Re: [rfc] Near-constant time directory index for Ext2

From: Jamie Lokier (
Date: Wed Feb 21 2001 - 18:26:48 EST

Martin Mares wrote:
> Hello!
> > True. Note too, though, that on a filesystem (which we are, after all,
> > talking about), if you assume a large linear space you have to create a
> > file, which means you need to multiply the cost of all random-access
> > operations with O(log n).
> One could avoid this, but it would mean designing the whole filesystem in a
> completely different way -- merge all directories to a single gigantic
> hash table and use (directory ID,file name) as a key, but we were originally
> talking about extending ext2, so such massive changes are out of question
> and your log n access argument is right.

A gigantic hash table has serious problems with non-locality of
reference. Basically any regular access pattern you started with is
destroyed. This is a problem with pageable RAM, let alone disks with
millisecond seek times.

-- Jamie
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This archive was generated by hypermail 2b29 : Fri Feb 23 2001 - 21:00:26 EST