[Pgpool-hackers] Replication node failure == aborted transaction... bug?

[Tatsuo Ishii]

> I noticed that if i take one of the replication nodes offline, and if
> the failure is noticed from a client transaction instead of a health
> check, the failure propagates up to the client and causes an exception
> (which in turn would likely cause a 500 Internal Server Error for
> a visitor to a postgres-backed webapp).  Shouldn't it be the case that
> the error results in the silent (to the frontend, anyway) degradation
> of the node and another attempt at the transmission of the request?

Yeah, it's desirable but pretty hard to implement.

For example, consider load balanced SELECT. If a node goes offline
while SELECT result is being returned to frontend, pgpool needs to
remember all the rows which it has been already received and restart
the transmission from the point against the different node.
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese: http://www.sraoss.co.jp