view tests/test-convert-svn-source.t @ 26623:5a95fe44121d

clonebundles: support for seeding clones from pre-generated bundles

Cloning can be an expensive operation for servers because the server
generates a bundle from existing repository data at request time. For
a large repository like mozilla-central, this consumes 4+ minutes
of CPU time on the server. It also results in significant network
utilization. Multiplied by hundreds or even thousands of clients and
the ensuing load can result in difficulties scaling the Mercurial server.

Despite generation of bundles being deterministic until the next
changeset is added, the generation of bundles to service a clone request
is not cached. Each clone thus performs redundant work. This is
wasteful.

This patch introduces the "clonebundles" extension and related
client-side functionality to help alleviate this deficiency. The
client-side feature is behind an experimental flag and is not enabled by
default.

It works as follows:

1) Server operator generates a bundle and makes it available on a
   server (likely HTTP).
2) Server operator defines the URL of a bundle file in a
   .hg/clonebundles.manifest file.
3) Client `hg clone`ing sees the server is advertising bundle URLs.
4) Client fetches and applies the advertised bundle.
5) Client performs equivalent of `hg pull` to fetch changes made since
   the bundle was created.

Essentially, the server performs the expensive work of generating a
bundle once and all subsequent clones fetch a static file from
somewhere. Scaling static file serving is a much more manageable
problem than scaling a Python application like Mercurial. Assuming your
repository grows less than 1% per day, the end result is 99+% of CPU
and network load from clones is eliminated, allowing Mercurial servers
to scale more easily. Serving static files also means data can be
transferred to clients as fast as they can consume it, rather than as
fast as servers can generate it. This makes clones faster.

Mozilla has implemented similar functionality of this patch on
hg.mozilla.org using a custom extension. We are hosting bundle files in
Amazon S3 and CloudFront (a CDN) and have successfully offloaded
>1 TB/day in data transfer from hg.mozilla.org, freeing up significant
bandwidth and CPU resources. The positive impact has been stellar and
I believe it has proved its value to be included in Mercurial core. I
feel it is important for the client-side support to be enabled in core
by default because it means that clients will get faster, more reliable
clones and will enable server operators to reduce load without
requiring any client-side configuration changes (assuming clients are
up to date, of course).

The scope of this feature is narrowly and specifically tailored to
cloning, despite "serve pulls from pre-generated bundles" being a valid
and useful feature. I would eventually like for Mercurial servers to
support transferring *all* repository data via statically hosted files.
You could imagine a server that siphons all pushed data to bundle files
and instructs clients to apply a stream of bundles to reconstruct all
repository data. This feature, while useful and powerful, is
significantly more work to implement because it requires the server
component have awareness of discovery and a mapping of which changesets
are in which files. Full, clone bundles, by contrast, are much simpler.

The wire protocol command is named "clonebundles" instead of something
more generic like "staticbundles" to leave the door open for a new, more
powerful and more generic server-side component with minimal backwards
compatibility implications. The name "bundleclone" is used by Mozilla's
extension and would cause problems since there are subtle differences
in Mozilla's extension.

Mozilla's experience with this idea has taught us that some form of
"content negotiation" is required. Not all clients will support all
bundle formats or even URLs (advanced TLS requirements, etc). To ensure
the highest uptake possible, a server needs to advertise multiple
versions of bundles and clients need to be able to choose the most
appropriate from that list one. The "attributes" in each
server-advertised entry facilitate this filtering and sorting. Their
use will become apparent in subsequent patches.

Initial inspiration and credit for the idea of cloning from static files
belongs to Augie Fackler and his "lookaside clone" extension proof of
concept.

