On Wed, Jan 4, 2017 at 12:22 PM, Thomas Munro
<thomas.mu...@enterprisedb.com> wrote:
> (replay_lag - (write_lag / 2) may be a cheap proxy
> for a lag time that doesn't include the return network leg, and still
> doesn't introduce clock difference error)

(Upon reflection it's a terrible proxy for that because of the mix of
write/flush work done by WAL receiver today, but would improve
dramatically if the WAL writer were doing the flushing.  A better yet
proxy might involve also tracking receive_lag which doesn't include
the write() syscall.  My real point is that there are ways to work
backwards from the two-way round trip time to get other estimates, but
no good ways to undo the damage that would be done to the data if we
started using two systems' clocks.)

Thomas Munro

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