Re: BBU Cache vs. spindles

Rob Wultsch <wultsch@gmail.com> wrote:

> I would think full_page_writes=off + double write buffer should be
> far superior, particularly given that the WAL is shipped over the
> network to slaves.

For a reasonably brief description of InnoDB double write buffers, I
found this:

http://www.mysqlperformanceblog.com/2006/08/04/innodb-double-write/

One big question before even considering this would by how to
determine whether a potentially torn page "is inconsistent".
Without a page CRC or some such mechanism, I don't see how this
technique is possible.

Even if it's possible, it's far from clear to me that it would be an
improvement.  The author estimates (apparently somewhat loosely)
that it's a 5% to 10% performance hit in InnoDB; I'm far from
certain that full_page_writes cost us that much.  Does anyone have
benchmark numbers handy?

-Kevin