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
Minimal hgk check
$ echo "[extensions]" >> $HGRCPATH
$ echo "hgk=" >> $HGRCPATH
$ hg init repo
$ cd repo
$ echo a > a
$ hg ci -Am adda
adding a
$ hg debug-cat-file commit 0
tree a0c8bcbbb45c
parent 000000000000
author test 0 0
revision 0
branch default
phase draft
adda
$ echo b > b
$ hg ci -Am addb
adding b
$ hg log -T '{node}\n'
102a90ea7b4a3361e4082ed620918c261189a36a
07f4944404050f47db2e5c5071e0e84e7a27bba9
$ hg debug-diff-tree 07f494440405 102a90ea7b4a
:000000 100664 000000000000 1e88685f5dde N b b
$ hg debug-diff-tree 07f494440405 102a90ea7b4a --patch
diff --git a/b b/b
new file mode 100644
--- /dev/null
+++ b/b
@@ -0,0 +1,1 @@
+b
Ensure that diff-tree output isn't affected by diffopts
$ hg --config diff.noprefix=True debug-diff-tree 07f494440405 102a90ea7b4a
:000000 100664 000000000000 1e88685f5dde N b b
$ hg --config diff.noprefix=True debug-diff-tree --patch 07f494440405 102a90ea7b4a
diff --git a/b b/b
new file mode 100644
--- /dev/null
+++ b/b
@@ -0,0 +1,1 @@
+b
$ cd ..