Horton

Re: Libpq support to connect to standby server as priority

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Michael Paquier <michael@paquier.xyz>
Cc: "Tsunakawa, Takayuki" <tsunakawa.takay@jp.fujitsu.com>, Dave Cramer <pg@fastcrypt.com>, Robert Haas <robertmhaas@gmail.com>, "laurenz.albe@cybertec.at" <laurenz.albe@cybertec.at>, Haribabu Kommi <kommi.haribabu@gmail.com>, Jing Wang <jingwangian@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2019-01-15T02:53:17Z
Lists: pgsql-hackers 
Michael Paquier <michael@paquier.xyz> writes:
> On Tue, Jan 15, 2019 at 02:00:57AM +0000, Tsunakawa, Takayuki wrote:
>> The original desire should have been the ability to connect to a
>> primary or a standby.  So, I think we should go back to the original
>> thinking (and not complicate the feature), and create a read only
>> GUC_REPORT variable, say, server_role, that identifies whether the
>> server is a primary or a standby. 

> From the point of view of making sure that a client is really
> connected to  a primary or a standby, this is the best idea around.

There are a couple of issues here:

1. Are you sure there are no use-cases for testing transaction_read_only
as such?

2. What will the fallback implementation be, when connecting to a server
too old to have the variable you want?

			regards, tom lane

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.