bundle2: implement consume() API on unbundlepart
We want bundle parts to not be seekable by default. That means
eliminating the generic seek() method.
A common pattern in bundle2.py is to seek to the end of the part
data. This is mainly used by the part iteration code to ensure
the underlying stream is advanced to the next bundle part.
In this commit, we establish a dedicated API for consuming a
bundle2 part data. We switch users of seek() to it.
The old implementation of seek(0, os.SEEK_END) would effectively
call self.read(). The new implementation calls self.read(32768)
in a loop. The old implementation would therefore assemble a
buffer to hold all remaining data being seeked over. For seeking
over large bundle parts, this would involve a large allocation and
a lot of overhead to collect intermediate data! This overhead can
be seen in the results for `hg perfbundleread`:
! bundle2 iterparts()
! wall 10.891305 comb 10.820000 user 7.990000 sys 2.830000 (best of 3)
! wall 8.070791 comb 8.060000 user 7.180000 sys 0.880000 (best of 3)
! bundle2 part seek()
! wall 12.991478 comb 10.390000 user 7.720000 sys 2.670000 (best of 3)
! wall 10.370142 comb 10.350000 user 7.430000 sys 2.920000 (best of 3)
Of course, skipping over large payload data isn't likely very common.
So I doubt the performance wins will be observed in the wild.
Differential Revision: https://phab.mercurial-scm.org/D1388
$ hgcommit() {
> hg commit -u user "$@"
> }
$ hg init clhead
$ cd clhead
$ touch foo && hg add && hgcommit -m 'foo'
adding foo
$ touch bar && hg add && hgcommit -m 'bar'
adding bar
$ touch baz && hg add && hgcommit -m 'baz'
adding baz
$ echo "flub" > foo
$ hgcommit -m "flub"
$ echo "nub" > foo
$ hgcommit -m "nub"
$ hg up -C 2
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo "c1" > c1
$ hg add c1
$ hgcommit -m "c1"
created new head
$ echo "c2" > c1
$ hgcommit -m "c2"
$ hg up -C 2
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ echo "d1" > d1
$ hg add d1
$ hgcommit -m "d1"
created new head
$ echo "d2" > d1
$ hgcommit -m "d2"
$ hg tag -l good
fail with three heads
$ hg up -C good
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg merge
abort: branch 'default' has 3 heads - please merge with an explicit rev
(run 'hg heads .' to see heads)
[255]
close one of the heads
$ hg up -C 6
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ hgcommit -m 'close this head' --close-branch
succeed with two open heads
$ hg up -C good
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ hg up -C good
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg merge
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hgcommit -m 'merged heads'
hg update -C 8
$ hg update -C 8
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
hg branch some-branch
$ hg branch some-branch
marked working directory as branch some-branch
(branches are permanent and global, did you want a bookmark?)
hg commit
$ hgcommit -m 'started some-branch'
hg commit --close-branch
$ hgcommit --close-branch -m 'closed some-branch'
hg update default
$ hg update default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
hg merge some-branch
$ hg merge some-branch
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
hg commit (no reopening of some-branch)
$ hgcommit -m 'merge with closed branch'
$ cd ..