view tests/test-obsmarkers-effectflag.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

Test the 'effect-flags' feature

Global setup
============

  $ . $TESTDIR/testlib/obsmarker-common.sh
  $ cat >> $HGRCPATH <<EOF
  > [ui]
  > interactive = true
  > [phases]
  > publish=False
  > [extensions]
  > rebase =
  > [experimental]
  > evolution = all
  > evolution.effect-flags = 1
  > EOF

  $ hg init $TESTTMP/effect-flags
  $ cd $TESTTMP/effect-flags
  $ mkcommit ROOT

amend touching the description only
-----------------------------------

  $ mkcommit A0
  $ hg commit --amend -m "A1"

check result

  $ hg debugobsolete --rev .
  471f378eab4c5e25f6c77f785b27c936efb22874 fdf9bde5129a28d4548fadd3f62b265cdd3b7a2e 0 (Thu Jan 01 00:00:00 1970 +0000) {'ef1': '1', 'operation': 'amend', 'user': 'test'}

amend touching the user only
----------------------------

  $ mkcommit B0
  $ hg commit --amend -u "bob <[e-mail]>"

check result

  $ hg debugobsolete --rev .
  ef4a313b1e0ade55718395d80e6b88c5ccd875eb 5485c92d34330dac9d7a63dc07e1e3373835b964 0 (Thu Jan 01 00:00:00 1970 +0000) {'ef1': '16', 'operation': 'amend', 'user': 'test'}

amend touching the date only
----------------------------

  $ mkcommit B1
  $ hg commit --amend -d "42 0"

check result

  $ hg debugobsolete --rev .
  2ef0680ff45038ac28c9f1ff3644341f54487280 4dd84345082e9e5291c2e6b3f335bbf8bf389378 0 (Thu Jan 01 00:00:00 1970 +0000) {'ef1': '32', 'operation': 'amend', 'user': 'test'}

amend touching the branch only
----------------------------

  $ mkcommit B2
  $ hg branch my-branch
  marked working directory as branch my-branch
  (branches are permanent and global, did you want a bookmark?)
  $ hg commit --amend

check result

  $ hg debugobsolete --rev .
  bd3db8264ceebf1966319f5df3be7aac6acd1a8e 14a01456e0574f0e0a0b15b2345486a6364a8d79 0 (Thu Jan 01 00:00:00 1970 +0000) {'ef1': '64', 'operation': 'amend', 'user': 'test'}

  $ hg up default
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

rebase (parents change)
-----------------------

  $ mkcommit C0
  $ mkcommit D0
  $ hg rebase -r . -d 'desc(B0)'
  rebasing 10:c85eff83a034 "D0" (tip)

check result

  $ hg debugobsolete --rev .
  c85eff83a0340efd9da52b806a94c350222f3371 da86aa2f19a30d6686b15cae15c7b6c908ec9699 0 (Thu Jan 01 00:00:00 1970 +0000) {'ef1': '4', 'operation': 'rebase', 'user': 'test'}

amend touching the diff
-----------------------

  $ mkcommit E0
  $ echo 42 >> E0
  $ hg commit --amend

check result

  $ hg debugobsolete --rev .
  ebfe0333e0d96f68a917afd97c0a0af87f1c3b5f 75781fdbdbf58a987516b00c980bccda1e9ae588 0 (Thu Jan 01 00:00:00 1970 +0000) {'ef1': '8', 'operation': 'amend', 'user': 'test'}

amend with multiple effect (desc and meta)
-------------------------------------------

  $ mkcommit F0
  $ hg branch my-other-branch
  marked working directory as branch my-other-branch
  $ hg commit --amend -m F1 -u "bob <[e-mail]>" -d "42 0"

check result

  $ hg debugobsolete --rev .
  fad47e5bd78e6aa4db1b5a0a1751bc12563655ff a94e0fd5f1c81d969381a76eb0d37ce499a44fae 0 (Thu Jan 01 00:00:00 1970 +0000) {'ef1': '113', 'operation': 'amend', 'user': 'test'}

rebase not touching the diff
----------------------------

  $ cat << EOF > H0
  > 0
  > 1
  > 2
  > 3
  > 4
  > 5
  > 6
  > 7
  > 8
  > 9
  > 10
  > EOF
  $ hg add H0
  $ hg commit -m 'H0'
  $ echo "H1" >> H0
  $ hg commit -m "H1"
  $ hg up -r "desc(H0)"
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cat << EOF > H0
  > H2
  > 0
  > 1
  > 2
  > 3
  > 4
  > 5
  > 6
  > 7
  > 8
  > 9
  > 10
  > EOF
  $ hg commit -m "H2"
  created new head
  $ hg rebase -s "desc(H1)" -d "desc(H2)" -t :merge3
  rebasing 17:b57fed8d8322 "H1"
  merging H0
  $ hg debugobsolete -r tip
  b57fed8d83228a8ae3748d8c3760a77638dd4f8c e509e2eb3df5d131ff7c02350bf2a9edd0c09478 0 (Thu Jan 01 00:00:00 1970 +0000) {'ef1': '4', 'operation': 'rebase', 'user': 'test'}

amend closing the branch should be detected as meta change
----------------------------------------------------------

  $ hg branch closedbranch
  marked working directory as branch closedbranch
  $ mkcommit G0
  $ mkcommit I0
  $ hg commit --amend --close-branch

check result

  $ hg debugobsolete -r .
  2f599e54c1c6974299065cdf54e1ad640bfb7b5d 12c6238b5e371eea00fd2013b12edce3f070928b 0 (Thu Jan 01 00:00:00 1970 +0000) {'ef1': '2', 'operation': 'amend', 'user': 'test'}