view tests/test-convert-hg-sink.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

  $ cat >> $HGRCPATH <<EOF
  > [extensions]
  > convert=
  > [convert]
  > hg.saverev=False
  > EOF
  $ hg init orig
  $ cd orig
  $ echo foo > foo
  $ echo bar > bar
  $ hg ci -qAm 'add foo and bar'
  $ hg rm foo
  $ hg ci -m 'remove foo'
  $ mkdir foo
  $ echo file > foo/file
  $ hg ci -qAm 'add foo/file'
  $ hg tag some-tag
  $ hg tag -l local-tag
  $ echo '1234567890123456789012345678901234567890 missing_tag' >> .hgtags
  $ hg ci -m 'add a missing tag'
  $ hg log
  changeset:   4:3fb95ee23a66
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     add a missing tag
  
  changeset:   3:593cbf6fb2b4
  tag:         local-tag
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     Added tag some-tag for changeset ad681a868e44
  
  changeset:   2:ad681a868e44
  tag:         some-tag
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     add foo/file
  
  changeset:   1:cbba8ecc03b7
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     remove foo
  
  changeset:   0:327daa9251fa
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     add foo and bar
  
  $ hg phase --public -r tip
  $ cd ..
  $ hg convert orig new 2>&1 | grep -v 'subversion python bindings could not be loaded'
  initializing destination new repository
  scanning source...
  sorting...
  converting...
  4 add foo and bar
  3 remove foo
  2 add foo/file
  1 Added tag some-tag for changeset ad681a868e44
  0 add a missing tag
  missing tag entry: "1234567890123456789012345678901234567890 missing_tag"
  $ cd new
  $ hg log -G --template '{rev} {node|short} ({phase}) "{desc}"\n'
  o  4 3fb95ee23a66 (public) "add a missing tag"
  |
  o  3 593cbf6fb2b4 (public) "Added tag some-tag for changeset ad681a868e44"
  |
  o  2 ad681a868e44 (public) "add foo/file"
  |
  o  1 cbba8ecc03b7 (public) "remove foo"
  |
  o  0 327daa9251fa (public) "add foo and bar"
  

  $ hg out ../orig
  comparing with ../orig
  searching for changes
  no changes found
  [1]

dirstate should be empty:

  $ hg debugstate
  $ hg parents -q
  $ hg up -C
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg copy bar baz

put something in the dirstate:

  $ hg debugstate > debugstate
  $ grep baz debugstate
  a   0         -1 unset               baz
  copy: bar -> baz

add a new revision in the original repo

  $ cd ../orig
  $ echo baz > baz
  $ hg ci -qAm 'add baz'
  $ cd ..
  $ hg convert orig new 2>&1 | grep -v 'subversion python bindings could not be loaded'
  scanning source...
  sorting...
  converting...
  0 add baz
  $ cd new
  $ hg out ../orig
  comparing with ../orig
  searching for changes
  no changes found
  [1]

dirstate should be the same (no output below):

  $ hg debugstate > new-debugstate
  $ diff debugstate new-debugstate

no copies

  $ hg up -C
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg debugrename baz
  baz not renamed
  $ cd ..

test tag rewriting

  $ cat > filemap <<EOF
  > exclude foo
  > EOF
  $ hg convert --filemap filemap orig new-filemap 2>&1 | grep -v 'subversion python bindings could not be loaded'
  initializing destination new-filemap repository
  scanning source...
  sorting...
  converting...
  5 add foo and bar
  4 remove foo
  3 add foo/file
  2 Added tag some-tag for changeset ad681a868e44
  1 add a missing tag
  missing tag entry: "1234567890123456789012345678901234567890 missing_tag"
  0 add baz
  $ cd new-filemap
  $ hg tags
  tip                                3:7bb553f2c68a
  some-tag                           0:ba8636729451
  $ cd ..


