Mercurial > hg
view tests/test-symlinks.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.
author | Gregory Szorc <gregory.szorc@gmail.com> |
---|---|
date | Fri, 09 Oct 2015 11:22:01 -0700 |
parents | 4d2b9b304ad0 |
children | 96ca817ec192 |
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#require symlink == tests added in 0.7 == $ hg init test-symlinks-0.7; cd test-symlinks-0.7; $ touch foo; ln -s foo bar; ln -s nonexistent baz import with add and addremove -- symlink walking should _not_ screwup. $ hg add adding bar adding baz adding foo $ hg forget bar baz foo $ hg addremove adding bar adding baz adding foo commit -- the symlink should _not_ appear added to dir state $ hg commit -m 'initial' $ touch bomb again, symlink should _not_ show up on dir state $ hg addremove adding bomb Assert screamed here before, should go by without consequence $ hg commit -m 'is there a bug?' $ cd .. == fifo & ignore == $ hg init test; cd test; $ mkdir dir $ touch a.c dir/a.o dir/b.o test what happens if we want to trick hg $ hg commit -A -m 0 adding a.c adding dir/a.o adding dir/b.o $ echo "relglob:*.o" > .hgignore $ rm a.c $ rm dir/a.o $ rm dir/b.o $ mkdir dir/a.o $ ln -s nonexistent dir/b.o $ mkfifo a.c it should show a.c, dir/a.o and dir/b.o deleted $ hg status M dir/b.o ! a.c ! dir/a.o ? .hgignore $ hg status a.c a.c: unsupported file type (type is fifo) ! a.c $ cd .. == symlinks from outside the tree == test absolute path through symlink outside repo $ p=`pwd` $ hg init x $ ln -s x y $ cd x $ touch f $ hg add f $ hg status "$p"/y/f A f try symlink outside repo to file inside $ ln -s x/f ../z this should fail $ hg status ../z && { echo hg mistakenly exited with status 0; exit 1; } || : abort: ../z not under root '$TESTTMP/x' $ cd .. == cloning symlinks == $ hg init clone; cd clone; try cloning symlink in a subdir 1. commit a symlink $ mkdir -p a/b/c $ cd a/b/c $ ln -s /path/to/symlink/source demo $ cd ../../.. $ hg stat ? a/b/c/demo $ hg commit -A -m 'add symlink in a/b/c subdir' adding a/b/c/demo 2. clone it $ cd .. $ hg clone clone clonedest updating to branch default 1 files updated, 0 files merged, 0 files removed, 0 files unresolved == symlink and git diffs == git symlink diff $ cd clonedest $ hg diff --git -r null:tip diff --git a/a/b/c/demo b/a/b/c/demo new file mode 120000 --- /dev/null +++ b/a/b/c/demo @@ -0,0 +1,1 @@ +/path/to/symlink/source \ No newline at end of file $ hg export --git tip > ../sl.diff import git symlink diff $ hg rm a/b/c/demo $ hg commit -m'remove link' $ hg import ../sl.diff applying ../sl.diff $ hg diff --git -r 1:tip diff --git a/a/b/c/demo b/a/b/c/demo new file mode 120000 --- /dev/null +++ b/a/b/c/demo @@ -0,0 +1,1 @@ +/path/to/symlink/source \ No newline at end of file == symlinks and addremove == directory moved and symlinked $ mkdir foo $ touch foo/a $ hg ci -Ama adding foo/a $ mv foo bar $ ln -s bar foo $ hg status ! foo/a ? bar/a ? foo now addremove should remove old files $ hg addremove adding bar/a adding foo removing foo/a commit and update back $ hg ci -mb $ hg up '.^' 1 files updated, 0 files merged, 2 files removed, 0 files unresolved $ hg up tip 2 files updated, 0 files merged, 1 files removed, 0 files unresolved $ cd .. == root of repository is symlinked == $ hg init root $ ln -s root link $ cd root $ echo foo > foo $ hg status ? foo $ hg status ../link ? foo $ hg add foo $ hg cp foo "$TESTTMP/link/bar" foo has not been committed yet, so no copy data will be stored for bar. $ cd .. $ hg init b $ cd b $ ln -s nothing dangling $ hg commit -m 'commit symlink without adding' dangling abort: dangling: file not tracked! [255] $ hg add dangling $ hg commit -m 'add symlink' $ hg tip -v changeset: 0:cabd88b706fc tag: tip user: test date: Thu Jan 01 00:00:00 1970 +0000 files: dangling description: add symlink $ hg manifest --debug 2564acbe54bbbedfbf608479340b359f04597f80 644 @ dangling $ readlink.py dangling dangling -> nothing $ rm dangling $ ln -s void dangling $ hg commit -m 'change symlink' $ readlink.py dangling dangling -> void modifying link $ rm dangling $ ln -s empty dangling $ readlink.py dangling dangling -> empty reverting to rev 0: $ hg revert -r 0 -a reverting dangling $ readlink.py dangling dangling -> nothing backups: $ readlink.py *.orig dangling.orig -> empty $ rm *.orig $ hg up -C 1 files updated, 0 files merged, 0 files removed, 0 files unresolved copies $ hg cp -v dangling dangling2 copying dangling to dangling2 $ hg st -Cmard A dangling2 dangling $ readlink.py dangling dangling2 dangling -> void dangling2 -> void Issue995: hg copy -A incorrectly handles symbolic links $ hg up -C 0 files updated, 0 files merged, 0 files removed, 0 files unresolved $ mkdir dir $ ln -s dir dirlink $ hg ci -qAm 'add dirlink' $ mkdir newdir $ mv dir newdir/dir $ mv dirlink newdir/dirlink $ hg mv -A dirlink newdir/dirlink $ cd ..