I have spotted the biggest bottleneck in "bdiff.c". Actually it was
pretty easy to find after I recompiled the python interpreter and
mercurial for profiling.
In "bdiff.c" function "equatelines" allocates the minimum hash table
size, which can lead to tons of collisions. I introduced an
"overcommit" factor of 16, this is, I allocate 16 times more memory
than the minimum value. Overcommiting 128 times does not improve the
performance over the 16-times case.
% init foo-base
% create alpha in first repo
adding alpha
% clone foo-base to foo-work
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
% create beta in second repo
adding beta
% create gamma in first repo
adding gamma
% pull into work and merge
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
% revert to changeset 1 to simulate a failed merge
2 files updated, 0 files merged, 0 files removed, 0 files unresolved