view tests/test-export.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

  $ hg init repo
  $ cd repo
  $ touch foo
  $ hg add foo
  $ for i in 0 1 2 3 4 5 6 7 8 9 10 11; do
  >    echo "foo-$i" >> foo
  >    hg ci -m "foo-$i"
  > done

  $ for out in "%nof%N" "%%%H" "%b-%R" "%h" "%r" "%m"; do
  >    echo
  >    echo "# foo-$out.patch"
  >    hg export -v -o "foo-$out.patch" 2:tip
  > done
  
  # foo-%nof%N.patch
  exporting patches:
  foo-01of10.patch
  foo-02of10.patch
  foo-03of10.patch
  foo-04of10.patch
  foo-05of10.patch
  foo-06of10.patch
  foo-07of10.patch
  foo-08of10.patch
  foo-09of10.patch
  foo-10of10.patch
  
  # foo-%%%H.patch
  exporting patches:
  foo-%617188a1c80f869a7b66c85134da88a6fb145f67.patch
  foo-%dd41a5ff707a5225204105611ba49cc5c229d55f.patch
  foo-%f95a5410f8664b6e1490a4af654e4b7d41a7b321.patch
  foo-%4346bcfde53b4d9042489078bcfa9c3e28201db2.patch
  foo-%afda8c3a009cc99449a05ad8aa4655648c4ecd34.patch
  foo-%35284ce2b6b99c9d2ac66268fe99e68e1974e1aa.patch
  foo-%9688c41894e6931305fa7165a37f6568050b4e9b.patch
  foo-%747d3c68f8ec44bb35816bfcd59aeb50b9654c2f.patch
  foo-%5f17a83f5fbd9414006a5e563eab4c8a00729efd.patch
  foo-%f3acbafac161ec68f1598af38f794f28847ca5d3.patch
  
  # foo-%b-%R.patch
  exporting patches:
  foo-repo-2.patch
  foo-repo-3.patch
  foo-repo-4.patch
  foo-repo-5.patch
  foo-repo-6.patch
  foo-repo-7.patch
  foo-repo-8.patch
  foo-repo-9.patch
  foo-repo-10.patch
  foo-repo-11.patch
  
  # foo-%h.patch
  exporting patches:
  foo-617188a1c80f.patch
  foo-dd41a5ff707a.patch
  foo-f95a5410f866.patch
  foo-4346bcfde53b.patch
  foo-afda8c3a009c.patch
  foo-35284ce2b6b9.patch
  foo-9688c41894e6.patch
  foo-747d3c68f8ec.patch
  foo-5f17a83f5fbd.patch
  foo-f3acbafac161.patch
  
  # foo-%r.patch
  exporting patches:
  foo-02.patch
  foo-03.patch
  foo-04.patch
  foo-05.patch
  foo-06.patch
  foo-07.patch
  foo-08.patch
  foo-09.patch
  foo-10.patch
  foo-11.patch
  
  # foo-%m.patch
  exporting patches:
  foo-foo_2.patch
  foo-foo_3.patch
  foo-foo_4.patch
  foo-foo_5.patch
  foo-foo_6.patch
  foo-foo_7.patch
  foo-foo_8.patch
  foo-foo_9.patch
  foo-foo_10.patch
  foo-foo_11.patch

Doing it again clobbers the files rather than appending:
  $ hg export -v -o "foo-%m.patch" 2:3
  exporting patches:
  foo-foo_2.patch
  foo-foo_3.patch
  $ grep HG foo-foo_2.patch | wc -l
  \s*1 (re)
  $ grep HG foo-foo_3.patch | wc -l
  \s*1 (re)

Using bookmarks:

  $ hg book -f -r 9 @
  $ hg book -f -r 11 test
  $ hg export -B test
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID 5f17a83f5fbd9414006a5e563eab4c8a00729efd
  # Parent  747d3c68f8ec44bb35816bfcd59aeb50b9654c2f
  foo-10
  
  diff -r 747d3c68f8ec -r 5f17a83f5fbd foo
  --- a/foo	Thu Jan 01 00:00:00 1970 +0000
  +++ b/foo	Thu Jan 01 00:00:00 1970 +0000
  @@ -8,3 +8,4 @@
   foo-7
   foo-8
   foo-9
  +foo-10
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID f3acbafac161ec68f1598af38f794f28847ca5d3
  # Parent  5f17a83f5fbd9414006a5e563eab4c8a00729efd
  foo-11
  
  diff -r 5f17a83f5fbd -r f3acbafac161 foo
  --- a/foo	Thu Jan 01 00:00:00 1970 +0000
  +++ b/foo	Thu Jan 01 00:00:00 1970 +0000
  @@ -9,3 +9,4 @@
   foo-8
   foo-9
   foo-10
  +foo-11

