On 23/02/15 03:24, Robert Haas wrote:
On Sat, Feb 21, 2015 at 11:29 PM, Petr Jelinek <p...@2ndquadrant.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.
Err yes of course, min not max :)
Would it make sense to require that wal_keep_segments <= wal_min_size?
It would to me, the patch as it stands is confusing in a sense that you
can set min and max but then wal_keep_segments somewhat overrides those.
And BTW this brings another point, I actually don't see check for
min_wal_size <= max_wal_size anywhere in the patch.
--
Petr Jelinek http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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