sendmail, 4th Edition

Class Name Hashing Algorithm

When comparing a token in the workspace to a list of words in a class array, sendmail tries to be as efficient as possible. Instead of comparing the token to each word in the list, one by one, it simply looks up the token in its internal string pool. If the token is in the pool and if the pool listing is marked as belonging to the class being sought, a match is found.

The comparison of tokens to entries in the string pool is case-insensitive. Each token is converted to lowercase before the comparison, and all strings in the string pool are stored in lowercase.

Because strings are stored in the pool as text with a type, the same string value can be used for different types with no conflict. For example, the symbolic name of a delivery agent and a word as a class macro’s value can be identical, yet they will still be separate entries in the string pool.

The sendmail program uses a simple hashing algorithm to ensure that the token is compared to the fewest possible strings in the string pool. In normal circumstances, that algorithm performs its job well. At sites with unusually large classes (perhaps a few thousand hosts in a class of host aliases), it might be necessary to tune the hashing algorithm. The code is in the file stab.c with the sendmail source. The number of hash buckets is set by the constant STABSIZE.

As an alternative to very full classes, sendmail offers database maps (Enable at Compile Time on page 879). No information is currently available ...