg@fastcrypt.com>, Robert Haas <robertmhaas@gmail.com>, "Jing Wang" <jingwangian@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2019-02-14T02:03:32Z
Lists: pgsql-hackers 
From: Haribabu Kommi [mailto:kommi.haribabu@gmail.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.


Regards
Takayuki Tsunakawa

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.