Ext3 users - May 2010 - ext3_dx_add_entry: Directory index full!

My log is showing errors like
May  1 05:14:17 corn kernel: [6822807.017625] EXT3-fs warning (device dm-7):
ext3_dx_add_entry: Directory index full!

Judging from the minor device numbers in /dev/mapper, that corresponds to my
mail spool.

My searches suggest that the problem indicates an individual directory
has too many files in it. There does not seem to be a general shortage
of inodes or space. df -i shows IUse of 11% for that partition and df
says 88% of the ~37G is in use.

First question: what happens in these circumstances?  Are files lost?
Search and indexing are inefficient?  The program trying to write the
file gets an error (it's cyrus. 10 seconds after the errors shown above,
the log has "cyrus/master[8178]: process 11850 exited, status 98".
Usually the status is 0.)?

Second: is there a way to find what directory is causing the problem?

Third: How can I fix this?

I'm running a stock Debian Lenny  2.6.26-2-686 kernel.

On 2010-05-02, at 02:57, Ross Boylan wrote:
My log is showing errors like
> May  1 05:14:17 corn kernel: [6822807.017625] EXT3-fs warning (device
dm-7): ext3_dx_add_entry: Directory index full!
> 
> Judging from the minor device numbers in /dev/mapper, that corresponds to
my mail spool.
> 
> My searches suggest that the problem indicates an individual directory
> has too many files in it. There does not seem to be a general shortage
> of inodes or space. df -i shows IUse of 11% for that partition and df
> says 88% of the ~37G is in use.
The directory is probably at least 10M files, though it might also suffer from
the random create/delete cycle of the mail spool directory.
> First question: what happens in these circumstances?  Are files lost?
> Search and indexing are inefficient?
It _should_ be the latter, though I haven't actually looked into it closely.
> Second: is there a way to find what directory is causing the problem?
Patch the error message to print the inode number and dentry name, and submit it
here.
> Third: How can I fix this?
e2fsck -fD on the filesystem (unmounted of course)

Cheers, Andreas