| From: | Tatsuo Ishii <ishii(at)sraoss(dot)co(dot)jp> |
|---|---|
| To: | tsunakawa(dot)takay(at)jp(dot)fujitsu(dot)com |
| Cc: | pg(at)fastcrypt(dot)com, tgl(at)sss(dot)pgh(dot)pa(dot)us, robertmhaas(at)gmail(dot)com, laurenz(dot)albe(at)cybertec(dot)at, kommi(dot)haribabu(at)gmail(dot)com, jingwangian(at)gmail(dot)com, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Libpq support to connect to standby server as priority |
| Date: | 2019-01-16 04:42:04 |
| Message-ID: | 20190116.134204.433037985172724288.t-ishii@sraoss.co.jp |
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| Lists: | pgsql-hackers |
>> I'm confused as to how this would work. Who or what determines if the server
>> is a primary or standby?
>
> Overall, the server determines the server role (primary or standby) using the same mechanism as pg_is_in_recovery(), and set the server_role GUC parameter. As the parameter is GUC_REPORT, the change is reported to the clients using the ParameterStatus ('S') message. The clients also get the value at connection.
But pg_is_in_recovery() returns true even for a promoting standby. So
you have to wait and retry to send pg_is_in_recovery() until it
finishes the promotion to find out it is now a primary. I am not sure
if backend out to be responsible for this process. If not, libpq would
need to handle it but I doubt it would be possible.
Best regards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese:http://www.sraoss.co.jp
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