Test cases for hg-hg roundtrip

Helper

  $ glog()
  > {
  >     hg log -G --template '{rev} {node|short} ({phase}) "{desc}" files: {files}\n' $*
  > }

Create a tricky source repo

  $ hg init source
  $ cd source

  $ echo 0 > 0
  $ hg ci -Aqm '0: add 0'
  $ echo a > a
  $ mkdir dir
  $ echo b > dir/b
  $ hg ci -qAm '1: add a and dir/b'
  $ echo c > dir/c
  $ hg ci -qAm '2: add dir/c'
  $ hg copy a e
  $ echo b >> b
  $ hg ci -qAm '3: copy a to e, change b'
  $ hg up -qr -3
  $ echo a >> a
  $ hg ci -qAm '4: change a'
  $ hg merge
  merging a and e to e
  2 files updated, 1 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg copy b dir/d
  $ hg ci -qAm '5: merge 2 and 3, copy b to dir/d'
  $ echo a >> a
  $ hg ci -qAm '6: change a'

  $ hg mani
  0
  a
  b
  dir/b
  dir/c
  dir/d
  e
  $ hg phase --public -r tip
  $ glog
  @  6 0613c8e59a3d (public) "6: change a" files: a
  |
  o    5 717e9b37cdb7 (public) "5: merge 2 and 3, copy b to dir/d" files: dir/d e
  |\
  | o  4 86a55cb968d5 (public) "4: change a" files: a
  | |
  o |  3 0e6e235919dd (public) "3: copy a to e, change b" files: b e
  | |
  o |  2 0394b0d5e4f7 (public) "2: add dir/c" files: dir/c
  |/
  o  1 333546584845 (public) "1: add a and dir/b" files: a dir/b
  |
  o  0 d1a24e2ebd23 (public) "0: add 0" files: 0
  
  $ cd ..

Convert excluding rev 0 and dir/ (and thus rev2):

  $ cat << EOF > filemap
  > exclude dir
  > EOF

  $ hg convert --filemap filemap source dest --config convert.hg.revs=1::
  initializing destination dest repository
  scanning source...
  sorting...
  converting...
  5 1: add a and dir/b
  4 2: add dir/c
  3 3: copy a to e, change b
  2 4: change a
  1 5: merge 2 and 3, copy b to dir/d
  0 6: change a

Verify that conversion skipped rev 2:

  $ glog -R dest
  o  4 78814e84a217 (draft) "6: change a" files: a
  |
  o    3 f7cff662c5e5 (draft) "5: merge 2 and 3, copy b to dir/d" files: e
  |\
  | o  2 ab40a95b0072 (draft) "4: change a" files: a
  | |
  o |  1 bd51f17597bf (draft) "3: copy a to e, change b" files: b e
  |/
  o  0 a4a1dae0fe35 (draft) "1: add a and dir/b" files: 0 a
  

Verify mapping correct in both directions:

  $ cat source/.hg/shamap
  a4a1dae0fe3514cefd9b8541b7abbc8f44f946d5 333546584845f70c4cfecb992341aaef0e708166
  bd51f17597bf32268e68a560b206898c3960cda2 0e6e235919dd8e9285ba8eb5adf703af9ad99378
  ab40a95b00725307e79c2fd271000aa8af9759f4 86a55cb968d51770cba2a1630d6cc637b574580a
  f7cff662c5e581e6f3f1a85ffdd2bcb35825f6ba 717e9b37cdb7eb9917ca8e30aa3f986e6d5b177d
  78814e84a217894517c2de392b903ed05e6871a4 0613c8e59a3ddb9789072ef52f1ed13496489bb4
  $ cat dest/.hg/shamap
  333546584845f70c4cfecb992341aaef0e708166 a4a1dae0fe3514cefd9b8541b7abbc8f44f946d5
  0394b0d5e4f761ced559fd0bbdc6afc16cb3f7d1 a4a1dae0fe3514cefd9b8541b7abbc8f44f946d5
  0e6e235919dd8e9285ba8eb5adf703af9ad99378 bd51f17597bf32268e68a560b206898c3960cda2
  86a55cb968d51770cba2a1630d6cc637b574580a ab40a95b00725307e79c2fd271000aa8af9759f4
  717e9b37cdb7eb9917ca8e30aa3f986e6d5b177d f7cff662c5e581e6f3f1a85ffdd2bcb35825f6ba
  0613c8e59a3ddb9789072ef52f1ed13496489bb4 78814e84a217894517c2de392b903ed05e6871a4

Verify meta data converted correctly:

