Jeff Frost <jeff@frostconsultingllc.com> writes:
> Why does it request it twice?
I think the reason is that the rollforward cycle is
fetch next segment into RECOVERYXLOG
process segment
unlink RECOVERYXLOG
and only when the "fetch" step fails does it realize it's done. So then
it has to figure out which segment it wants to start extending and fetch
that into the real name of the segment.
We could probably rejigger this to avoid a duplicate fetch in common
cases, but I'm worried that we couldn't guarantee it in every case ---
edge cases like the last valid xlog record ending right at a segment
boundary might be trouble. If the recovery script has to handle the
situation sometimes, it's probably best to make it do so on a regular
basis --- would you like to have only found out about this when you were
trying to revive your database at 4AM?
regards, tom lane