view contrib/packaging/mercurial.spec @ 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

%global emacs_lispdir %{_datadir}/emacs/site-lisp

%define withpython %{nil}

%if "%{?withpython}"

%global pythonver %{withpython}
%global pythonname Python-%{withpython}
%global docutilsname docutils-0.14
%global docutilsmd5 c53768d63db3873b7d452833553469de
%global pythonhg python-hg
%global hgpyprefix /opt/%{pythonhg}
# byte compilation will fail on some some Python /test/ files
%global _python_bytecompile_errors_terminate_build 0

%else

%global pythonver %(python -c 'import sys;print ".".join(map(str, sys.version_info[:2]))')

%endif

Summary: A fast, lightweight Source Control Management system
Name: mercurial
Version: snapshot
Release: 0
License: GPLv2+
Group: Development/Tools
URL: https://mercurial-scm.org/
Source0: %{name}-%{version}-%{release}.tar.gz
%if "%{?withpython}"
Source1: %{pythonname}.tgz
Source2: %{docutilsname}.tar.gz
%endif
BuildRoot: %{_tmppath}/%{name}-%{version}-%{release}-root

BuildRequires: make, gcc, gettext
%if "%{?withpython}"
BuildRequires: readline-devel, openssl-devel, ncurses-devel, zlib-devel, bzip2-devel
%else
BuildRequires: python >= 2.7, python-devel, python-docutils >= 0.5
Requires: python >= 2.7
%endif
# The hgk extension uses the wish tcl interpreter, but we don't enforce it
#Requires: tk

%description
Mercurial is a fast, lightweight source control management system designed
for efficient handling of very large distributed projects.

%prep

%if "%{?withpython}"
%setup -q -n mercurial-%{version}-%{release} -a1 -a2
# despite the comments in cgi.py, we do this to prevent rpmdeps from picking /usr/local/bin/python up
sed -i '1c#! /usr/bin/env python' %{pythonname}/Lib/cgi.py
%else
%setup -q -n mercurial-%{version}-%{release}
%endif

%build

%if "%{?withpython}"

PYPATH=$PWD/%{pythonname}
cd $PYPATH
./configure --prefix=%{hgpyprefix}
make all %{?_smp_mflags}
cd -

cd %{docutilsname}
LD_LIBRARY_PATH=$PYPATH $PYPATH/python setup.py build
cd -

# verify Python environment
LD_LIBRARY_PATH=$PYPATH PYTHONPATH=$PWD/%{docutilsname} $PYPATH/python -c 'import sys, zlib, bz2, ssl, curses, readline'

# set environment for make
export PATH=$PYPATH:$PATH
export LD_LIBRARY_PATH=$PYPATH
export CFLAGS="-L $PYPATH"
export PYTHONPATH=$PWD/%{docutilsname}

%endif

make all
make -C contrib/chg

%install
rm -rf $RPM_BUILD_ROOT

%if "%{?withpython}"

PYPATH=$PWD/%{pythonname}
cd $PYPATH
make install DESTDIR=$RPM_BUILD_ROOT
# these .a are not necessary and they are readonly and strip fails - kill them!
rm -f %{buildroot}%{hgpyprefix}/lib/{,python2.*/config}/libpython2.*.a
cd -

cd %{docutilsname}
LD_LIBRARY_PATH=$PYPATH $PYPATH/python setup.py install --root="$RPM_BUILD_ROOT"
cd -

PATH=$PYPATH:$PATH LD_LIBRARY_PATH=$PYPATH make install DESTDIR=$RPM_BUILD_ROOT PREFIX=%{hgpyprefix} MANDIR=%{_mandir}
mkdir -p $RPM_BUILD_ROOT%{_bindir}
( cd $RPM_BUILD_ROOT%{_bindir}/ && ln -s ../..%{hgpyprefix}/bin/hg . )
( cd $RPM_BUILD_ROOT%{_bindir}/ && ln -s ../..%{hgpyprefix}/bin/python2.? %{pythonhg} )

%else

make install DESTDIR=$RPM_BUILD_ROOT PREFIX=%{_prefix} MANDIR=%{_mandir}

%endif

install -m 755 contrib/chg/chg $RPM_BUILD_ROOT%{_bindir}/
install -m 755 contrib/hgk $RPM_BUILD_ROOT%{_bindir}/
install -m 755 contrib/hg-ssh $RPM_BUILD_ROOT%{_bindir}/

bash_completion_dir=$RPM_BUILD_ROOT%{_sysconfdir}/bash_completion.d
mkdir -p $bash_completion_dir
install -m 644 contrib/bash_completion $bash_completion_dir/mercurial.sh

zsh_completion_dir=$RPM_BUILD_ROOT%{_datadir}/zsh/site-functions
mkdir -p $zsh_completion_dir
install -m 644 contrib/zsh_completion $zsh_completion_dir/_mercurial

mkdir -p $RPM_BUILD_ROOT%{emacs_lispdir}
install -m 644 contrib/mercurial.el $RPM_BUILD_ROOT%{emacs_lispdir}/
install -m 644 contrib/mq.el $RPM_BUILD_ROOT%{emacs_lispdir}/

mkdir -p $RPM_BUILD_ROOT/%{_sysconfdir}/mercurial/hgrc.d

%clean
rm -rf $RPM_BUILD_ROOT

%files
%defattr(-,root,root,-)
%doc CONTRIBUTORS COPYING doc/README doc/hg*.txt doc/hg*.html *.cgi contrib/*.fcgi
%doc %attr(644,root,root) %{_mandir}/man?/hg*
%doc %attr(644,root,root) contrib/*.svg
%dir %{_datadir}/zsh/
%dir %{_datadir}/zsh/site-functions/
%{_datadir}/zsh/site-functions/_mercurial
%dir %{_datadir}/emacs/site-lisp/
%{_datadir}/emacs/site-lisp/mercurial.el
%{_datadir}/emacs/site-lisp/mq.el
%{_bindir}/hg
%{_bindir}/chg
%{_bindir}/hgk
%{_bindir}/hg-ssh
%dir %{_sysconfdir}/bash_completion.d/
%config(noreplace) %{_sysconfdir}/bash_completion.d/mercurial.sh
%dir %{_sysconfdir}/mercurial
%dir %{_sysconfdir}/mercurial/hgrc.d
%if "%{?withpython}"
%{_bindir}/%{pythonhg}
%{hgpyprefix}
%else
%{_libdir}/python%{pythonver}/site-packages/%{name}-*-py%{pythonver}.egg-info
%{_libdir}/python%{pythonver}/site-packages/%{name}
%{_libdir}/python%{pythonver}/site-packages/hgext
%{_libdir}/python%{pythonver}/site-packages/hgext3rd
%{_libdir}/python%{pythonver}/site-packages/hgdemandimport
%endif