slow nnimap expiry (dubious patch)

[John Magorrian <john.magorrian@ml1.net>]

I've just upgraded from Gnus 5.11 and notice that NoGnus is unusably
slow at expiring msgs from my imap inbox.  Here's my set up:

  (setq gnus-total-expirable-newsgroups "INBOX$\\|personal$\\|...."
        nnmail-expiry-wait 'immediate
        nnmail-expiry-target 'my-gnus-expiry-target)

The reason for this slowness was isolated by Bjørn Mork almost a year
ago (http://article.gmane.org/gmane.emacs.gnus.general/74617): if a
group has only two articles with UIDs 1 and 9999, say, then Gnus will
try to expire all articles in the range 2..9998.  In response,

Lars Magne Ingebrigtsen <larsi@gnus.org> writes:
>
> Gnus know nothing about what articles exist on the server -- just which
> articles that it hasn't read, and the (low . high) range is.  (This
> could be fixed, of course, but it hasn't.)
>
> So looping over `gnus-list-of-read-articles' is a bad idea, since it can
> be monstrously huge, as you've seen, and should be avoided.  I haven't
> looked at the total-expire code, but does it really need to do that?

Here is a quick-and-dirty patch that seems to solve the problem (for
nnimap at least) by modifying 'nnimap-request-expire-articles' to ask
the server what articles it knows about.  I don't think this is an ideal
solution and I'm not even sure it's correct.  Are there any alternative
workarounds for those of us who like Gnus' idea of expiring articles,
but whose IMAP inboxes have vast voids in their UID distributions?

John



From 3cb9f595503fc88aa54b42c88c8c7461e9733187 Mon Sep 17 00:00:00 2001
From: John Magorrian <john.magorrian@ml1.net>
Date: Sun, 6 Nov 2011 21:33:55 +0000
Subject: [PATCH] An attempt at speeding up nnimap expiry.

nnimap.el (nnimap-request-expire-articles): take intersection of
'articles' argument with the article list fetched from IMAP server.
---
 lisp/nnimap.el |   23 +++++++++++++++++++++++
 1 files changed, 23 insertions(+), 0 deletions(-)

diff --git a/lisp/nnimap.el b/lisp/nnimap.el
index cda17ba..9fec178 100644
--- a/lisp/nnimap.el
+++ b/lisp/nnimap.el
@@ -860,6 +860,29 @@ textual parts.")
 
 (deffoo nnimap-request-expire-articles (articles group &optional server force)
   (setq group (nnimap-decode-gnus-group group))
+
+  ;; Filter out any non-existent articles from 'articles'.
+  ;; Ask the server for a list of articles it knows about (the following code
+  ;; snippet is copied from nnimap-request-group) and then take intersection
+  ;; with 'articles'.
+  (let ((genuine-articles
+         (with-current-buffer (nnimap-buffer)
+           (erase-buffer)
+           (let ((marks)
+                 (group-sequence
+                  (nnimap-send-command "SELECT %S" (utf7-encode group t)))
+                 (flag-sequence
+                  (nnimap-send-command "UID FETCH 1:* FLAGS")))
+             (setf (nnimap-group nnimap-object) group)
+             (nnimap-wait-for-response flag-sequence)
+             (setq marks
+                   (nnimap-flags-to-marks
+                    (nnimap-parse-flags
+                     (list (list group-sequence flag-sequence
+                                 1 group "SELECT")))))
+             (cadr (car marks))))))
+    (setq articles (gnus-sorted-intersection articles genuine-articles)))
+
   (cond
    ((null articles)
     nil)
-- 
1.7.2.5