sendmail Performance Tuning

4.7. Message Store Hashing

As mentioned earlier, many filesystems perform a linear search for file or subdirectory names in a directory. With large numbers of users, this search can present a real performance problem in the /var/mail directory. Even using filesystems that perform hashed directory lookups, having hundreds of thousands, or even millions, of files or subdirectories in a single directory will not work well, or at all. For this reason, it’s a good idea to subdivide a large message store by hashing it.

Support for a simple way of performing this task is provided in the qpopper distribution. One sets a variable called HASH_SPOOL to a numerical value at compile time, and qpopper will use that value and the mailbox name to construct ...