Merge lp:~jameinel/bzr/2.3-get-parent-map-faster into lp:bzr/2.3

[John A Meinel]

Speed up ``Repository.get_parent_map`` by about 10%.

This is just a quick drive-by fix that I discovered while playing with Repository.get_parent_map.

This is a server-side fix. It just changes one line from:
small_set.difference_update(large_set)

to

small_set = small_set.difference(large_set)

The former always has to iterate all of its parameter, while the later can notice that 'small_set' is smaller, and do a [x for x in small if x not in large]

Using the improved client, it drops the time from about 26s down to about 23s. Which is 10-15% of the time spent discovering. Not world changing, but a very easy fix, as well. The time spent without my get_parent_map client fixes is about 158s down to 155s. So still about 3s overall.

Much more of an issue with the new code, though. :)

[Jelmer Vernooij (jelmer)]

review: Approve

[John A Meinel (jameinel)]

sent to pqm by email

=== modified file 'bzrlib/smart/repository.py'
--- bzrlib/smart/repository.py	2010-11-16 06:06:11 +0000
+++ bzrlib/smart/repository.py	2011-09-01 15:13:24 +0000
@@ -236,7 +236,7 @@
                 next_revs = set()
                 break
             # don't query things we've already queried
-            next_revs.difference_update(queried_revs)
+            next_revs = next_revs.difference(queried_revs)
             first_loop_done = True
 
         # sorting trivially puts lexographically similar revision ids together.
 
=== modified file 'doc/en/release-notes/bzr-2.3.txt'
--- doc/en/release-notes/bzr-2.3.txt	2011-08-20 09:28:27 +0000
+++ doc/en/release-notes/bzr-2.3.txt	2011-09-01 15:13:24 +0000
@@ -87,6 +87,11 @@
 .. Improvements to existing commands, especially improved performance 
    or memory usage, or better results.
 
+* Tweak an RPC implementation for ``Repository.get_parent_map``, it was
+  doing an inefficient ``small_set.difference_update(large_set)`` when we
+  can do ``small_set = small_set.difference(large_set)``. This speeds up
+  discovery time by about 10%. (John Arbash Meinel)
+
 Bug Fixes
 *********