Exporting 4 changesets to a file:

  $ hg export -o export_internal 1 2 3 4
  $ grep HG export_internal | wc -l
  \s*4 (re)

Doing it again clobbers the file rather than appending:
  $ hg export -o export_internal 1 2 3 4
  $ grep HG export_internal | wc -l
  \s*4 (re)

Exporting 4 changesets to stdout:

  $ hg export 1 2 3 4 | grep HG | wc -l
  \s*4 (re)

Exporting revision -2 to a file:

  $ hg export -- -2
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID 5f17a83f5fbd9414006a5e563eab4c8a00729efd
  # Parent  747d3c68f8ec44bb35816bfcd59aeb50b9654c2f
  foo-10
  
  diff -r 747d3c68f8ec -r 5f17a83f5fbd foo
  --- a/foo	Thu Jan 01 00:00:00 1970 +0000
  +++ b/foo	Thu Jan 01 00:00:00 1970 +0000
  @@ -8,3 +8,4 @@
   foo-7
   foo-8
   foo-9
  +foo-10

Exporting wdir revision:

  $ echo "foo-wdir" >> foo
  $ hg export 'wdir()'
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID ffffffffffffffffffffffffffffffffffffffff
  # Parent  f3acbafac161ec68f1598af38f794f28847ca5d3
  
  
  diff -r f3acbafac161 foo
  --- a/foo	Thu Jan 01 00:00:00 1970 +0000
  +++ b/foo	Thu Jan 01 00:00:00 1970 +0000
  @@ -10,3 +10,4 @@
   foo-9
   foo-10
   foo-11
  +foo-wdir
  $ hg revert -q foo

Templated output to stdout:

  $ hg export -Tjson 0
  [
   {
    "branch": "default",
    "date": [0, 0],
    "desc": "foo-0",
    "diff": "diff -r 000000000000 -r 871558de6af2 foo\n--- /dev/null\tThu Jan 01 00:00:00 1970 +0000\n+++ b/foo\tThu Jan 01 00:00:00 1970 +0000\n@@ -0,0 +1,1 @@\n+foo-0\n",
    "node": "871558de6af2e8c244222f8eea69b782c94ce3df",
    "parents": [],
    "user": "test"
   }
  ]

Templated output to single file:

  $ hg export -Tjson 0:1 -o out.json
  $ cat out.json
  [
   {
    "branch": "default",
    "date": [0, 0],
    "desc": "foo-0",
    "diff": "diff -r 000000000000 -r 871558de6af2 foo\n--- /dev/null\tThu Jan 01 00:00:00 1970 +0000\n+++ b/foo\tThu Jan 01 00:00:00 1970 +0000\n@@ -0,0 +1,1 @@\n+foo-0\n",
    "node": "871558de6af2e8c244222f8eea69b782c94ce3df",
    "parents": [],
    "user": "test"
   },
   {
    "branch": "default",
    "date": [0, 0],
    "desc": "foo-1",
    "diff": "diff -r 871558de6af2 -r d1c9656e973c foo\n--- a/foo\tThu Jan 01 00:00:00 1970 +0000\n+++ b/foo\tThu Jan 01 00:00:00 1970 +0000\n@@ -1,1 +1,2 @@\n foo-0\n+foo-1\n",
    "node": "d1c9656e973cfb5aebd5499bbd2cb350e3b12266",
    "parents": ["871558de6af2e8c244222f8eea69b782c94ce3df"],
    "user": "test"
   }
  ]

Templated output to multiple files:

  $ hg export -Tjson 0:1 -o 'out-{rev}.json'
  $ cat out-0.json
  [
   {
    "branch": "default",
    "date": [0, 0],
    "desc": "foo-0",
    "diff": "diff -r 000000000000 -r 871558de6af2 foo\n--- /dev/null\tThu Jan 01 00:00:00 1970 +0000\n+++ b/foo\tThu Jan 01 00:00:00 1970 +0000\n@@ -0,0 +1,1 @@\n+foo-0\n",
    "node": "871558de6af2e8c244222f8eea69b782c94ce3df",
    "parents": [],
    "user": "test"
   }
  ]
  $ cat out-1.json
  [
   {
    "branch": "default",
    "date": [0, 0],
    "desc": "foo-1",
    "diff": "diff -r 871558de6af2 -r d1c9656e973c foo\n--- a/foo\tThu Jan 01 00:00:00 1970 +0000\n+++ b/foo\tThu Jan 01 00:00:00 1970 +0000\n@@ -1,1 +1,2 @@\n foo-0\n+foo-1\n",
    "node": "d1c9656e973cfb5aebd5499bbd2cb350e3b12266",
    "parents": ["871558de6af2e8c244222f8eea69b782c94ce3df"],
    "user": "test"
   }
  ]