#require svn svn-bindings

  $ cat >> $HGRCPATH <<EOF
  > [extensions]
  > convert =
  > [convert]
  > svn.trunk = mytrunk
  > EOF

  $ svnadmin create svn-repo
  $ SVNREPOPATH=`pwd`/svn-repo
#if windows
  $ SVNREPOURL=file:///`$PYTHON -c "import urllib, sys; sys.stdout.write(urllib.quote(sys.argv[1]))" "$SVNREPOPATH"`
#else
  $ SVNREPOURL=file://`$PYTHON -c "import urllib, sys; sys.stdout.write(urllib.quote(sys.argv[1]))" "$SVNREPOPATH"`
#endif
  $ INVALIDREVISIONID=svn:x2147622-4a9f-4db4-a8d3-13562ff547b2/proj%20B/mytrunk@1
  $ VALIDREVISIONID=svn:a2147622-4a9f-4db4-a8d3-13562ff547b2/proj%20B/mytrunk/mytrunk@1

Now test that it works with trunk/tags layout, but no branches yet.

Initial svn import

  $ mkdir projB
  $ cd projB
  $ mkdir mytrunk
  $ mkdir tags
  $ cd ..

  $ svn import -m "init projB" projB "$SVNREPOURL/proj%20B" | sort
  
  Adding         projB/mytrunk (glob)
  Adding         projB/tags (glob)
  Committed revision 1.

Update svn repository

  $ svn co "$SVNREPOURL/proj%20B/mytrunk" B
  Checked out revision 1.
  $ cd B
  $ echo hello > 'letter .txt'
  $ svn add 'letter .txt'
  A         letter .txt
  $ svn ci -m hello
  Adding         letter .txt
  Transmitting file data .
  Committed revision 2.

  $ svn-safe-append.py world 'letter .txt'
  $ svn ci -m world
  Sending        letter .txt
  Transmitting file data .
  Committed revision 3.

  $ svn copy -m "tag v0.1" "$SVNREPOURL/proj%20B/mytrunk" "$SVNREPOURL/proj%20B/tags/v0.1"
  
  Committed revision 4.

  $ svn-safe-append.py 'nice day today!' 'letter .txt'
  $ svn ci -m "nice day"
  Sending        letter .txt
  Transmitting file data .
  Committed revision 5.
  $ cd ..

Convert to hg once and also test localtimezone option

NOTE: This doesn't check all time zones -- it merely determines that
the configuration option is taking effect.

An arbitrary (U.S.) time zone is used here.  TZ=US/Hawaii is selected
since it does not use DST (unlike other U.S. time zones) and is always
a fixed difference from UTC.

  $ TZ=US/Hawaii hg convert --config convert.localtimezone=True "$SVNREPOURL/proj%20B" B-hg
  initializing destination B-hg repository
  scanning source...
  sorting...
  converting...
  3 init projB
  2 hello
  1 world
  0 nice day
  updating tags

Update svn repository again

  $ cd B
  $ svn-safe-append.py "see second letter" 'letter .txt'
  $ echo "nice to meet you" > letter2.txt
  $ svn add letter2.txt
  A         letter2.txt
  $ svn ci -m "second letter"
  Sending        letter .txt
  Adding         letter2.txt
  Transmitting file data ..
  Committed revision 6.

  $ svn copy -m "tag v0.2" "$SVNREPOURL/proj%20B/mytrunk" "$SVNREPOURL/proj%20B/tags/v0.2"
  
  Committed revision 7.

  $ svn-safe-append.py "blah-blah-blah" letter2.txt
  $ svn ci -m "work in progress"
  Sending        letter2.txt
  Transmitting file data .
  Committed revision 8.
  $ cd ..

  $ hg convert -s svn "$SVNREPOURL/proj%20B/non-existent-path" dest
  initializing destination dest repository
  abort: no revision found in module /proj B/non-existent-path
  [255]

########################################

Test incremental conversion

  $ TZ=US/Hawaii hg convert --config convert.localtimezone=True "$SVNREPOURL/proj%20B" B-hg
  scanning source...
  sorting...
  converting...
  1 second letter
  0 work in progress
  updating tags

  $ cd B-hg
  $ hg log -G --template '{rev} {desc|firstline} date: {date|date} files: {files}\n'
  o  7 update tags date: * +0000 files: .hgtags (glob)
  |
  o  6 work in progress date: * -1000 files: letter2.txt (glob)
  |
  o  5 second letter date: * -1000 files: letter .txt letter2.txt (glob)
  |
  o  4 update tags date: * +0000 files: .hgtags (glob)
  |
  o  3 nice day date: * -1000 files: letter .txt (glob)
  |
  o  2 world date: * -1000 files: letter .txt (glob)
  |
  o  1 hello date: * -1000 files: letter .txt (glob)
  |
  o  0 init projB date: * -1000 files: (glob)
  
  $ hg tags -q
  tip
  v0.2
  v0.1
  $ cd ..