  $ hg -R dest log -r 1 --debug -p --git
  changeset:   1:bd51f17597bf32268e68a560b206898c3960cda2
  phase:       draft
  parent:      0:a4a1dae0fe3514cefd9b8541b7abbc8f44f946d5
  parent:      -1:0000000000000000000000000000000000000000
  manifest:    1:040c72ed9b101773c24ac314776bfc846943781f
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files+:      b e
  extra:       branch=default
  description:
  3: copy a to e, change b
  
  
  diff --git a/b b/b
  new file mode 100644
  --- /dev/null
  +++ b/b
  @@ -0,0 +1,1 @@
  +b
  diff --git a/a b/e
  copy from a
  copy to e
  
Verify files included and excluded correctly:

  $ hg -R dest manifest -r tip
  0
  a
  b
  e


Make changes in dest and convert back:

  $ hg -R dest up -q
  $ echo dest > dest/dest
  $ hg -R dest ci -Aqm 'change in dest'
  $ hg -R dest tip
  changeset:   5:a2e0e3cc6d1d
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     change in dest
  

(converting merges back after using a filemap will probably cause chaos so we
exclude merges.)

  $ hg convert dest source --config convert.hg.revs='!merge()'
  scanning source...
  sorting...
  converting...
  0 change in dest

Verify the conversion back:

  $ hg -R source log --debug -r tip
  changeset:   7:e6d364a69ff1248b2099e603b0c145504cade6f0
  tag:         tip
  phase:       draft
  parent:      6:0613c8e59a3ddb9789072ef52f1ed13496489bb4
  parent:      -1:0000000000000000000000000000000000000000
  manifest:    7:aa3e9542f3b76d4f1f1b2e9c7ce9dbb48b6a95ec
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files+:      dest
  extra:       branch=default
  description:
  change in dest
  
  
Files that had been excluded are still present:

  $ hg -R source manifest -r tip
  0
  a
  b
  dest
  dir/b
  dir/c
  dir/d
  e

More source changes

  $ cd source
  $ echo 1 >> a
  $ hg ci -m '8: source first branch'
  created new head
  $ hg up -qr -2
  $ echo 2 >> a
  $ hg ci -m '9: source second branch'
  $ hg merge -q --tool internal:local
  $ hg ci -m '10: source merge'
  $ echo >> a
  $ hg ci -m '11: source change'

  $ hg mani
  0
  a
  b
  dest
  dir/b
  dir/c
  dir/d
  e

  $ glog -r 6:
  @  11 0c8927d1f7f4 (draft) "11: source change" files: a
  |
  o    10 9ccb7ee8d261 (draft) "10: source merge" files: a
  |\
  | o  9 f131b1518dba (draft) "9: source second branch" files: a
  | |
  o |  8 669cf0e74b50 (draft) "8: source first branch" files: a
  | |
  | o  7 e6d364a69ff1 (draft) "change in dest" files: dest
  |/
  o  6 0613c8e59a3d (public) "6: change a" files: a
  |
  ~
  $ cd ..

  $ hg convert --filemap filemap source dest --config convert.hg.revs=3:
  scanning source...
  sorting...
  converting...
  3 8: source first branch
  2 9: source second branch
  1 10: source merge
  0 11: source change

  $ glog -R dest
  o  9 8432d597b263 (draft) "11: source change" files: a
  |
  o    8 632ffacdcd6f (draft) "10: source merge" files: a
  |\
  | o  7 049cfee90ee6 (draft) "9: source second branch" files: a
  | |
  o |  6 9b6845e036e5 (draft) "8: source first branch" files: a
  | |
  | @  5 a2e0e3cc6d1d (draft) "change in dest" files: dest
  |/
  o  4 78814e84a217 (draft) "6: change a" files: a
  |
  o    3 f7cff662c5e5 (draft) "5: merge 2 and 3, copy b to dir/d" files: e
  |\
  | o  2 ab40a95b0072 (draft) "4: change a" files: a
  | |
  o |  1 bd51f17597bf (draft) "3: copy a to e, change b" files: b e
  |/
  o  0 a4a1dae0fe35 (draft) "1: add a and dir/b" files: 0 a
  
  $ cd ..

