view tests/test-bundle-type.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

bundle w/o type option

  $ hg init t1
  $ hg init t2
  $ cd t1
  $ echo blablablablabla > file.txt
  $ hg ci -Ama
  adding file.txt
  $ hg log | grep summary
  summary:     a
  $ hg bundle ../b1 ../t2
  searching for changes
  1 changesets found

  $ cd ../t2
  $ hg unbundle ../b1
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  new changesets c35a0f9217e6 (1 drafts)
  (run 'hg update' to get a working copy)
  $ hg up
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg log | grep summary
  summary:     a
  $ cd ..

Unknown compression type is rejected

  $ hg init t3
  $ cd t3
  $ hg -q unbundle ../b1
  $ hg bundle -a -t unknown out.hg
  abort: unknown is not a recognized bundle specification
  (see 'hg help bundlespec' for supported values for --type)
  [255]

  $ hg bundle -a -t unknown-v2 out.hg
  abort: unknown compression is not supported
  (see 'hg help bundlespec' for supported values for --type)
  [255]

  $ cd ..

test bundle types

  $ testbundle() {
  >   echo % test bundle type $1
  >   hg init t$1
  >   cd t1
  >   hg bundle -t $1 ../b$1 ../t$1
  >   f -q -B6 -D ../b$1; echo
  >   cd ../t$1
  >   hg debugbundle ../b$1
  >   hg debugbundle --spec ../b$1
  >   echo
  >   cd ..
  > }

  $ for t in "None" "bzip2" "gzip" "none-v2" "v2" "v1" "gzip-v1"; do
  >   testbundle $t
  > done
  % test bundle type None
  searching for changes
  1 changesets found
  HG20\x00\x00 (esc)
  Stream params: {}
  changegroup -- {nbchanges: 1, version: 02} (mandatory: True)
      c35a0f9217e65d1fdb90c936ffa7dbe679f83ddf
  cache:rev-branch-cache -- {} (mandatory: False)
  none-v2
  
  % test bundle type bzip2
  searching for changes
  1 changesets found
  HG20\x00\x00 (esc)
  Stream params: {Compression: BZ}
  changegroup -- {nbchanges: 1, version: 02} (mandatory: True)
      c35a0f9217e65d1fdb90c936ffa7dbe679f83ddf
  cache:rev-branch-cache -- {} (mandatory: False)
  bzip2-v2
  
  % test bundle type gzip
  searching for changes
  1 changesets found
  HG20\x00\x00 (esc)
  Stream params: {Compression: GZ}
  changegroup -- {nbchanges: 1, version: 02} (mandatory: True)
      c35a0f9217e65d1fdb90c936ffa7dbe679f83ddf
  cache:rev-branch-cache -- {} (mandatory: False)
  gzip-v2
  
  % test bundle type none-v2
  searching for changes
  1 changesets found
  HG20\x00\x00 (esc)
  Stream params: {}
  changegroup -- {nbchanges: 1, version: 02} (mandatory: True)
      c35a0f9217e65d1fdb90c936ffa7dbe679f83ddf
  cache:rev-branch-cache -- {} (mandatory: False)
  none-v2
  
  % test bundle type v2
  searching for changes
  1 changesets found
  HG20\x00\x00 (esc)
  Stream params: {Compression: BZ}
  changegroup -- {nbchanges: 1, version: 02} (mandatory: True)
      c35a0f9217e65d1fdb90c936ffa7dbe679f83ddf
  cache:rev-branch-cache -- {} (mandatory: False)
  bzip2-v2
  
  % test bundle type v1
  searching for changes
  1 changesets found
  HG10BZ
  c35a0f9217e65d1fdb90c936ffa7dbe679f83ddf
  bzip2-v1
  
  % test bundle type gzip-v1
  searching for changes
  1 changesets found
  HG10GZ
  c35a0f9217e65d1fdb90c936ffa7dbe679f83ddf
  gzip-v1
  

Compression level can be adjusted for bundle2 bundles

  $ hg init test-complevel
  $ cd test-complevel

  $ cat > file0 << EOF
  > this is a file
  > with some text
  > and some more text
  > and other content
  > EOF
  $ cat > file1 << EOF
  > this is another file
  > with some other content
  > and repeated, repeated, repeated, repeated content
  > EOF
  $ hg -q commit -A -m initial

  $ hg bundle -a -t gzip-v2 gzip-v2.hg
  1 changesets found
  $ f --size gzip-v2.hg
  gzip-v2.hg: size=468

  $ hg --config experimental.bundlecomplevel=1 bundle -a -t gzip-v2 gzip-v2-level1.hg
  1 changesets found
  $ f --size gzip-v2-level1.hg
  gzip-v2-level1.hg: size=475

  $ hg --config experimental.bundlecomplevel.gzip=1 --config experimental.bundlelevel=9 bundle -a -t gzip-v2 gzip-v2-level1.hg
  1 changesets found
  $ f --size gzip-v2-level1.hg
  gzip-v2-level1.hg: size=475

  $ cd ..

#if zstd

  $ for t in "zstd" "zstd-v2"; do
  >   testbundle $t
  > done
  % test bundle type zstd
  searching for changes
  1 changesets found
  HG20\x00\x00 (esc)
  Stream params: {Compression: ZS}
  changegroup -- {nbchanges: 1, version: 02} (mandatory: True)
      c35a0f9217e65d1fdb90c936ffa7dbe679f83ddf
  cache:rev-branch-cache -- {} (mandatory: False)
  zstd-v2
  
  % test bundle type zstd-v2
  searching for changes
  1 changesets found
  HG20\x00\x00 (esc)
  Stream params: {Compression: ZS}
  changegroup -- {nbchanges: 1, version: 02} (mandatory: True)
      c35a0f9217e65d1fdb90c936ffa7dbe679f83ddf
  cache:rev-branch-cache -- {} (mandatory: False)
  zstd-v2
  

Explicit request for zstd on non-generaldelta repos

  $ hg --config format.usegeneraldelta=false init nogd
  $ hg -q -R nogd pull t1
  $ hg -R nogd bundle -a -t zstd nogd-zstd
  1 changesets found

zstd-v1 always fails

  $ hg -R tzstd bundle -a -t zstd-v1 zstd-v1
  abort: compression engine zstd is not supported on v1 bundles
  (see 'hg help bundlespec' for supported values for --type)
  [255]

#else

zstd is a valid engine but isn't available

  $ hg -R t1 bundle -a -t zstd irrelevant.hg
  abort: compression engine zstd could not be loaded
  [255]

#endif

test garbage file

  $ echo garbage > bgarbage
  $ hg init tgarbage
  $ cd tgarbage
  $ hg pull ../bgarbage
  pulling from ../bgarbage
  abort: ../bgarbage: not a Mercurial bundle
  [255]
  $ cd ..

test invalid bundle type

  $ cd t1
  $ hg bundle -a -t garbage ../bgarbage
  abort: garbage is not a recognized bundle specification
  (see 'hg help bundlespec' for supported values for --type)
  [255]
  $ cd ..