> If not, i know that ext3 can have ten of thousands files in a directory.
> But commande like 'ls' will become slower and slower ...
> Is this also slowing mysql ?
I believe it would have to. There is a patch somewhere (I don't know
if it's maintained) for adding indexed directories to ext2/ext3 to
help this problem, or you could use a different filesystem, such as
ReiserFS that indexes directories out of the box. In an environment
where directory accesses far outnumber directory modifications, you
should see a good improvement if you have 20K files in the directory.
('ls' slows down for reasons besides reading the directory; it usually
sorts its output, and it's often set up to guess file type for each of
the files. Turn those off and it usually goes quite quickly.)