Test filemap
  $ echo 'include letter2.txt' > filemap
  $ hg convert --filemap filemap "$SVNREPOURL/proj%20B/mytrunk" fmap
  initializing destination fmap repository
  scanning source...
  sorting...
  converting...
  5 init projB
  4 hello
  3 world
  2 nice day
  1 second letter
  0 work in progress
  $ hg -R fmap branch -q
  default
  $ hg log -G -R fmap --template '{rev} {desc|firstline} files: {files}\n'
  o  1 work in progress files: letter2.txt
  |
  o  0 second letter files: letter2.txt
  
Convert with --full adds and removes files that didn't change

  $ cd B
  $ echo >> "letter .txt"
  $ svn ci -m 'nothing'
  Sending        letter .txt
  Transmitting file data .
  Committed revision 9.
  $ cd ..

  $ echo 'rename letter2.txt letter3.txt' > filemap
  $ hg convert --filemap filemap --full "$SVNREPOURL/proj%20B/mytrunk" fmap
  scanning source...
  sorting...
  converting...
  0 nothing
  $ hg -R fmap st --change tip
  A letter .txt
  A letter3.txt
  R letter2.txt

test invalid splicemap1

  $ cat > splicemap <<EOF
  > $INVALIDREVISIONID $VALIDREVISIONID
  > EOF
  $ hg convert --splicemap splicemap "$SVNREPOURL/proj%20B/mytrunk" smap
  initializing destination smap repository
  abort: splicemap entry svn:x2147622-4a9f-4db4-a8d3-13562ff547b2/proj%20B/mytrunk@1 is not a valid revision identifier
  [255]

Test stop revision
  $ hg convert --rev 1 "$SVNREPOURL/proj%20B/mytrunk" stoprev
  initializing destination stoprev repository
  scanning source...
  sorting...
  converting...
  0 init projB
  $ hg -R stoprev branch -q
  default

Check convert_revision extra-records.
This is also the only place testing more than one extra field in a revision.

  $ cd stoprev
  $ hg tip --debug | grep extra
  extra:       branch=default
  extra:       convert_revision=svn:........-....-....-....-............/proj B/mytrunk@1 (re)
  $ cd ..

Test converting empty heads (issue3347).
Also tests getting logs directly without debugsvnlog.

  $ svnadmin create svn-empty
  $ svnadmin load -q svn-empty < "$TESTDIR/svn/empty.svndump"
  $ hg --config convert.svn.trunk= --config convert.svn.debugsvnlog=0 convert svn-empty
  assuming destination svn-empty-hg
  initializing destination svn-empty-hg repository
  scanning source...
  sorting...
  converting...
  1 init projA
  0 adddir
  $ hg --config convert.svn.trunk= convert "$SVNREPOURL/../svn-empty/trunk"
  assuming destination trunk-hg
  initializing destination trunk-hg repository
  scanning source...
  sorting...
  converting...
  1 init projA
  0 adddir

Test that a too-new repository format is properly rejected:
  $ mv svn-empty/format format
  $ echo 999 > svn-empty/format
It's important that this command explicitly specify svn, otherwise it
can have surprising side effects (like falling back to a perforce
depot that can be seen from the test environment and slurping from that.)
  $ hg convert --source-type svn svn-empty this-will-fail
  initializing destination this-will-fail repository
  file:/*/$TESTTMP/svn-empty does not look like a Subversion repository to libsvn version 1.*.* (glob)
  abort: svn-empty: missing or unsupported repository
  [255]
  $ mv format svn-empty/format