High CPU usage on Tree View with many emails

[Piotr Trojanek]

Hi,

I am trying notmuch + notmuch-emacs version 0.23.5-1~bpo8+1 from
debian jessie backports, and reproduced this issue with both emacs
24.4 (jessie) and 24.5+1-6~bpo8+1 (jessie backports).

When I make a query that gives many results (e.g. "review", which hits
~2200 emails with my Gerrit reviews) and want to display them in Tree
View, the CPU usage stays high for several seconds.

While this happens, the Emacs window flickers, like it was busy with
redisplaying the buffer. If I pull the horizontal scroll of the Emacs
buffer down, I can see that the buffer grows (like messages being
inserted there). The Emacs profiler says that more than 50% of CPU
time is spend in notmuch-tree-insert-forest-thread.

Interestingly, the in the non-tree view the same query is processed in no time.

Any idea?

-- 
Piotr Trojanek