Re: [exim] Exim 5 Wishlist

On Fri, Feb 16, 2007 at 04:56:53AM +0800, W B Hacker wrote:
> Richard Pitt wrote:
> > SQL generally requires far
> > more resources for similar performance - especially with "blobs" of any
> > size.
>
> Not 'generally'. 'Always'. And by a large margin.
>
> At the end of the day any DB must *also* map to the underlying fs -
> and not just the raw data - but all of its own overhead, logs, checks
> and balances, bells and whistles.

You're oversimplifying here. Kernels have the ability to switch off
caching (O_DIRECT, etc), metadata-updates, and similar, for specific
files, and database servers generally use those APIs.

It's also perfectly possible in some cases to run a database directly on
a raw device ('/dev/XXX'), and bypass the filesystem entirely.

Finally, if you run a mail store on a filesystem, you usually require
many files -- exim requires two files per mail in the mail store. Most
database systems dump all their tables in one file, so the stress on the
filesystem implementation isn't as extensive.

Not that I think using a database server as a mail store is a
particularly good idea, but that's a different matter entirely.

--
<Lo-lan-do> Home is where you have to wash the dishes.
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