[PATCH v3] emacs: Call "notmuch tag" once when applying tag changes to a thread.

[David Edmondson]

Optimize thread tagging by combining all the tagging operations to a
single "notmuch tag" call.

For threads in the order of tens or a hundred inbox tagged messages,
this gives a noticeable speedup. On two different machines, archiving
a thread of about 50 inbox tagged messages goes down from 10+ seconds
to about 0.5 seconds.

The bottleneck is not within emacs; the same behaviour can be observed
in the CLI. This approach has the added benefit of being more
reliable: any of the individual tagging operations might face a locked
database, leading to partial results.

This introduces a limitation to the number of messages that can be
archived at the same time (through ARG_MAX limiting the command
line). While at least on Linux this seems more like a theoretical
limitation than a real one, it could be avoided by archiving at most a
few hundred messages at a time.

Based on code from Jani Nikula <jani at nikula.org>.
---

Batch all thread tagging rather than archive being a special case.

 emacs/notmuch-show.el |   19 ++++++++++---------
 1 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/emacs/notmuch-show.el b/emacs/notmuch-show.el
index 7469e2e..bbba482 100644
--- a/emacs/notmuch-show.el
+++ b/emacs/notmuch-show.el
@@ -1582,16 +1582,17 @@ argument, hide all of the messages."
   (backward-button 1))
 
 (defun notmuch-show-tag-thread-internal (tag &optional remove)
-  "Add tag to the current set of messages.
+  "Add TAG to the current set of messages.
 
-If the remove switch is given, tags will be removed instead of
-added."
-  (goto-char (point-min))
-  (let ((tag-function (if remove
-			  'notmuch-show-remove-tag
-			'notmuch-show-add-tag)))
-    (loop do (funcall tag-function tag)
-	  until (not (notmuch-show-goto-message-next)))))
+If REMOVE is non-nil, TAG will be removed rather than added."
+  (save-excursion
+    (goto-char (point-min))
+    (let ((message-ids
+	  (loop collect (notmuch-show-get-message-id)
+		until (not (notmuch-show-goto-message-next)))))
+      (if message-ids
+	  (notmuch-tag (mapconcat #'identity message-ids " OR ")
+		       (concat (if remove "-" "+") tag))))))
 
 (defun notmuch-show-add-tag-thread (tag)
   "Add tag to all messages in the current thread."
-- 
1.7.8.3