ANNOTATE: Optimize mass-delete of a message annotation

[alecpl]

Let's say I have a mailbox with some messages that have a /comment annotation. I don't really know which ones. For "Remove all comments from messages" action I'd just do:

a26 STORE 1:* ANNOTATION (/comment (value.priv NIL))
* 1 FETCH (FLAGS () MODSEQ (187))
* 2 FETCH (FLAGS () MODSEQ (188))
* 3 FETCH (FLAGS () MODSEQ (189))
* 4 FETCH (FLAGS () MODSEQ (190))
a26 OK Completed

There's one problem I see here. It will "modify" all messages including these that do not have the annotation.

This becomes problematic when you fetch the last changes.

a27 FETCH 1:* (ANNOTATION (/comment value.priv)) (CHANGEDSINCE 186)
* 1 FETCH (MODSEQ (187) ANNOTATION (/comment (value.priv NIL)))
* 2 FETCH (MODSEQ (188) ANNOTATION (/comment (value.priv NIL)))
* 3 FETCH (MODSEQ (189) ANNOTATION (/comment (value.priv NIL)))
* 4 FETCH (MODSEQ (190) ANNOTATION (/comment (value.priv NIL)))
a27 OK Completed (0.000 sec)

If the mailbox has a lot of messages both can be unnecessarily slow.