Re: BBU Cache vs. spindles

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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.

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

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