On Mon, Nov 07, 2005 at 11:59:39AM +0100, Paul Dekkers wrote: > >Make sure that you format ext3 partitions with dir_index which improves > >large directory performance. > > ... but decreases read performance in general... at least that is what I > found under RH / Fedora!
Yes, processing directory entries in the order returned by readdir() is slower when dir_index is enabled: https://listman.redhat.com/archives/ext3-users/2004-September/msg00029.html Actually you'd get similar slowdown if you create/delete a lot of files in random order. The speed of readdir() w/ dir_index on a newly populated directory should be similar to the speed of readdir() w/o dir_index on a heavily used mail folder. It would be interesting if you could repeat the measurement with LD_PRELOAD'ing the readdir-sorting library posted in: https://listman.redhat.com/archives/ext3-users/2004-September/msg00025.html > BTW: I found that chaning dir_index with tune2fs didn't work as > expected. If I disabled the dir_indexes, even after a forced fsck, > performance was still slow. Enabling didn't give predictable results > either: I had to specify it with mkfs. Disabling dir_index will not reorder existing directories. Again, the result should be similar to what you'd get after creating/deleting a lot of files in random order, so that the readdir() order no longer matches the disk layout. Also, this read benchmark only models the case when users download every mail in a folder sequentially (like POP3). It does not tell anything about the case when users randomly open files (by explicit filename instead of using readdir()) inside a folder. I think Cyrus uses its own database instead of doing a readdir() even for POP3, so this benchmark may not even match POP3 usage. Gabor -- --------------------------------------------------------- MTA SZTAKI Computer and Automation Research Institute Hungarian Academy of Sciences --------------------------------------------------------- ---- Cyrus Home Page: http://asg.web.cmu.edu/cyrus Cyrus Wiki/FAQ: http://cyruswiki.andrew.cmu.edu List Archives/Info: http://asg.web.cmu.edu/cyrus/mailing-list.html