[notmuch] Idea for storing tags

[Carl Worth]

On Tue, 12 Jan 2010 11:19:09 +1300, martin f krafft <madduck at madduck.net> wrote:
> 1. External database, which has the downside of not being
>    synchronisable with standard IMAP, like the rest of your mail
>    (assuming you use IMAP). Also, it's possible for mailstore and
>    database to get out of sync.

Yes. This approach requires some external means of synchronizing the
tags from one system to another.

I don't understand what it would mean to have the mailstore and the
database out of synch here. This approach doesn't have the tags in the
mailstore by definition, right?

> How about using pseudo-mails stored in Maildir and synchronised by
> IMAP? E.g. every folder could have a subfolder .TAGS and if we find
> a way to smartly pair messages between parent and subfolder, we'd
> have a tag store alongside the mailstore it refers to, but without
> the danger of leakage, and without having to rewrite messages.
...
> Anyway, the idea is out now. Thoughts?

There are a couple of problems that I don't see addressed at all with
this approach. The first is that there's not a one-to-one mapping
between messages and files in the mail store. (I'm CCed on a lot of list
mail meaning that I have multiple files in my mail store for a single
message.)

Second, the only reason I would be interested in synchronizing mail
between two systems is so that I could manipulate the tag data in
multiple places, (that is, remove the "unread" tag whether on my
network-disconnected laptop or via web-mail when away from my
laptop). Using imap for synchronizing a file of tags within the mail
store gives you no mechanism for doing any sort of conflict resolution,
right? (Which I think in almost all cases is going to be quite trivial
if there's a chance for a program to resolve it.)

So it sounds to me like we're going to need *something* custom for doing
the synchronization, (to handle modifications on both ends). At which
point there's only disadvantages to keeping the data inside the
mailstore, and there's also no disadvantage left to keeping the data
inside a database. [*]

[*] Though, I think a plain-text file with tags managed with something
like git (and perhaps a custom merger) could save a lot of work. Or
perhaps a plain-text journal of tag manipulations on either end that
could be replayed on the other.

-Carl
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