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SubjectRe: [reiserfs-dev] Re: Ext2 directory index: ALS paper and benchmarks
Ragnar Kjørstad wrote:

>On Sat, Dec 08, 2001 at 12:01:20AM +0300, Hans Reiser wrote:
>>>In the cases I've studied more closely (e.g. maildir cases) the problem
>>>with reiserfs and e.g. the tea hash is that there is no common ordering
>>>between directory entries, stat-data and file-data.
>>>When new files are created in a directory, the file-data tend to be
>>>allocated somewhere after the last allocated file in the directory. The
>>>ordering of the directory-entry and the stat-data (hmm, both?) are
>>no, actually this is a problem for v3. stat data are time of creation
>>ordered (very roughly speaking)
>>and directory entries are hash ordered, meaning that ls -l suffers a
>>major performance penalty.
>Yes, just remember that file-body ordering also has the same problem.
>(ref the "find . -type f | xargs cat > /dev/null" test wich I think
>represent maildir performance pretty closely)
So is this a deeply inherent drawback of offering readdir name orders
that differ hugely from time of creation order?

The advantages of sorting for non-linear search time are obvious.....

I suppose we could use objectids based on the hash of the first
assigned filename plus a 60 bit global to the FS counter....

but it is too many bits I think. I think that using substantially less
than the full hash of the name that is used for directory entry keys
doesn't work.... Comments welcome.


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