view tests/test-infinitepush.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

#require no-reposimplestore

Testing infinipush extension and the confi options provided by it

Setup

  $ . "$TESTDIR/library-infinitepush.sh"
  $ cp $HGRCPATH $TESTTMP/defaulthgrc
  $ setupcommon
  $ hg init repo
  $ cd repo
  $ setupserver
  $ echo initialcommit > initialcommit
  $ hg ci -Aqm "initialcommit"
  $ hg phase --public .

  $ cd ..
  $ hg clone ssh://user@dummy/repo client -q

Create two heads. Push first head alone, then two heads together. Make sure that
multihead push works.
  $ cd client
  $ echo multihead1 > multihead1
  $ hg add multihead1
  $ hg ci -m "multihead1"
  $ hg up null
  0 files updated, 0 files merged, 2 files removed, 0 files unresolved
  $ echo multihead2 > multihead2
  $ hg ci -Am "multihead2"
  adding multihead2
  created new head
  $ hg push -r . --bundle-store
  pushing to ssh://user@dummy/repo
  searching for changes
  remote: pushing 1 commit:
  remote:     ee4802bf6864  multihead2
  $ hg push -r '1:2' --bundle-store
  pushing to ssh://user@dummy/repo
  searching for changes
  remote: pushing 2 commits:
  remote:     bc22f9a30a82  multihead1
  remote:     ee4802bf6864  multihead2
  $ scratchnodes
  bc22f9a30a821118244deacbd732e394ed0b686c ab1bc557aa090a9e4145512c734b6e8a828393a5
  ee4802bf6864326a6b3dcfff5a03abc2a0a69b8f ab1bc557aa090a9e4145512c734b6e8a828393a5

Create two new scratch bookmarks
  $ hg up 0
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ echo scratchfirstpart > scratchfirstpart
  $ hg ci -Am "scratchfirstpart"
  adding scratchfirstpart
  created new head
  $ hg push -r . -B scratch/firstpart
  pushing to ssh://user@dummy/repo
  searching for changes
  remote: pushing 1 commit:
  remote:     176993b87e39  scratchfirstpart
  $ hg up 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ echo scratchsecondpart > scratchsecondpart
  $ hg ci -Am "scratchsecondpart"
  adding scratchsecondpart
  created new head
  $ hg push -r . -B scratch/secondpart
  pushing to ssh://user@dummy/repo
  searching for changes
  remote: pushing 1 commit:
  remote:     8db3891c220e  scratchsecondpart

Pull two bookmarks from the second client
  $ cd ..
  $ hg clone ssh://user@dummy/repo client2 -q
  $ cd client2
  $ hg pull -B scratch/firstpart -B scratch/secondpart
  pulling from ssh://user@dummy/repo
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files (+1 heads)
  new changesets * (glob)
  (run 'hg heads' to see heads, 'hg merge' to merge)
  $ hg log -r scratch/secondpart -T '{node}'
  8db3891c220e216f6da214e8254bd4371f55efca (no-eol)
  $ hg log -r scratch/firstpart -T '{node}'
  176993b87e39bd88d66a2cccadabe33f0b346339 (no-eol)
Make two commits to the scratch branch

  $ echo testpullbycommithash1 > testpullbycommithash1
  $ hg ci -Am "testpullbycommithash1"
  adding testpullbycommithash1
  created new head
  $ hg log -r '.' -T '{node}\n' > ../testpullbycommithash1
  $ echo testpullbycommithash2 > testpullbycommithash2
  $ hg ci -Aqm "testpullbycommithash2"
  $ hg push -r . -B scratch/mybranch -q

Create third client and pull by commit hash.
Make sure testpullbycommithash2 has not fetched
  $ cd ..
  $ hg clone ssh://user@dummy/repo client3 -q
  $ cd client3
  $ hg pull -r `cat ../testpullbycommithash1`
  pulling from ssh://user@dummy/repo
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  new changesets 33910bfe6ffe (1 drafts)
  (run 'hg update' to get a working copy)
  $ hg log -G -T '{desc} {phase} {bookmarks}'
  o  testpullbycommithash1 draft
  |
  @  initialcommit public
  
Make public commit in the repo and pull it.
Make sure phase on the client is public.
  $ cd ../repo
  $ echo publiccommit > publiccommit
  $ hg ci -Aqm "publiccommit"
  $ hg phase --public .
  $ cd ../client3
  $ hg pull
  pulling from ssh://user@dummy/repo
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files (+1 heads)
  new changesets a79b6597f322
  (run 'hg heads' to see heads, 'hg merge' to merge)
  $ hg log -G -T '{desc} {phase} {bookmarks} {node|short}'
  o  publiccommit public  a79b6597f322
  |
  | o  testpullbycommithash1 draft  33910bfe6ffe
  |/
  @  initialcommit public  67145f466344
  
  $ hg up a79b6597f322
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo scratchontopofpublic > scratchontopofpublic
  $ hg ci -Aqm "scratchontopofpublic"
  $ hg push -r . -B scratch/scratchontopofpublic
  pushing to ssh://user@dummy/repo
  searching for changes
  remote: pushing 1 commit:
  remote:     c70aee6da07d  scratchontopofpublic
  $ cd ../client2
  $ hg pull -B scratch/scratchontopofpublic
  pulling from ssh://user@dummy/repo
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files (+1 heads)
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  new changesets a79b6597f322:c70aee6da07d (1 drafts)
  (run 'hg heads .' to see heads, 'hg merge' to merge)
  $ hg log -r scratch/scratchontopofpublic -T '{phase}'
  draft (no-eol)