view tests/test-clone-cgi.t @ 33207:895ecec31c70

revlog: add an experimental option to mitigated delta issues (issue5480)

The general delta heuristic to select a delta do not scale with the number of
branch. The delta base is frequently too far away to be able to reuse a chain
according to the "distance" criteria. This leads to insertion of larger delta (or
even full text) that themselves push the bases for the next delta further away
leading to more large deltas and full texts. This full text and frequent
recomputation throw Mercurial performance in disarray.

For example of a slightly large repository

  280 000 files (2 150 000 versions)
  430 000 changesets (10 000 topological heads)

Number below compares repository with and without the distance criteria:

manifest size:
    with:    21.4 GB
    without:  0.3 GB

store size:
    with:    28.7 GB
    without   7.4 GB

bundle last 15 00 revisions:
    with:    800 seconds
             971 MB
    without:  50 seconds
              73 MB

unbundle time (of the last 15K revisions):
    with:    1150 seconds (~19 minutes)
    without:   35 seconds

Similar issues has been observed in other repositories.


Adding a new option or "feature" on stable is uncommon. However, given that this
issues is making Mercurial practically unusable, I'm exceptionally targeting
this patch for stable.

What is actually needed is a full rework of the delta building and reading
logic. However, that will be a longer process and churn not suitable for stable.

In the meantime, we introduces a quick and dirty mitigation of this in the
'experimental' config space. The new option introduces a way to set the maximum
amount of memory usable to store a diff in memory. This extend the ability for
Mercurial to create chains without removing all safe guard regarding memory
access. The option should be phased out when core has a more proper solution
available.

Setting the limit to '0' remove all limits, setting it to '-1' use the default
limit (textsize x 4).

#require no-msys # MSYS will translate web paths as if they were file paths

This is a test of the wire protocol over CGI-based hgweb.
initialize repository

  $ hg init test
  $ cd test
  $ echo a > a
  $ hg ci -Ama
  adding a
  $ cd ..
  $ cat >hgweb.cgi <<HGWEB
  > #
  > # An example CGI script to use hgweb, edit as necessary
  > import cgitb
  > cgitb.enable()
  > from mercurial import demandimport; demandimport.enable()
  > from mercurial.hgweb import hgweb
  > from mercurial.hgweb import wsgicgi
  > application = hgweb("test", "Empty test repository")
  > wsgicgi.launch(application)
  > HGWEB
  $ chmod 755 hgweb.cgi

try hgweb request

  $ . "$TESTDIR/cgienv"
  $ QUERY_STRING="cmd=changegroup&roots=0000000000000000000000000000000000000000"; export QUERY_STRING
  $ python hgweb.cgi >page1 2>&1
  $ $PYTHON "$TESTDIR/md5sum.py" page1
  1f424bb22ec05c3c6bc866b6e67efe43  page1

make sure headers are sent even when there is no body

  $ QUERY_STRING="cmd=listkeys&namespace=nosuchnamespace" python hgweb.cgi
  Status: 200 Script output follows\r (esc)
  Content-Type: application/mercurial-0.1\r (esc)
  Content-Length: 0\r (esc)
  \r (esc)