Two way tests

  $ hg init 0
  $ echo f > 0/f
  $ echo a > 0/a-only
  $ echo b > 0/b-only
  $ hg -R 0 ci -Aqm0

  $ cat << EOF > filemap-a
  > exclude b-only
  > EOF
  $ cat << EOF > filemap-b
  > exclude a-only
  > EOF
  $ hg convert --filemap filemap-a 0 a
  initializing destination a repository
  scanning source...
  sorting...
  converting...
  0 0
  $ hg -R a up -q
  $ echo a > a/f
  $ hg -R a ci -ma

  $ hg convert --filemap filemap-b 0 b
  initializing destination b repository
  scanning source...
  sorting...
  converting...
  0 0
  $ hg -R b up -q
  $ echo b > b/f
  $ hg -R b ci -mb

  $ tail 0/.hg/shamap
  86f3f774ffb682bffb5dc3c1d3b3da637cb9a0d6 8a028c7c77f6c7bd6d63bc3f02ca9f779eabf16a
  dd9f218eb91fb857f2a62fe023e1d64a4e7812fe 8a028c7c77f6c7bd6d63bc3f02ca9f779eabf16a
  $ tail a/.hg/shamap
  8a028c7c77f6c7bd6d63bc3f02ca9f779eabf16a 86f3f774ffb682bffb5dc3c1d3b3da637cb9a0d6
  $ tail b/.hg/shamap
  8a028c7c77f6c7bd6d63bc3f02ca9f779eabf16a dd9f218eb91fb857f2a62fe023e1d64a4e7812fe

  $ hg convert a 0
  scanning source...
  sorting...
  converting...
  0 a

  $ hg convert b 0
  scanning source...
  sorting...
  converting...
  0 b

  $ hg -R 0 log -G
  o  changeset:   2:637fbbbe96b6
  |  tag:         tip
  |  parent:      0:8a028c7c77f6
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     b
  |
  | o  changeset:   1:ec7b9c96e692
  |/   user:        test
  |    date:        Thu Jan 01 00:00:00 1970 +0000
  |    summary:     a
  |
  @  changeset:   0:8a028c7c77f6
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     0
  
  $ hg convert --filemap filemap-b 0 a --config convert.hg.revs=1::
  scanning source...
  sorting...
  converting...

  $ hg -R 0 up -r1
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo f >> 0/f
  $ hg -R 0 ci -mx

  $ hg convert --filemap filemap-b 0 a --config convert.hg.revs=1::
  scanning source...
  sorting...
  converting...
  0 x

  $ hg -R a log -G -T '{rev} {desc|firstline} ({files})\n'
  o  2 x (f)
  |
  @  1 a (f)
  |
  o  0 0 (a-only f)
  
  $ hg -R a mani -r tip
  a-only
  f

An additional round, demonstrating that unchanged files don't get converted

  $ echo f >> 0/f
  $ echo f >> 0/a-only
  $ hg -R 0 ci -m "extra f+a-only change"

  $ hg convert --filemap filemap-b 0 a --config convert.hg.revs=1::
  scanning source...
  sorting...
  converting...
  0 extra f+a-only change

  $ hg -R a log -G -T '{rev} {desc|firstline} ({files})\n'
  o  3 extra f+a-only change (f)
  |
  o  2 x (f)
  |
  @  1 a (f)
  |
  o  0 0 (a-only f)
  

Conversion after rollback

  $ hg -R a rollback -f
  repository tip rolled back to revision 2 (undo convert)

  $ hg convert --filemap filemap-b 0 a --config convert.hg.revs=1::
  scanning source...
  sorting...
  converting...
  0 extra f+a-only change

  $ hg -R a log -G -T '{rev} {desc|firstline} ({files})\n'
  o  3 extra f+a-only change (f)
  |
  o  2 x (f)
  |
  @  1 a (f)
  |
  o  0 0 (a-only f)
  
Convert with --full adds and removes files that didn't change

  $ echo f >> 0/f
  $ hg -R 0 ci -m "f"
  $ hg convert --filemap filemap-b --full 0 a --config convert.hg.revs=1::
  scanning source...
  sorting...
  converting...
  0 f
  $ hg -R a status --change tip
  M f
  A b-only
  R a-only