First draft of logging functionality.

[David Bremner]

On Tue, 12 Oct 2010 13:38:42 +0200, Michal Sojka <sojkam1 at fel.cvut.cz> wrote:
> 
> Why multiple log files? You may have the buffers for message logs in
> memory, right?

Well, maybe one log for tag operations, one for adding messages, etc... 
But it is easy enough to mark log entries by what they are.

> 
> Another thing to keep in mind is how it will behave with 'notmuch
> restore'. If do dump followed by resore you will have a very long log
> with no useful information in it. Some optimization may be employed here.
> 

Yes. This seems hard to optimize internally, but I was thinking of some
"log compression" function that comes up with a minimal equivalent set
of operations. I had in mind that this could be used to sync:
concatenate all the logs, and then compress to a minimal set of
operations.  This is still not completely thought out...
Another issue is that the buffer could get rather big during a restore,
but this is presumably fixable by flushing it if it gets too large.

All the best,

David