Mercurial > hg
view tests/test-convert-cvs-synthetic.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 | 96529f81e2e9 |
children | e5e5ee2b60e4 |
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#require cvs112 This feature requires use of builtin cvsps! $ echo "[extensions]" >> $HGRCPATH $ echo "convert = " >> $HGRCPATH create cvs repository with one project $ mkdir cvsrepo $ cd cvsrepo $ CVSROOT=`pwd` $ export CVSROOT $ CVS_OPTIONS=-f $ export CVS_OPTIONS $ cd .. $ rmdir cvsrepo $ cvscall() > { > cvs -f "$@" > } output of 'cvs ci' varies unpredictably, so just discard it $ cvsci() > { > sleep 1 > cvs -f ci "$@" >/dev/null > } $ cvscall -d "$CVSROOT" init $ mkdir cvsrepo/proj $ cvscall -q co proj create file1 on the trunk $ cd proj $ touch file1 $ cvscall -Q add file1 $ cvsci -m"add file1 on trunk" file1 create two branches $ cvscall -q tag -b v1_0 T file1 $ cvscall -q tag -b v1_1 T file1 create file2 on branch v1_0 $ cvscall -Q up -rv1_0 $ touch file2 $ cvscall -Q add file2 $ cvsci -m"add file2" file2 create file3, file4 on branch v1_1 $ cvscall -Q up -rv1_1 $ touch file3 $ touch file4 $ cvscall -Q add file3 file4 $ cvsci -m"add file3, file4 on branch v1_1" file3 file4 merge file2 from v1_0 to v1_1 $ cvscall -Q up -jv1_0 $ cvsci -m"MERGE from v1_0: add file2" cvs commit: Examining . Step things up a notch: now we make the history really hairy, with changes bouncing back and forth between trunk and v1_2 and merges going both ways. (I.e., try to model the real world.) create branch v1_2 $ cvscall -Q up -A $ cvscall -q tag -b v1_2 T file1 create file5 on branch v1_2 $ cvscall -Q up -rv1_2 $ touch file5 $ cvs -Q add file5 $ cvsci -m"add file5 on v1_2" cvs commit: Examining . create file6 on trunk post-v1_2 $ cvscall -Q up -A $ touch file6 $ cvscall -Q add file6 $ cvsci -m"add file6 on trunk post-v1_2" cvs commit: Examining . merge file5 from v1_2 to trunk $ cvscall -Q up -A $ cvscall -Q up -jv1_2 file5 $ cvsci -m"MERGE from v1_2: add file5" cvs commit: Examining . merge file6 from trunk to v1_2 $ cvscall -Q up -rv1_2 $ cvscall up -jHEAD file6 U file6 $ cvsci -m"MERGE from HEAD: add file6" cvs commit: Examining . cvs rlog output $ cvscall -q rlog proj | egrep '^(RCS file|revision)' RCS file: $TESTTMP/cvsrepo/proj/file1,v revision 1.1 RCS file: $TESTTMP/cvsrepo/proj/Attic/file2,v revision 1.1 revision 1.1.4.2 revision 1.1.4.1 revision 1.1.2.1 RCS file: $TESTTMP/cvsrepo/proj/Attic/file3,v revision 1.1 revision 1.1.2.1 RCS file: $TESTTMP/cvsrepo/proj/Attic/file4,v revision 1.1 revision 1.1.2.1 RCS file: $TESTTMP/cvsrepo/proj/file5,v revision 1.2 revision 1.1 revision 1.1.2.1 RCS file: $TESTTMP/cvsrepo/proj/file6,v revision 1.1 revision 1.1.2.2 revision 1.1.2.1 convert to hg (#1) $ cd .. $ hg convert --datesort proj proj.hg initializing destination proj.hg repository connecting to $TESTTMP/cvsrepo scanning source... collecting CVS rlog 15 log entries creating changesets 9 changeset entries sorting... converting... 8 add file1 on trunk 7 add file2 6 MERGE from v1_0: add file2 5 file file3 was initially added on branch v1_1. 4 add file3, file4 on branch v1_1 3 add file5 on v1_2 2 add file6 on trunk post-v1_2 1 MERGE from HEAD: add file6 0 MERGE from v1_2: add file5 hg log -G output (#1) $ hg -R proj.hg log -G --template "{rev} {desc}\n" o 8 MERGE from v1_2: add file5 | | o 7 MERGE from HEAD: add file6 | | o | 6 add file6 on trunk post-v1_2 | | | o 5 add file5 on v1_2 | | | | o 4 add file3, file4 on branch v1_1 | | | o | | 3 file file3 was initially added on branch v1_1. |/ / | o 2 MERGE from v1_0: add file2 |/ | o 1 add file2 |/ o 0 add file1 on trunk convert to hg (#2: with merge detection) $ hg convert \ > --config convert.cvsps.mergefrom='"^MERGE from (\S+):"' \ > --datesort \ > proj proj.hg2 initializing destination proj.hg2 repository connecting to $TESTTMP/cvsrepo scanning source... collecting CVS rlog 15 log entries creating changesets 9 changeset entries sorting... converting... 8 add file1 on trunk 7 add file2 6 MERGE from v1_0: add file2 5 file file3 was initially added on branch v1_1. 4 add file3, file4 on branch v1_1 3 add file5 on v1_2 2 add file6 on trunk post-v1_2 1 MERGE from HEAD: add file6 0 MERGE from v1_2: add file5 hg log -G output (#2) $ hg -R proj.hg2 log -G --template "{rev} {desc}\n" o 8 MERGE from v1_2: add file5 | | o 7 MERGE from HEAD: add file6 | | o | 6 add file6 on trunk post-v1_2 | | | o 5 add file5 on v1_2 | | | | o 4 add file3, file4 on branch v1_1 | | | o | | 3 file file3 was initially added on branch v1_1. |/ / | o 2 MERGE from v1_0: add file2 |/ | o 1 add file2 |/ o 0 add file1 on trunk