view tests/test-filebranch.t @ 35793:4fb2bb61597c

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

This test makes sure that we don't mark a file as merged with its ancestor
when we do a merge.

  $ cat <<EOF > merge
  > from __future__ import print_function
  > import sys, os
  > print("merging for", os.path.basename(sys.argv[1]))
  > EOF
  $ HGMERGE="$PYTHON ../merge"; export HGMERGE

Creating base:

  $ hg init a
  $ cd a
  $ echo 1 > foo
  $ echo 1 > bar
  $ echo 1 > baz
  $ echo 1 > quux
  $ hg add foo bar baz quux
  $ hg commit -m "base"

  $ cd ..
  $ hg clone a b
  updating to branch default
  4 files updated, 0 files merged, 0 files removed, 0 files unresolved

Creating branch a:

  $ cd a
  $ echo 2a > foo
  $ echo 2a > bar
  $ hg commit -m "branch a"

Creating branch b:

  $ cd ..
  $ cd b
  $ echo 2b > foo
  $ echo 2b > baz
  $ hg commit -m "branch b"

We shouldn't have anything but n state here:

  $ hg debugstate --nodates | grep -v "^n"
  [1]

Merging:

  $ hg pull ../a
  pulling from ../a
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 2 changes to 2 files (+1 heads)
  new changesets bdd988058d16
  (run 'hg heads' to see heads, 'hg merge' to merge)

  $ hg merge -v
  resolving manifests
  getting bar
  merging foo
  merging for foo
  1 files updated, 1 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ echo 2m > foo
  $ echo 2b > baz
  $ echo new > quux

  $ hg ci -m "merge"

main: we should have a merge here:

  $ hg debugindex --changelog
     rev    offset  length  ..... linkrev nodeid       p1           p2 (re)
       0         0      73  .....       0 cdca01651b96 000000000000 000000000000 (re)
       1        73      68  .....       1 f6718a9cb7f3 cdca01651b96 000000000000 (re)
       2       141      68  .....       2 bdd988058d16 cdca01651b96 000000000000 (re)
       3       209      66  .....       3 d8a521142a3c f6718a9cb7f3 bdd988058d16 (re)

log should show foo and quux changed:

  $ hg log -v -r tip
  changeset:   3:d8a521142a3c
  tag:         tip
  parent:      1:f6718a9cb7f3
  parent:      2:bdd988058d16
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files:       foo quux
  description:
  merge
  
  

foo: we should have a merge here:

  $ hg debugindex foo
     rev    offset  length  ..... linkrev nodeid       p1           p2 (re)
       0         0       3  .....       0 b8e02f643373 000000000000 000000000000 (re)
       1         3       4  .....       1 2ffeddde1b65 b8e02f643373 000000000000 (re)
       2         7       4  .....       2 33d1fb69067a b8e02f643373 000000000000 (re)
       3        11       4  .....       3 aa27919ee430 2ffeddde1b65 33d1fb69067a (re)

bar: we should not have a merge here:

  $ hg debugindex bar
     rev    offset  length  ..... linkrev nodeid       p1           p2 (re)
       0         0       3  .....       0 b8e02f643373 000000000000 000000000000 (re)
       1         3       4  .....       2 33d1fb69067a b8e02f643373 000000000000 (re)

baz: we should not have a merge here:

  $ hg debugindex baz
     rev    offset  length  ..... linkrev nodeid       p1           p2 (re)
       0         0       3  .....       0 b8e02f643373 000000000000 000000000000 (re)
       1         3       4  .....       1 2ffeddde1b65 b8e02f643373 000000000000 (re)

quux: we should not have a merge here:

  $ hg debugindex quux
     rev    offset  length  ..... linkrev nodeid       p1           p2 (re)
       0         0       3  .....       0 b8e02f643373 000000000000 000000000000 (re)
       1         3       5  .....       3 6128c0f33108 b8e02f643373 000000000000 (re)

Manifest entries should match tips of all files:

  $ hg manifest --debug
  33d1fb69067a0139622a3fa3b7ba1cdb1367972e 644   bar
  2ffeddde1b65b4827f6746174a145474129fa2ce 644   baz
  aa27919ee4303cfd575e1fb932dd64d75aa08be4 644   foo
  6128c0f33108e8cfbb4e0824d13ae48b466d7280 644   quux

Everything should be clean now:

  $ hg status

  $ hg verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  4 files, 4 changesets, 10 total revisions

  $ cd ..