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On 8/9/2012 9:50 AM, John Simpson wrote:
On 2012-08-08, at 2132, Eric Shubert wrote:
#define MAX_USERS_PER_LEVEL 100
...
In an ext3 environment, it could be set (by the admin) to 3 (ext3
supports 32000 subdirectories), and with ext4 it could be set to 6 (ext4
supports 64000). These settings would for the most part disable hashed
directories, while still allowing hashes should the filesystem limits be
approached. Of course, a default value in dir_control could still be 100,
which would maintain former behavior. If this were done, the
--disable-users-big-dir option should probably be changed to
--allow-single-digit-users as well. ;)
Please let me know what the prospects of such changes are. If it doesn't
look like anything that might ever happen in this area, I just may patch the
vauth.h file to be 3 and call it done.
The filesystem's limit on how many entries can exist in a directory is not
the only issue... the other issue is performance.
On most filesystems (including ext2/3/4), in order to find a particular file
within a directory, the kernel has to do a linear search on the contents. It
can take longer to do a linear search across 30K items than it does to search
through 100 entries, open a new directory, and do a second search through 100
entries. This isn't an issue for filesystems which implement directories as
binary trees instead of linear lists.
Personally, I don't build servers without both hashing options enabled. The
hashing doesn't affect small machines (or small domains) because it doesn't
kick in until a certain number of domains or mailboxes exist. And if the
server becomes busy after the fact, the hashing code kicks in when needed and
keeps mailbox access from being slow.
The scripts that I write which access the mailboxes all use vdominfo or
vuserinfo (or the qmail virtualdomains and users/assign files, and the
domain's vpasswd.cdb file) to locate the directories, rather than making
assumptions about where a particular domain or mailbox might be on the disk.
This way I'm using the same exact method that qmail uses to deliver mail, so
I know I'm ending up in the right place.
If I'm not mistaken, the limitation on single-character mailbox names has
something to do with how the hashing is implemented. The hash directories all
have single-digit or single-letter names, and if a mailbox exists with the
same name, it causes problems (or at least confusion.) Personally, I always
thought they should have given the hash directories names which aren't used
in SMTP address, like ,0 or ,a, but that's not how it was originally
written.
John has basically said everything I was going to :) The only thing I would
mention is that the 5.4.32 and 5.4.33 both include changes that re-populate old
hash directories that have been made lighter by user deletion. It's the
backfill feature.
- --
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Matt Brookings m...@inter7.com GnuPG Key 5F3258AD
Software developer Systems technician
Inter7 Internet Technologies, Inc. (815)776-9465
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