nnimap summary generation slowness

[Olaf Klischat]

My "INBOX" IMAP folder on my mail server has 313 messages in it.

In the group buffer I hit "- SPC" (i.e. (gnus-topic-read-group t)) on
the folder.

Ethereal show this chatter on the IMAP connection:

10307 UID SEARCH UNSEEN UNDELETED
* SEARCH 60204 60205 60206
10307 OK Completed
10308 UID SEARCH SEEN
* SEARCH 50683 50830 [...308 numbers...] 60148 60180 60203
10308 OK Completed
10309 UID SEARCH FLAGGED
* SEARCH
10309 OK Completed
10310 UID SEARCH ANSWERED
* SEARCH
10310 OK Completed
10311 UID SEARCH KEYWORD gnus-save
* SEARCH
10311 OK Completed
10312 UID SEARCH KEYWORD gnus-forward
* SEARCH
10312 OK Completed
10313 UID SEARCH RECENT
* SEARCH 60204 60205 60206
10313 OK Completed

It takes less than a second to complete. Then, Gnus asks:

"How many articles from nnimap+server:INBOX (default 9521):"

Obviously, 9521 is the size of the interval 50683...60203 (why didn't
it just count the numbers returned to the "UID SEARCH SEEN" command to
get the *correct* number of messages?).

Anyway, I hit ENTER to see all messages.

Another conversation with the server takes place, again just fractions
of a second long:

10314 UID SEARCH UID 50683:60203
* SEARCH 50683 50830 [...308 numbers...] 60148 60180 60203
10314 OK Completed

After that, Gnus eats lots of CPU time for ~5 minutes without either
updating the UI or sending/receiving a single byte to/from the IMAP
server. Then, the summary buffer appears, with the 313 messages in it.

Obviously, there's a lot of air somewhere in there waiting to be
squeezed out.

Olaf