Re: [reiserfs-dev] Re: Ext2 directory index: ALS paper and benchmarks

[Hans Reiser <reiser@namesys.com>]

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.)
>
>--
>Daniel
>
>
And how large is the dcache and all the inodes?  I believe large 
directory plus small file performance is heavily affected by the 
enormous size of struct inode and all the other per file data.  


Hans