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
$ hg init
$ echo a > a
$ hg ci -qAm 'add a'
$ hg init subrepo
$ echo 'subrepo = http://example.net/libfoo' > .hgsub
$ hg ci -qAm 'added subrepo'
$ hg up -qC 0
$ echo ax > a
$ hg ci -m 'changed a'
created new head
$ hg up -qC 1
$ cd subrepo
$ echo b > b
$ hg add b
$ cd ..
Should fail, since there are added files to subrepo:
$ hg merge
abort: uncommitted changes in subrepository "subrepo"
[255]
Deleted files trigger a '+' marker in top level repos. Deleted files are also
noticed by `update --check` in the top level repo.
$ hg ci -Sqm 'add b'
$ echo change > subrepo/b
$ hg ci -Sm 'change b'
committing subrepository subrepo
$ rm a
$ hg id
9bfe45a197d7+ tip
$ hg sum
parent: 4:9bfe45a197d7 tip
change b
branch: default
commit: 1 deleted (clean)
update: 1 new changesets, 2 branch heads (merge)
phases: 5 draft
$ hg up --check -r '.^'
abort: uncommitted changes
[255]
$ hg st -S
! a
$ hg up -Cq .
Test that dirty is consistent through subrepos
$ rm subrepo/b
A deleted subrepo file is flagged as dirty, like the top level repo
$ hg id --config extensions.blackbox= --config blackbox.dirty=True
9bfe45a197d7+ tip
$ cat .hg/blackbox.log
* @9bfe45a197d7b0ab09bf287729dd57e9619c9da5+ (*)> serve --cmdserver chgunix * (glob) (chg !)
* @9bfe45a197d7b0ab09bf287729dd57e9619c9da5+ (*)> id --config *extensions.blackbox=* --config *blackbox.dirty=True* (glob)
* @9bfe45a197d7b0ab09bf287729dd57e9619c9da5+ (*)> id --config *extensions.blackbox=* --config *blackbox.dirty=True* exited 0 * (glob)
TODO: a deleted file should be listed as such, like the top level repo
$ hg sum
parent: 4:9bfe45a197d7 tip
change b
branch: default
commit: (clean)
update: 1 new changesets, 2 branch heads (merge)
phases: 5 draft
Modified subrepo files are noticed by `update --check` and `summary`
$ echo mod > subrepo/b
$ hg st -S
M subrepo/b
$ hg up -r '.^' --check
abort: uncommitted changes in subrepository "subrepo"
[255]
$ hg sum
parent: 4:9bfe45a197d7 tip
change b
branch: default
commit: 1 subrepos
update: 1 new changesets, 2 branch heads (merge)
phases: 5 draft
TODO: why is -R needed here? If it's because the subrepo is treated as a
discrete unit, then this should probably warn or something.
$ hg revert -R subrepo --no-backup subrepo/b -r .
$ rm subrepo/b
$ hg st -S
! subrepo/b
`hg update --check` notices a subrepo with a missing file, like it notices a
missing file in the top level repo.
$ hg up -r '.^' --check
abort: uncommitted changes in subrepository "subrepo"
[255]
$ hg up -r '.^' --config ui.interactive=True << EOF
> d
> EOF
other [destination] changed b which local [working copy] deleted
use (c)hanged version, leave (d)eleted, or leave (u)nresolved? d
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
XXX: There's a difference between wdir() and '.', so there should be a status.
`hg files -S` from the top is also missing 'subrepo/b'.
$ hg st -S
$ hg st -R subrepo
$ hg files -R subrepo
[1]
$ hg files -R subrepo -r '.'
subrepo/b
$ hg bookmark -r tip @other
$ echo xyz > subrepo/c
$ hg ci -SAm 'add c'
adding subrepo/c
committing subrepository subrepo
created new head
$ rm subrepo/c
Merge sees deleted subrepo files as an uncommitted change
$ hg merge @other
abort: uncommitted changes in subrepository "subrepo"
[255]