Template keywrods:

  $ hg export 0 -T '# {node|shortest}\n\n{diff}'
  # 8715
  
  diff -r 000000000000 -r 871558de6af2 foo
  --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
  +++ b/foo	Thu Jan 01 00:00:00 1970 +0000
  @@ -0,0 +1,1 @@
  +foo-0

No filename should be printed if stdout is specified explicitly:

  $ hg export -v 1 -o -
  exporting patch:
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID d1c9656e973cfb5aebd5499bbd2cb350e3b12266
  # Parent  871558de6af2e8c244222f8eea69b782c94ce3df
  foo-1
  
  diff -r 871558de6af2 -r d1c9656e973c foo
  --- a/foo	Thu Jan 01 00:00:00 1970 +0000
  +++ b/foo	Thu Jan 01 00:00:00 1970 +0000
  @@ -1,1 +1,2 @@
   foo-0
  +foo-1

Checking if only alphanumeric characters are used in the file name (%m option):

  $ echo "line" >> foo
  $ hg commit -m " !\"#$%&(,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]"'^'"_\`abcdefghijklmnopqrstuvwxyz{|}~"
  $ hg export -v -o %m.patch tip
  exporting patch:
  ___________0123456789_______ABCDEFGHIJKLMNOPQRSTUVWXYZ______abcdefghijklmnopqrstuvwxyz____.patch

Template fragments in file name:

  $ hg export -v -o '{node|shortest}.patch' tip
  exporting patch:
  197e.patch

Backslash should be preserved because it is a directory separator on Windows:

  $ mkdir out
  $ hg export -v -o 'out\{node|shortest}.patch' tip
  exporting patch:
  out\197e.patch

Still backslash is taken as an escape character in inner template strings:

  $ hg export -v -o '{"out\{foo}.patch"}' tip
  exporting patch:
  out{foo}.patch

Invalid pattern in file name:

  $ hg export -o '%x.patch' tip
  abort: invalid format spec '%x' in output filename
  [255]
  $ hg export -o '%' tip
  abort: incomplete format spec in output filename
  [255]
  $ hg export -o '%{"foo"}' tip
  abort: incomplete format spec in output filename
  [255]
  $ hg export -o '%m{' tip
  hg: parse error at 3: unterminated template expansion
  (%m{
      ^ here)
  [255]
  $ hg export -o '%\' tip
  abort: invalid format spec '%\' in output filename
  [255]
  $ hg export -o '\%' tip
  abort: incomplete format spec in output filename
  [255]

Catch exporting unknown revisions (especially empty revsets, see issue3353)

  $ hg export
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID 197ecd81a57f760b54f34a58817ad5b04991fa47
  # Parent  f3acbafac161ec68f1598af38f794f28847ca5d3
   !"#$%&(,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~
  
  diff -r f3acbafac161 -r 197ecd81a57f foo
  --- a/foo	Thu Jan 01 00:00:00 1970 +0000
  +++ b/foo	Thu Jan 01 00:00:00 1970 +0000
  @@ -10,3 +10,4 @@
   foo-9
   foo-10
   foo-11
  +line

  $ hg export ""
  hg: parse error: empty query
  [255]
  $ hg export 999
  abort: unknown revision '999'!
  [255]
  $ hg export "not all()"
  abort: export requires at least one changeset
  [255]

Check for color output
  $ cat <<EOF >> $HGRCPATH
  > [color]
  > mode = ansi
  > [extensions]
  > color =
  > EOF

  $ hg export --color always --nodates tip
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID * (glob)
  # Parent * (glob)
   !"#$%&(,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~
  
  \x1b[0;1mdiff -r f3acbafac161 -r 197ecd81a57f foo\x1b[0m (esc)
  \x1b[0;31;1m--- a/foo\x1b[0m (esc)
  \x1b[0;32;1m+++ b/foo\x1b[0m (esc)
  \x1b[0;35m@@ -10,3 +10,4 @@\x1b[0m (esc)
   foo-9
   foo-10
   foo-11
  \x1b[0;32m+line\x1b[0m (esc)


  $ cd ..