Re: Is full_page_writes=off safe in conjunction with

Hannu Krosing wrote:
> ?hel kenal p?eval, L, 2006-04-15 kell 11:49, kirjutas Tom Lane:
> > Hannu Krosing <hannu@skype.net> writes:
> > > If I'm desperate enough to get the 2x reduction of WAL writes, I may
> > > even write my own backup solution.
> > 
> > Given Florian's concern, sounds like you might have to write your own
> > kernel too.  In which case, generating a variant build of Postgres
> > that allows full_page_writes to be disabled is certainly not beyond
> > your powers.  But for the ordinary mortal DBA, I think this combination
> > is just too unsafe to even consider.
> 
> I guess that writing our own pg_tar, which cooperates with postgres
> backends to get full pages, is still in the realm of possible things,
> even on kernels which dont guarantee atomic visibility of write() calls.
> 
> But until such is included in the distribution it is a good idea indeed
> to disable full_page_writes=off when doing PITR.

The cost/benefit of that seems very discouraging.  Most backup
applications allow for a block size to be specified, so it isn't
unreasonable to assume that people who really want PITR and
full_page_writes can easily set the block size to 8k.  However, I don't
think we are going to allow that to be configured --- you would have to
hack up our backend code to allow the combination.

--  Bruce Momjian   http://candle.pha.pa.us EnterpriseDB    http://www.enterprisedb.com
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