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

Dovecot v1.0's deliver 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.

Dovecot v1.1+ deliver updates also 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 2009-10-16 04:42)