Mercurial > hg
view tests/test-static-http.t @ 40021:c537144fdbef
wireprotov2: support response caching
One of the things I've learned from managing VCS servers over the
years is that they are hard to scale. It is well known that some
companies have very beefy (read: very expensive) servers to power
their VCS needs. It is also known that specialized servers for
various VCS exist in order to facilitate scaling servers. (Mercurial
is in this boat.)
One of the aspects that make a VCS server hard to scale is the
high CPU load incurred by constant client clone/pull operations.
To alleviate the scaling pain associated with data retrieval
operations, I want to integrate caching into the Mercurial wire
protocol server as robustly as possible such that servers can
aggressively cache responses and defer as much server load as
possible.
This commit represents the initial implementation of a general
caching layer in wire protocol version 2.
We define a new interface and behavior for a wire protocol cacher
in repository.py. (This is probably where a reviewer should look
first to understand what is going on.)
The bulk of the added code is in wireprotov2server.py, where we
define how a command can opt in to being cached and integrate
caching into command dispatching.
From a very high-level:
* A command can declare itself as cacheable by providing a callable
that can be used to derive a cache key.
* At dispatch time, if a command is cacheable, we attempt to
construct a cacher and use it for serving the request and/or
caching the request.
* The dispatch layer handles the bulk of the business logic for
caching, making cachers mostly "dumb content stores."
* The mechanism for invalidating cached entries (one of the harder
parts about caching in general) is by varying the cache key when
state changes. As such, cachers don't need to be concerned with
cache invalidation.
Initially, we've hooked up support for caching "manifestdata" and
"filedata" commands. These are the simplest to cache, as they should
be immutable over time. Caching of commands related to changeset
data is a bit harder (because cache validation is impacted by
changes to bookmarks, phases, etc). This will be implemented later.
(Strictly speaking, censoring a file should invalidate caches. I've
added an inline TODO to track this edge case.)
To prove it works, this commit implements a test-only extension
providing in-memory caching backed by an lrucachedict. A new test
showing this extension behaving properly is added. FWIW, the
cacher is ~50 lines of code, demonstrating the relative ease with
which a cache can be added to a server.
While the test cacher is not suitable for production workloads, just
for kicks I performed a clone of just the changeset and manifest data
for the mozilla-unified repository. With a fully warmed cache (of just
the manifest data since changeset data is not cached), server-side
CPU usage dropped from ~73s to ~28s. That's pretty significant and
demonstrates the potential that response caching has on server
scalability!
Differential Revision: https://phab.mercurial-scm.org/D4773
author | Gregory Szorc <gregory.szorc@gmail.com> |
---|---|
date | Wed, 26 Sep 2018 17:16:56 -0700 |
parents | 5abc47d4ca6b |
children | d5357238eda9 |
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#require no-reposimplestore $ hg clone http://localhost:$HGPORT/ copy abort: * (glob) [255] $ test -d copy [1] This server doesn't do range requests so it's basically only good for one pull $ "$PYTHON" "$TESTDIR/dumbhttp.py" -p $HGPORT --pid dumb.pid \ > --logfile server.log $ cat dumb.pid >> $DAEMON_PIDS $ hg init remote $ cd remote $ echo foo > bar $ echo c2 > '.dotfile with spaces' $ hg add adding .dotfile with spaces adding bar $ hg commit -m"test" $ hg tip changeset: 0:02770d679fb8 tag: tip user: test date: Thu Jan 01 00:00:00 1970 +0000 summary: test $ cd .. $ hg clone static-http://localhost:$HGPORT/remote local requesting all changes adding changesets adding manifests adding file changes added 1 changesets with 2 changes to 2 files new changesets 02770d679fb8 updating to branch default 2 files updated, 0 files merged, 0 files removed, 0 files unresolved $ cd local $ hg verify checking changesets checking manifests crosschecking files in changesets and manifests checking files checked 1 changesets with 2 changes to 2 files $ cat bar foo $ cd ../remote $ echo baz > quux $ hg commit -A -mtest2 adding quux check for HTTP opener failures when cachefile does not exist $ rm .hg/cache/* $ cd ../local $ cat >> .hg/hgrc <<EOF > [hooks] > changegroup = sh -c "printenv.py changegroup" > EOF $ hg pull pulling from static-http://localhost:$HGPORT/remote searching for changes adding changesets adding manifests adding file changes added 1 changesets with 1 changes to 1 files new changesets 4ac2e3648604 changegroup hook: HG_HOOKNAME=changegroup HG_HOOKTYPE=changegroup HG_NODE=4ac2e3648604439c580c69b09ec9d93a88d93432 HG_NODE_LAST=4ac2e3648604439c580c69b09ec9d93a88d93432 HG_SOURCE=pull HG_TXNID=TXN:$ID$ HG_URL=http://localhost:$HGPORT/remote (run 'hg update' to get a working copy) trying to push $ hg update 1 files updated, 0 files merged, 0 files removed, 0 files unresolved $ echo more foo >> bar $ hg commit -m"test" $ hg push pushing to static-http://localhost:$HGPORT/remote abort: destination does not support push [255] trying clone -r $ cd .. $ hg clone -r doesnotexist static-http://localhost:$HGPORT/remote