Re: Improve handling of parameter differences in physical replication

On 2020-Feb-27, Peter Eisentraut wrote:

> So this patch relaxes this a bit. Upon receipt of
> XLOG_PARAMETER_CHANGE, we still check the settings but only issue a
> warning and set a global flag if there is a problem. Then when we
> actually hit the resource issue and the flag was set, we issue another
> warning message with relevant information. Additionally, at that
> point we pause recovery, so a hot standby remains usable.

Hmm, so what is the actual end-user behavior? As I read the code, we
first send the WARNING, then pause recovery until the user resumes
replication; at that point we raise the original error. Presumably, at
that point the startup process terminates and is relaunched, and replay
continues normally. Is that it?

I think if the startup process terminates because of the original error,
after it is unpaused, postmaster will get that as a signal to do a
crash-recovery cycle, closing all existing connections. Is that right?
If so, it would be worth improving that (possibly by adding a
sigsetjmp() block) to avoid the disruption.

Thanks,

--
Álvaro Herrera https://www.2ndQuadrant.com/
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