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
$ hg init
$ echo foo > a
$ hg add a
$ hg commit -m "1"
$ echo bar > b
$ hg add b
$ hg remove a
Should show a removed and b added:
$ hg status
A b
R a
$ hg revert --all
undeleting a
forgetting b
Should show b unknown and a back to normal:
$ hg status
? b
$ rm b
$ hg co -C 0
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo foo-a > a
$ hg commit -m "2a"
$ hg co -C 0
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo foo-b > a
$ hg commit -m "2b"
created new head
$ HGMERGE=true hg merge 1
merging a
0 files updated, 1 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
Should show foo-b:
$ cat a
foo-b
$ echo bar > b
$ hg add b
$ rm a
$ hg remove a
Should show a removed and b added:
$ hg status
A b
R a
Revert should fail:
$ hg revert
abort: uncommitted merge with no revision specified
(use 'hg update' or see 'hg help revert')
[255]
Revert should be ok now:
$ hg revert -r2 --all
undeleting a
forgetting b
Should show b unknown and a marked modified (merged):
$ hg status
M a
? b
Should show foo-b:
$ cat a
foo-b