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: laurenz.albe@cybertec.at
Cc: Jing Wang <jingwangian@gmail.com>, Pg Hackers <pgsql-hackers@postgresql.org>, "Tsunakawa, Takayuki" <tsunakawa.takay@jp.fujitsu.com>
Date: 2018-07-16T08:14:57Z
Lists: pgsql-hackers 
On Wed, Jul 11, 2018 at 6:00 PM Haribabu Kommi <kommi.haribabu@gmail.com>
wrote:

>
>
> On Wed, Jul 4, 2018 at 11:14 PM Laurenz Albe <laurenz.albe@cybertec.at>
> wrote:
>
>> Haribabu Kommi wrote:
>>
>>
> - I think the construction with "read_write_host_index" makes the code
>> even more
>>   complicated than it already is.
>>
>>   What about keeping the first successful connection open and storing it
>> in a
>>   variable if we are in "prefer-read" mode.
>>   If we get the read-only connection we desire, close that cached
>> connection,
>>   otherwise use it.
>>
>
> Even if we add a variable to cache the connection, I don't think the logic
> of checking
> the next host for the read-only host logic may not change, but the extra
> connection
> request to the read-write host again will be removed.
>

I evaluated your suggestion of caching the connection and reuse it when
there is no
read only server doesn't find, but I am thinking that it will add more
complexity and also
the connection to the other servers delays, the cached connection may be
closed by
the server also because of timeout.

I feel the extra time during connection may be fine, if user is preferring
the prefer-read
mode, instead of adding more complexity in handling the cached connection?

comments?

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.