Re: time-delayed standbys

On Wed, Apr 20, 2011 at 11:15 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> I am a bit concerned about the reliability of this approach.  If there
>> is some network lag, or some lag in processing from the master, we
>> could easily get the idea that there is time skew between the machines
>> when there really isn't.  And our perception of the time skew could
>> easily bounce around from message to message, as the lag varies.  I
>> think it would be tremendously ironic of the two machines were
>> actually synchronized to the microsecond, but by trying to be clever
>> about it we managed to make the lag-time accurate only to within
>> several seconds.
>
> Well, if walreceiver concludes that there is no more than a few seconds'
> difference between the clocks, it'd probably be OK to take the master
> timestamps at face value.  The problem comes when the skew gets large
> (compared to the configured time delay, I guess).

I suppose.  Any bound on how much lag there can be before we start
applying to skew correction is going to be fairly arbitrary.

--
Robert Haas
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