[MlMt] MailMate and Time Machine

Glenn Parker glenn.parker at comcast.net
Wed Oct 21 22:20:46 EDT 2020

On 21 Oct 2020, at 13:56, Steven M. Bellovin wrote:

> I've had to disable Time Machine backups of the directories
> containing my IMAP messages—I was getting at most two
> backups per day because each one took so long. Some of
> it, I'm sure, is because I have about a million messages, but I don't 
> think that that's the whole story—my backup laptop, which has most 
> of those messages but does not normally
> run MailMate except periodically when I want it to catch up, can 
> handle Time Machine reasonably well.
> The issue, then, would seem to be something about messages
> being added to or deleted from some mail folders, possibly
> propagating up the directory tree. Is that right? Is there some 
> organizational pattern I could use that would cut the time?
> Is it, for example, that I have too many messages in certain folders?

I exclude ~/Library/Application Support/MailMate/Database.noindex from 
my Time Machine backups. It makes a real difference (measured using 
*BackupLoupe 2*).

I’m pretty sure the database index files can (and should) be 
reconstructed after a file recovery. These database files get pretty 
large (mine total to about 600MB for 49,000 messages). Each of the many 
index files covers *all* the messages in the system, and each can be 
updated after any message is received, moved or expunged. As a result, 
Time Machine records a fair amount of this database (around 500MB for 
me) on every backup cycle.

In contrast, the message contents are stored as single files under 
~/Library/Application Support/MailMate/Messages.noindex. Time Machine 
uses storage proportional to the size of the messages that change during 
each backup cycle.

Glenn P. Parker
glenn.parker at comcast.net
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