[Dovecot] Maildir unreliability

[Peter Hessler]

On Mon, 25 Oct 2004 03:02:31 +0300
Timo Sirainen <tss at iki.fi> wrote:

:Looks like maildir can't be used very realiably without quite a lot of 
:locking. Writing and scanning the directory would have to be locked, 
:but reading wouldn't (as long as the file hasn't been renamed which 
:would require scanning to find it). So much for "no locks needed"..
:
:The problem is that opendir()/readdir() may temporarily not return some 
:files if there has been changes in the directory since the opendir(). 
:That means Dovecot thinks a message is expunged, while in fact it 
:really isn't, and the next scan would usually show it again.
:
:Currently when that happens, Dovecot usually prints an error message 
:about it and rebuilds indexes. Of course, in real life clients aren't 
:often bombing the same mailbox with tons of changes in multiple 
:connections, which is usually needed to trigger this.
:
:I wrote a test program which tests this:
:
:http://dovecot.org/tmp/readdir.c
:
:I'd like to hear if you can run it in some system without errors. I 
:tested Linux 2.4 and 2.6 with ext2, ext3, xfs and reiser3, Solaris 
:8/ufs and OpenBSD 3.5/sparc64. Only OpenBSD passed the test, but I'm 
:not sure if it's only because the computer was so slow and didn't 
:switch between processes hard enough. I'd be especially interested 
:about FreeBSD and various NFS systems.
:
:If it actually works properly in some systems, I guess I'll make the 
:extra locking configurable.
:

gir.theapt.org:phessler@/usr/home/phessler> ./readdir 
28751: File re-appeared:  -> 983:2,S (2)
4017: File re-appeared:  -> 707:2,S (2)
4017: File re-appeared:  -> 724:2, (2)
4017: File re-appeared:  -> 800:2,S (2)
30179: File re-appeared: 429:2,S -> 429:2, (2)

This is on OpenBSD/macppc -current, the partition is mounted as:
/dev/wd0h on /usr/home type ffs (local, noatime, nodev, nosuid, softdep)



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