bundle2: increase payload part chunk size to 32kb
Bundle2 payload parts are framed chunks. Esentially, we obtain
data in equal size chunks of size `preferedchunksize` and emit those
to a generator. That generator is fed into a compressor (which can
be the no-op compressor, which just re-emits the generator). And
the output from the compressor likely goes to a file descriptor
or socket.
What this means is that small chunk sizes create more Python objects
and Python function calls than larger chunk sizes. And as we know,
Python object and function call overhead in performance sensitive
code matters (at least with CPython).
This commit increases the bundle2 part payload chunk size from 4k
to 32k. Practically speaking, this means that the chunks we feed
into a compressor (implemented in C code) or feed directly into a
file handle or socket write() are larger. It's possible the chunks
might be larger than what the receiver can handle in one logical
operation. But at that point, we're in C code, which is much more
efficient at dealing with splitting up the chunk and making multiple
function calls than Python is.
A downside to larger chunks is that the receiver has to wait for that
much data to arrive (either raw or from a decompressor) before it
can process the chunk. But 32kb still feels like a small buffer to
have to wait for. And in many cases, the client will convert from
8 read(4096) to 1 read(32768). That's happening in Python land. So
we cut down on the number of Python objects and function calls,
making the client faster as well. I don't think there are any
significant concerns to increasing the payload chunk size to 32kb.
The impact of this change on performance significant. Using `curl`
to obtain a stream clone bundle2 payload from a server on localhost
serving the mozilla-unified repository:
before: 20.78 user; 7.71 system; 80.5 MB/s
after: 13.90 user; 3.51 system; 132 MB/s
legacy: 9.72 user; 8.16 system; 132 MB/s
bundle2 stream clone generation is still more resource intensive than
legacy stream clone (that's likely because of the use of a
util.chunkbuffer). But the throughput is the same. We might
be in territory we're this is effectively a benchmark of the
networking stack or Python's syscall throughput.
From the client perspective, `hg clone -U --stream`:
before: 33.50 user; 7.95 system; 53.3 MB/s
after: 22.82 user; 7.33 system; 72.7 MB/s
legacy: 29.96 user; 7.94 system; 58.0 MB/s
And for `hg clone --stream` with a working directory update of
~230k files:
after: 119.55 user; 26.47 system; 0:57.08 wall
legacy: 126.98 user; 26.94 system; 1:05.56 wall
So, it appears that bundle2's stream clone is now definitively faster
than legacy stream clone!
Differential Revision: https://phab.mercurial-scm.org/D1932
Journal extension test: tests the share extension support
$ cat >> testmocks.py << EOF
> # mock out util.getuser() and util.makedate() to supply testable values
> import os
> from mercurial import util
> def mockgetuser():
> return 'foobar'
>
> def mockmakedate():
> filename = os.path.join(os.environ['TESTTMP'], 'testtime')
> try:
> with open(filename, 'rb') as timef:
> time = float(timef.read()) + 1
> except IOError:
> time = 0.0
> with open(filename, 'wb') as timef:
> timef.write(str(time))
> return (time, 0)
>
> util.getuser = mockgetuser
> util.makedate = mockmakedate
> EOF
$ cat >> $HGRCPATH << EOF
> [extensions]
> journal=
> share=
> testmocks=`pwd`/testmocks.py
> [remotenames]
> rename.default=remote
> EOF
$ hg init repo
$ cd repo
$ hg bookmark bm
$ touch file0
$ hg commit -Am file0-added
adding file0
$ hg journal --all
previous locations of the working copy and bookmarks:
0fd3805711f9 . commit -Am file0-added
0fd3805711f9 bm commit -Am file0-added
A shared working copy initially receives the same bookmarks and working copy
$ cd ..
$ hg share repo shared1
updating working directory
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd shared1
$ hg journal --all
previous locations of the working copy and bookmarks:
0fd3805711f9 . share repo shared1
unless you explicitly share bookmarks
$ cd ..
$ hg share --bookmarks repo shared2
updating working directory
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd shared2
$ hg journal --all
previous locations of the working copy and bookmarks:
0fd3805711f9 . share --bookmarks repo shared2
0fd3805711f9 bm commit -Am file0-added
Moving the bookmark in the original repository is only shown in the repository
that shares bookmarks
$ cd ../repo
$ touch file1
$ hg commit -Am file1-added
adding file1
$ cd ../shared1
$ hg journal --all
previous locations of the working copy and bookmarks:
0fd3805711f9 . share repo shared1
$ cd ../shared2
$ hg journal --all
previous locations of the working copy and bookmarks:
4f354088b094 bm commit -Am file1-added
0fd3805711f9 . share --bookmarks repo shared2
0fd3805711f9 bm commit -Am file0-added
But working copy changes are always 'local'
$ cd ../repo
$ hg up 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
(leaving bookmark bm)
$ hg journal --all
previous locations of the working copy and bookmarks:
0fd3805711f9 . up 0
4f354088b094 . commit -Am file1-added
4f354088b094 bm commit -Am file1-added
0fd3805711f9 . commit -Am file0-added
0fd3805711f9 bm commit -Am file0-added
$ cd ../shared2
$ hg journal --all
previous locations of the working copy and bookmarks:
4f354088b094 bm commit -Am file1-added
0fd3805711f9 . share --bookmarks repo shared2
0fd3805711f9 bm commit -Am file0-added
$ hg up tip
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg up 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ hg journal
previous locations of '.':
0fd3805711f9 up 0
4f354088b094 up tip
0fd3805711f9 share --bookmarks repo shared2
Unsharing works as expected; the journal remains consistent
$ cd ../shared1
$ hg unshare
$ hg journal --all
previous locations of the working copy and bookmarks:
0fd3805711f9 . share repo shared1
$ cd ../shared2
$ hg unshare
$ hg journal --all
previous locations of the working copy and bookmarks:
0fd3805711f9 . up 0
4f354088b094 . up tip
4f354088b094 bm commit -Am file1-added
0fd3805711f9 . share --bookmarks repo shared2
0fd3805711f9 bm commit -Am file0-added
New journal entries in the source repo no longer show up in the other working copies
$ cd ../repo
$ hg bookmark newbm -r tip
$ hg journal newbm
previous locations of 'newbm':
4f354088b094 bookmark newbm -r tip
$ cd ../shared2
$ hg journal newbm
previous locations of 'newbm':
no recorded locations
This applies for both directions
$ hg bookmark shared2bm -r tip
$ hg journal shared2bm
previous locations of 'shared2bm':
4f354088b094 bookmark shared2bm -r tip
$ cd ../repo
$ hg journal shared2bm
previous locations of 'shared2bm':
no recorded locations