bundle2: avoid unbound read when seeking
Currently, seekableunbundlepart.seek() will perform a read() during
seek operations. This will allocate a buffer to hold the raw data
over the seek distance. This can lead to very large allocations
and cause performance to suffer.
We change the code to perform read(32768) in a loop to avoid
potentially large allocations.
`hg perfbundleread` on an uncompressed Firefox bundle reveals
a performance impact:
! bundle2 iterparts()
! wall 2.992605 comb 2.990000 user 2.260000 sys 0.730000 (best of 4)
! bundle2 iterparts() seekable
! wall 3.863810 comb 3.860000 user 3.000000 sys 0.860000 (best of 3)
! bundle2 part seek()
! wall 6.213387 comb 6.200000 user 3.350000 sys 2.850000 (best of 3)
! wall 3.820347 comb 3.810000 user 2.980000 sys 0.830000 (best of 3)
Since seekable bundle parts are (only) used by bundlerepo, this /may/
speed up initial loading of bundle-based repos. But any improvement
will likely only be noticed on very large bundles.
Differential Revision: https://phab.mercurial-scm.org/D1394
#require bzr
N.B. bzr 1.13 has a bug that breaks this test. If you see this
test fail, check your bzr version. Upgrading to bzr 1.13.1
should fix it.
$ . "$TESTDIR/bzr-definitions"
test multiple merges at once
$ mkdir test-multimerge
$ cd test-multimerge
$ bzr init -q source
$ cd source
$ echo content > file
$ bzr add -q file
$ bzr commit -q -m 'Initial add'
$ cd ..
$ bzr branch -q source source-branch1
$ cd source-branch1
$ echo morecontent >> file
$ echo evenmorecontent > file-branch1
$ bzr add -q file-branch1
$ bzr commit -q -m 'Added branch1 file'
$ cd ../source
$ sleep 1
$ echo content > file-parent
$ bzr add -q file-parent
$ bzr commit -q -m 'Added parent file'
$ cd ..
$ bzr branch -q source source-branch2
$ cd source-branch2
$ echo somecontent > file-branch2
$ bzr add -q file-branch2
$ bzr commit -q -m 'Added brach2 file'
$ sleep 1
$ cd ../source
$ bzr merge -q ../source-branch1
$ bzr merge -q --force ../source-branch2
$ bzr commit -q -m 'Merged branches'
$ cd ..
$ hg convert --datesort source source-hg
initializing destination source-hg repository
scanning source...
sorting...
converting...
4 Initial add
3 Added branch1 file
2 Added parent file
1 Added brach2 file
0 Merged branches
$ glog -R source-hg
o 5@source "(octopus merge fixup)" files:
|\
| o 4@source "Merged branches" files: file-branch2
| |\
o---+ 3@source-branch2 "Added brach2 file" files: file-branch2
/ /
| o 2@source "Added parent file" files: file-parent
| |
o | 1@source-branch1 "Added branch1 file" files: file file-branch1
|/
o 0@source "Initial add" files: file
$ manifest source-hg tip
% manifest of tip
644 file
644 file-branch1
644 file-branch2
644 file-parent
$ cd ..