Re: Redesigning checkpoint_segments

On Sat, Feb 21, 2015 at 11:29 PM, Petr Jelinek <petr(at)2ndquadrant(dot)com> wrote:
> I am wondering a bit about interaction with wal_keep_segments.
> One thing is that wal_keep_segments is still specified in number of segments
> and not size units, maybe it would be worth to change it also?
> And the other thing is that, if set, the wal_keep_segments is the real
> max_wal_size from the user perspective (not from perspective of the
> algorithm in this patch, but user does not really care about that) which is
> somewhat weird given the naming.

It seems like wal_keep_segments is more closely related to
wal_*min*_size. The idea of both settings is that each is a minimum
amount of WAL we want to keep around for some purpose. But they're
not quite the same, I guess, because wal_min_size just forces us to
keep that many files around - they can be overwritten whenever.
wal_keep_segments is an amount of actual WAL data we want to keep
around.

Would it make sense to require that wal_keep_segments <= wal_min_size?

--
Robert Haas
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