MAIL

Determining how many MAIL.BOX databases to place on a server
When a server sends and receives mail, server processes, such as the Router, access the server's MAIL.BOX database, writing messages to it and reading messages from it. Because only one process at a time can access MAIL.BOX, when mail traffic is heavy, access conflicts occur as multiple processes try to access the database simultaneously.

For servers that support a small number of users, access conflicts are rare, and the default of a single MAIL.BOX usually provides an acceptable level of service. However, on servers that support a higher numbers of users, creating an additional MAIL.BOX database can eliminate most access conflicts.

Especially busy servers may benefit from more than two MAIL.BOX databases. Use mailbox statistics to determine whether additional MAIL.BOX databases are indicated. As seen in the following table, separate statistics provide information on the number of access conflicts and the number of total mailbox accesses.
Statistic nameDescription
Mail.Mailbox.AccessesTotal number of times that threads accessed any mailbox on the server.
Mail.Mailbox.AccessConflictsThe number of times that a thread attempting to access a mailbox had to wait because the number of concurrent threads exceeded the number of mailboxes configured.

For example, if there are three mailboxes configured, and there are four concurrent accesses, the conflict count would be incremented.

If the number of access conflicts consistently exceeds two percent of the value of Mail.Mailbox.Accesses, consider creating an additional mailbox.

Mail.Mailbox.CurrentAccessesThe total number of current accesses (for example. a count of 2 would indicate that two threads are accessing mailbox at this time.
Mail.Mailbox.AccessWarningsThe number of times that the number of threads accessing the mailbox (that is, the value of Mail.Mailbox.CurrentAccesses) reached one less than the number of configured mailboxes.

For example, the warning count is incremented when two threads attempt to access MAIL.BOX concurrently and there are three mailboxes configured.

If the number of warnings consistently exceeds ten percent of the value of Mail.Mailbox.Accesses, consider creating an additional mailbox.

Mail.Mailbox.MaxConcurrentAccessesThe highest number of current accesses recorded.
By calculating the number of access conflicts as a percentage of total accesses, you can determine whether a server will benefit from the addition of another MAIL.BOX. In general, the number of access conflicts should be no more than two percent of the total number of accesses. However, because some access conflicts may result from unusually high peak loads, there's no need to eliminate all access conflicts. Only when the percentage of access conflicts remains consistently greater than 2 percent is an additional MAIL.BOX database warranted.

Note Mailbox statistics are available only on servers where two or more MAIL.BOX databases are configured. You must restart the server to put into effect any changes to the number of mailboxes.

See also