Re: pg_receivexlog --status-interval add fsync feedback

On 09/29/2014 01:13 PM, furuyao@pm.nttdata.co.jp wrote:
>> I don't understand what this patch does. When would you want to use
>> the new --reply-fsync option? Is there any reason *not* to use it?
>> In other words, do we need an option for this, couldn't you just
>> always send the feedback message after fsync?
>
> Thanks for the comment.
>
> --reply-fsync option is intended for use in synchronous mode.
>
> By specifying -F option and --slot option, process calls fsync() when
> it received the WAL, and flush location would be set in feedback
> message.
>
> Interval of sending feedback message depends on -s option in this
> state,  so in the case of synchronous mode, waiting for feedback
> message would occure.
>
> therefore, --reply-fsync option is necessary. because it can send the
> feedback message after fsync without waiting for the interval of -s
> option.
>
> The reason for not sending the feedback message after fsync without
> waiting for the interval of -s option always, is to answer the needs
> who want to use fsync only (NOT using synchronous mode).

I still don't get it. AFAICS there are two ways to use pg_receivexlog. 
Either you use it as a synchronous standby, or not.

What set of options would you pass if you want to use it as a 
synchronous standby? And if you don't? Could we just have a single 
"--synchronous" flag, instead of -F and --reply-fsync?

- Heikki