LDA Indexing
============

LDA updates the main index file while message is being saved. This is useful
with <mbox> [MailboxFormat.mbox.txt] format, especially if
'mbox_very_dirty_syncs=no'. With <Maildir> [MailboxFormat.Maildir.txt] the
benefits of this are pretty small.

LDA also updates cache file, which can be very useful with all mailbox formats.
It means that when IMAP client wants to fetch the message's metadata (e.g. some
header fields) they're already found from the cache file and Dovecot doesn't
have to open and parse the message file. There are some tradeoffs though:

 * LDA indexing wastes disk I/O because it has to open and update index files
 * LDA indexing saves disk I/O because it already has the message body in
   memory, so it doesn't need to read it from disk.
 * IMAP indexing wastes disk I/O because it has to open and read message files
 * IMAP indexing may save disk I/O because IMAP process always has index files
   opened, and many IMAP clients are configured to download all new message
   bodies anyway, so the second time message bodies are read they're already in
   memory

So it depends on IMAP client if it's faster to use LDA or IMAP time indexing.
In any case the user experience is typically faster with LDA indexing, because
the message list metadata can be returned faster when it's pre-indexed.

See <IndexFiles.txt> for more information about what the index files contain.

(This file was created from the wiki on 2010-07-02 21:30)
