Re: BBU Cache vs. spindles

Excerpts from Greg Smith's message of jue oct 21 14:04:17 -0300 2010:

> What I would like to do is beef up the documentation with some concrete
> examples of how to figure out if your cache and associated write path
> are working reliably or not.  It should be possible to include "does
> this handle full page writes correctly?" in that test suite.  Until we
> have something like that, I'm concerned that bugs in filesystem or
> controller handling may make full_page_writes unsafe even with a BBU,
> and we'd have no way for people to tell if that's true or not.

I think if you assume that there are bugs in the filesystem which you
need to protect against, you are already hosed.  I imagine there must be
some filesystem bug that makes it safe to have full_page_writes=on, but
unsafe to have full_page_writes=off; but I'd probably discard those as a
rare minority and thus not worth worrying about.

I agree it would be worth testing though.

--
Álvaro Herrera <alvherre@commandprompt.com>
The PostgreSQL Company - Command Prompt, Inc.
PostgreSQL Replication, Consulting, Custom Development, 24x7 support