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

>On December 7, 2001 07:03 pm, Ragnar Kjørstad wrote:
>>>With ReiserFS we see slowdown due to random access even with small
>>>directories. I don't think this is a cache effect.
>>I can't see why the benefit from read-ahead on the file-data should be
>>affected by the directory-size?
>>I forgot to mention another important effect of hash-ordering:
>>If you mostly add new files to the directory it is far less work if you
>>almost always can add the new entry at the end rather than insert it in
>>the middle. Well, it depends on your implementation of course, but this
>>effect is quite noticable on reiserfs. When untaring a big directory of
>>maildir the performance difference between the tea hash and a special
>>maildir hash was approxemately 20%. The choice of hash should not affect
>>the performance on writing the data itself, so it has to be related to
>>the cost of the insert operation.
>Yes, I think you're on the right track. HTree on the other hand is optimized
>for inserting in arbitrary places, it takes no advantage at all of sequential
>insertion. (And doesn't suffer from this, because it all happens in cache
>anyway - a million-file indexed directory is around 30 meg.)
someday reiserfs might benefit from inserting more airholes into
directories so that insertion is more efficient.

This may be a significant advantage of Htree.

Yet another feature needed.....:-/


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