On Wednesday, May 24, 2017 9:38:36 PM EDT Tsunakawa, Takayuki wrote:
> The clients will know the change of session_read_only when they do
> something that calls RecoveryInProgress(). Currently,
> RecoveryInProgress() seems to be the only place where the sessions
> notice the promotion, so I set session_read_only to the value of
> default_transaction_read_only there. I think that there is room for
> discussion here. It would be ideal for the sessions to notice the
> server promotion promptly and notify the clients of the change. I
> have no idea to do that well.
My original patch did that via the new SendSignalToAllBackends() helper,
which is called whenever the postmaster exits hot stanby.
I incorporated those bits into your patch and rebased in onto master.
Please see attached.
FWIW, I think that mixing the standby status and the default
transaction writability is suboptimal. They are related, yes, but not
the same thing. It is possible to have a master cluster in the
read-only mode, and with this patch it would be impossible to
distinguish from a hot-standby replica without also polling
pg_is_in_recovery(), which defeats the purpose of having to do no
database roundtrips.
Elvis
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