tests/test-debugcommands.t

revlog: add config variable for limiting delta-chain length

The current heuristic for deciding between storing delta and full texts
is based on ratio of (sizeofdeltas)/(sizeoffulltext).

In some cases (for example a manifest for ahuge repo) this approach
can result in extremely long delta chains (~30,000) which are very slow to
read. (In the case of a manifest ~500ms are added to every hg command because of that).

This commit introduces "revlog.maxchainlength" configuration variable that will
limit delta chain length.

  $ hg init debugrevlog
  $ cd debugrevlog
  $ echo a > a
  $ hg ci -Am adda
  adding a
  $ hg debugrevlog -m
  format : 1
  flags  : inline
  
  revisions     :  1
      merges    :  0 ( 0.00%)
      normal    :  1 (100.00%)
  revisions     :  1
      full      :  1 (100.00%)
      deltas    :  0 ( 0.00%)
  revision size : 44
      full      : 44 (100.00%)
      deltas    :  0 ( 0.00%)
  
  avg chain length  : 0
  compression ratio : 0
  
  uncompressed data size (min/max/avg) : 43 / 43 / 43
  full revision size (min/max/avg)     : 44 / 44 / 44
  delta size (min/max/avg)             : 0 / 0 / 0

Test max chain len
  $ cat >> $HGRCPATH << EOF
  > [revlog]
  > maxchainlen=4
  > EOF

  $ echo "This test checks if maxchainlen config value is respected also it can serve as basic test for debugrevlog -d <file>.\n" >> a
  $ hg ci -m a
  $ echo "b\n" >> a
  $ hg ci -m a
  $ echo "c\n" >> a
  $ hg ci -m a
  $ echo "d\n" >> a
  $ hg ci -m a
  $ echo "e\n" >> a
  $ hg ci -m a
  $ echo "f\n" >> a
  $ hg ci -m a
  $ echo 'g\n' >> a
  $ hg ci -m a
  $ echo 'h\n' >> a
  $ hg ci -m a
  $ hg debugrevlog -d a
  # rev p1rev p2rev start   end deltastart base   p1   p2 rawsize totalsize compression heads chainlen
      0    -1    -1     0   ???          0    0    0    0     ???      ????           ?     1        0 (glob)
      1     0    -1   ???   ???          0    0    0    0     ???      ????           ?     1        1 (glob)
      2     1    -1   ???   ???        ???  ???  ???    0     ???      ????           ?     1        2 (glob)
      3     2    -1   ???   ???        ???  ???  ???    0     ???      ????           ?     1        3 (glob)
      4     3    -1   ???   ???        ???  ???  ???    0     ???      ????           ?     1        4 (glob)
      5     4    -1   ???   ???        ???  ???  ???    0     ???      ????           ?     1        0 (glob)
      6     5    -1   ???   ???        ???  ???  ???    0     ???      ????           ?     1        1 (glob)
      7     6    -1   ???   ???        ???  ???  ???    0     ???      ????           ?     1        2 (glob)
      8     7    -1   ???   ???        ???  ???  ???    0     ???      ????           ?     1        3 (glob)
  $ cd ..

Test internal debugstacktrace command

  $ cat > debugstacktrace.py << EOF
  > from mercurial.util import debugstacktrace, dst, sys
  > def f():
  >     dst('hello world')
  > def g():
  >     f()
  >     debugstacktrace(skip=-5, f=sys.stdout)
  > g()
  > EOF
  $ python debugstacktrace.py
  hello world at:
   debugstacktrace.py:7 in * (glob)
   debugstacktrace.py:5 in g
   debugstacktrace.py:3 in f
  stacktrace at:
   debugstacktrace.py:7 *in * (glob)
   debugstacktrace.py:6 *in g (glob)
   */util.py:* in debugstacktrace (glob)