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NetWin Database Mode (g_maildir_netwin "true").
- How it works
- What advantages does it have
- What disadvantages does it have
- How do I turn it on
- Utility commands
Warning! This feature is in ALPHA test stage, do not use at this time!
How it works:
Instead of storing each mail message as an individual file messages are stored in 'bucket' files which contain many messages, an index file contains a list of the contents of all of the bucket files.
So a folder with 100 mail messages in it might look like this:
28/09/2005 05:15 p.m. 1,120 bkt.idx
28/09/2005 05:15 p.m. 0 bkt.lock
28/09/2005 05:15 p.m. 7,578 bkt_0.bkt
28/09/2005 05:15 p.m. 4,450 bkt_0.head
26/09/2005 05:09 p.m. 442,871 bkt_1127711348.bkt
26/09/2005 05:08 p.m. 31,668 bkt_1127711348.headWhen a bucket file is partly empty due to deleted messages it is re-written.
New mesesages always go to bucket zero.
What advantages does it have
- When accessing lots of little files the disk IO is greatly reduced, and the speed can thus be 2-4 times faster.
- IMAP gets the most noticable speed improvement.
- When backing up a mail partition the operating system has a much simpler job, this can make backup runs 4-14 times faster.
- Some operating systems either fail completely, or run very badly when a disk has millions of files on it, this reduces this problem drastically.
- If sharing a drive using NFS it should work as long as fcntl locking works on your NFS drives.
What disadvantagese does it have
- It's a new feature which involved massive internal changes to surgemail, there is significant risk that bugs could exist in it.
- It is a lot more complex than the 'file per message' model, so is more prone to bugs.
- You can't manually examine a users mail box and modify files (although there are some commands to let you do this to some extent)
- Message delivery is about 20% slower! (as the indexes are written at delivery time)
How do I turn it on -- (WARNING, THIS FEATURE IS NOT YET SAFE TO USE)
- Make a backup of your mail spool (or mirror it)
- Set the new setting g_maildir_netwin "true"
- Restart surgemail
- An automatic conversion process will start, in addition any mailbox which is accessed will be automatically converted.
- (You can turn it off the same way, change the setting and restart surgemail)
- DO NOT DOWNGRADE TO AN EARLIER VERSION OF SURGEMAIL AFTER CONVERTING :-)
- You can turn it on, on ONE member of a mirrored pair of surgemail servers.
Utility commands.
Command Decription tellmail dir user@domain [folder] Show files in that inbox/folder tellmail ndb_export user@domain foldername destination_path Export files to a directory tellmail ndb_repair user@domain.name Repair index based on bucket files tellmail ndb_convert Start convert process again