Re: btree on disk

This stuff about mbox/maildir is a strawman based upon misrepresentation.

The filesystem tests that I performed were over a decade ago, on FFS and (shudder!) AdvFS. Those filesystems did indeed perform quite poorly once you get to about 1200 files per directory. Modern filesystems do quite a bit better, but they do not eliminate this scaling problem.

I work with mail stores with 6 (soon 7) digit message counts containing multiple GB in a single mailbox. Neither mbox nor maildir fufill that requirement.

I never advocated mbox as a good mailbox format. Let's be clear: I have always hated that format. mbox is the UW imapd default for one reason only: mbox is the default in the default mailer on most UNIX systems. It is otherwise a terrible format, unless you are an oldtimer in the habit of running vi on mailbox files.

There are multiple, widely-distributed, third party implementations of maildir for UW imapd. They are easy to get, and easy to add. They are less than fully satisfactory. I do not believe than I can do a better job and still comply with DJB's definition of maildir.

To address the technical problems with supporting maildir in IMAP, both Courier (maildir++) and Dovecot extend maildir beyond DJB's definition. To my knowledge, these extensions have not been formally published and accepted as the replacement for DJB's definition. Should that ever change, I will certainly revisit the question of developing and supporting maildir in UW imapd.

UW imapd supports other formats, any of which are superior to mbox. One format, designed in the mid 1990s, easily handles the users with 10MB mailbox attachments on a 20 user system. Its 21st century replacement is extensible, indexed, and directory structured (not one-file/one-message though).

The criticism, noted on the maildir Wikipedia entry about the numerous mutually-incompatible mail store formats used by different mail systems, is valid. However, that does not mean that maildir is the one and only true solution. The developers of various mail stores are all groping for answers for the various technical problems that they face. To a surprising degree they share their findings with each other.

-- Mark --

http://staff.washington.edu/mrc
Science does not emerge from voting, party politics, or public debate.
Si vis pacem, para bellum.
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