tests/test-pull-r.t

revlog: don't flush data file after every added revision

The current behavior of revlogs is to flush the data file when writing
data to it. Tracing system calls revealed that changegroup processing
incurred numerous write(2) calls for values much smaller than the
default buffer size (Python defaults to 4096, but it can be adjusted
based on detected block size at run time by CPython).

The reason we flush revlogs is so readers have all data available.
For example, the current code in revlog.py will re-open the revlog
file (instead of seeking an existing file handle) to read the text
of a revision. This happens when starting a new delta chain when
adding several revisions from changegroups, for example. Yes, this
is likely sub-optimal (we should probably be sharing file descriptors
between readers and writers to avoid the flushing and associated
overhead of re-opening files).

While flushing revlogs is necessary, it appears all callers are
diligent about flushing files before a read is performed (see
buildtext() in _addrevision()), making the flush in
_writeentry() redundant and unncessary. So, we remove it. In practice,
this means we incur a write(2) a) when the buffer is full (typically
4096 bytes) b) when a new delta chain is created rather than after
every added revision. This applies to every revlog, but by volume
it mostly impacts filelogs.

Removing the redundant flush from _writeentry() significantly
reduces the number of write(2) calls during changegroup processing on
my Linux machine. When applying a changegroup of the hg repo based on
my local repo, the total number of write(2) calls during application
of the mercurial/localrepo.py revlogs dropped from 1,320 to 217 with
this patch applied. Total I/O related system calls dropped from 1,577
to 474.

When unbundling a mozilla-central gzipped bundle (264,403 changesets
with 1,492,215 changes to 222,507 files), total write(2) calls
dropped from 1,252,881 to 827,106 and total system calls dropped from
3,601,259 to 3,178,636 - a reduction of 425,775!

While the system call reduction is significant, it appears
to have no impact on wall time on my Linux and Windows machines. Still,
fewer syscalls is fewer syscalls. Surely this can't hurt. If nothing
else, it makes examining remaining system call usage simpler and opens
the door to experimenting with the performance impact of different
buffer sizes.

  $ hg init repo
  $ cd repo
  $ echo foo > foo
  $ hg ci -qAm 'add foo'
  $ echo >> foo
  $ hg ci -m 'change foo'
  $ hg up -qC 0
  $ echo bar > bar
  $ hg ci -qAm 'add bar'

  $ hg log
  changeset:   2:effea6de0384
  tag:         tip
  parent:      0:bbd179dfa0a7
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     add bar
  
  changeset:   1:ed1b79f46b9a
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     change foo
  
  changeset:   0:bbd179dfa0a7
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     add foo
  
  $ cd ..

don't show "(+1 heads)" message when pulling closed head

  $ hg clone -q repo repo2
  $ hg clone -q repo2 repo3
  $ cd repo2
  $ hg up -q 0
  $ echo hello >> foo
  $ hg ci -mx1
  created new head
  $ hg ci -mx2 --close-branch
  $ cd ../repo3
  $ hg heads -q --closed
  2:effea6de0384
  1:ed1b79f46b9a
  $ hg pull
  pulling from $TESTTMP/repo2 (glob)
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 2 changesets with 1 changes to 1 files
  (run 'hg update' to get a working copy)
  $ hg heads -q --closed
  4:00cfe9073916
  2:effea6de0384
  1:ed1b79f46b9a

  $ cd ..

  $ hg init copy
  $ cd copy

Pull a missing revision:

  $ hg pull -qr missing ../repo
  abort: unknown revision 'missing'!
  [255]

Pull multiple revisions with update:

  $ hg pull -qu -r 0 -r 1 ../repo
  $ hg -q parents
  0:bbd179dfa0a7
  $ hg rollback
  repository tip rolled back to revision -1 (undo pull)
  working directory now based on revision -1

  $ hg pull -qr 0 ../repo
  $ hg log
  changeset:   0:bbd179dfa0a7
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     add foo
  
  $ hg pull -qr 1 ../repo
  $ hg log
  changeset:   1:ed1b79f46b9a
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     change foo
  
  changeset:   0:bbd179dfa0a7
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     add foo
  

This used to abort: received changelog group is empty:

  $ hg pull -qr 1 ../repo

Test race condition with -r and -U (issue4707)

We pull '-U -r <name>' and the name change right after/during the changegroup emission.
We use http because http is better is our racy-est option.


  $ echo babar > ../repo/jungle
  $ cat <<EOF > ../repo/.hg/hgrc
  > [hooks]
  > outgoing.makecommit = hg ci -Am 'racy commit'; echo committed in pull-race
  > EOF
  $ hg -R ../repo serve -p $HGPORT2 -d --pid-file=../repo.pid
  $ cat ../repo.pid >> $DAEMON_PIDS
  $ hg pull --rev default --update http://localhost:$HGPORT2/
  pulling from http://localhost:$HGPORT2/
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files (+1 heads)
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg log -G
  @  changeset:   2:effea6de0384
  |  tag:         tip
  |  parent:      0:bbd179dfa0a7
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     add bar
  |
  | o  changeset:   1:ed1b79f46b9a
  |/   user:        test
  |    date:        Thu Jan 01 00:00:00 1970 +0000
  |    summary:     change foo
  |
  o  changeset:   0:bbd179dfa0a7
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     add foo
  

  $ cd ..