local0 abort: unknown revision 'doesnotexist'! [255] $ hg clone -r 0 static-http://localhost:$HGPORT/remote local0 adding changesets adding manifests adding file changes added 1 changesets with 2 changes to 2 files new changesets 02770d679fb8 updating to branch default 2 files updated, 0 files merged, 0 files removed, 0 files unresolved test with "/" URI (issue747) and subrepo $ hg init $ hg init sub $ touch sub/test $ hg -R sub commit -A -m "test" adding test $ hg -R sub tag not-empty $ echo sub=sub > .hgsub $ echo a > a $ hg add a .hgsub $ hg -q ci -ma $ hg clone static-http://localhost:$HGPORT/ local2 requesting all changes adding changesets adding manifests adding file changes added 1 changesets with 3 changes to 3 files new changesets a9ebfbe8e587 updating to branch default cloning subrepo sub from static-http://localhost:$HGPORT/sub requesting all changes adding changesets adding manifests adding file changes added 2 changesets with 2 changes to 2 files new changesets be090ea66256:322ea90975df 3 files updated, 0 files merged, 0 files removed, 0 files unresolved $ cd local2 $ hg verify checking changesets checking manifests crosschecking files in changesets and manifests checking files checked 1 changesets with 3 changes to 3 files checking subrepo links $ cat a a $ hg paths default = static-http://localhost:$HGPORT/ test with empty repo (issue965) $ cd .. $ hg init remotempty $ hg clone static-http://localhost:$HGPORT/remotempty local3 no changes found updating to branch default 0 files updated, 0 files merged, 0 files removed, 0 files unresolved $ cd local3 $ hg verify checking changesets checking manifests crosschecking files in changesets and manifests checking files checked 0 changesets with 0 changes to 0 files $ hg paths default = static-http://localhost:$HGPORT/remotempty test with non-repo $ cd .. $ mkdir notarepo $ hg clone static-http://localhost:$HGPORT/notarepo local3 abort: 'http://localhost:$HGPORT/notarepo' does not appear to be an hg repository! [255] Clone with tags and branches works $ hg init remote-with-names $ cd remote-with-names $ echo 0 > foo $ hg -q commit -A -m initial $ echo 1 > foo $ hg commit -m 'commit 1' $ hg -q up 0 $ hg branch mybranch marked working directory as branch mybranch (branches are permanent and global, did you want a bookmark?) $ echo 2 > foo $ hg commit -m 'commit 2 (mybranch)' $ hg tag -r 1 'default-tag' $ hg tag -r 2 'branch-tag' $ cd .. $ hg clone static-http://localhost:$HGPORT/remote-with-names local-with-names requesting all changes adding changesets adding manifests adding file changes added 5 changesets with 5 changes to 2 files (+1 heads) new changesets 68986213bd44:0c325bd2b5a7 updating to branch default 1 files updated, 0 files merged, 0 files removed, 0 files unresolved Clone a specific branch works $ hg clone -r mybranch static-http://localhost:$HGPORT/remote-with-names local-with-names-branch adding changesets adding manifests adding file changes added 4 changesets with 4 changes to 2 files new changesets 68986213bd44:0c325bd2b5a7 updating to branch mybranch 2 files updated, 0 files merged, 0 files removed, 0 files unresolved Clone a specific tag works $ hg clone -r default-tag static-http://localhost:$HGPORT/remote-with-names local-with-names-tag adding changesets adding manifests adding file changes added 2 changesets with 2 changes to 1 files new changesets 68986213bd44:4ee3fcef1c80 updating to branch default 1 files updated, 0 files merged, 0 files removed, 0 files unresolved $ killdaemons.py List of files accessed over HTTP: $ cat server.log | sed -n -e 's|.*GET \(/[^ ]*\).*|\1|p' | sort -u /.hg/bookmarks /.hg/bookmarks.current /.hg/cache/hgtagsfnodes1 /.hg/cache/rbc-names-v1 /.hg/cache/rbc-revs-v1 /.hg/requires /.hg/store/00changelog.i /.hg/store/00manifest.i /.hg/store/data/%7E2ehgsub.i /.hg/store/data/%7E2ehgsubstate.i /.hg/store/data/a.i /notarepo/.hg/00changelog.i /notarepo/.hg/requires /remote-with-names/.hg/bookmarks /remote-with-names/.hg/bookmarks.current /remote-with-names/.hg/cache/branch2-served /remote-with-names/.hg/cache/hgtagsfnodes1 /remote-with-names/.hg/cache/rbc-names-v1 /remote-with-names/.hg/cache/rbc-revs-v1 /remote-with-names/.hg/cache/tags2-served /remote-with-names/.hg/localtags /remote-with-names/.hg/requires /remote-with-names/.hg/store/00changelog.i /remote-with-names/.hg/store/00manifest.i /remote-with-names/.hg/store/data/%7E2ehgtags.i /remote-with-names/.hg/store/data/foo.i /remote/.hg/bookmarks /remote/.hg/bookmarks.current /remote/.hg/cache/branch2-base /remote/.hg/cache/branch2-immutable /remote/.hg/cache/branch2-served /remote/.hg/cache/hgtagsfnodes1 /remote/.hg/cache/rbc-names-v1 /remote/.hg/cache/rbc-revs-v1 /remote/.hg/cache/tags2-served /remote/.hg/localtags /remote/.hg/requires /remote/.hg/store/00changelog.i /remote/.hg/store/00manifest.i /remote/.hg/store/data/%7E2edotfile%20with%20spaces.i /remote/.hg/store/data/%7E2ehgtags.i /remote/.hg/store/data/bar.i /remote/.hg/store/data/quux.i /remotempty/.hg/bookmarks /remotempty/.hg/bookmarks.current /remotempty/.hg/requires /remotempty/.hg/store/00changelog.i /remotempty/.hg/store/00manifest.i /sub/.hg/bookmarks /sub/.hg/bookmarks.current /sub/.hg/cache/hgtagsfnodes1 /sub/.hg/cache/rbc-names-v1 /sub/.hg/cache/rbc-revs-v1 /sub/.hg/requires /sub/.hg/store/00changelog.i /sub/.hg/store/00manifest.i /sub/.hg/store/data/%7E2ehgtags.i /sub/.hg/store/data/test.i