From: Francis Cianfrocca <garbagecat10@...>
Date: 2006-08-12T21:27:55+09:00
Subject: Re: Looking for a Fast Persistent Store

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On 8/12/06, Bob Hutchison <hutch@recursive.ca> wrote:
>
>  Sorry, jargon from 3 decades ago. External fragmentation, in this
> case is the disk space wasted due to small files being put into a
> larger segment (e.g. 1k file in a 4k disk segment is a 3k loss of
> space (external fragmentation)). Things like Perst, qdbm, Purple,
> SQLite-as-persistent-store will avoid almost all external
> fragmentation, at the cost of internal fragmentation. In the case of
> the file system, there isn't any space wasted *within* the 1k file,
> but the persistent stores all have this problem (and you'll see them
> talking about free space management, best-fit, first-fit, garbage
> collection, and so on).
>
> Cheers,
> Bob


That's a pretty constant tradeoff, speed for space, and it shows up in many
different ways. I'm convinced that's why there's no single answer to this
problem- every application will need different optimizations. However, this
is somewhat less true than it once was, for two reasons: journaling
filesystems, and the fact that disk storage is still getting cheaper every
year at a rapid rate- it's the only element in the computing chain that
still is. So my inclination (subject to change depending on the particular
case) is to waste space if it will save time (development time and/or
runtime).

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