view tests/test-rebase-parameters.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]
  > rebase=
  > 
  > [phases]
  > publish=False
  > 
  > [alias]
  > tglog = log -G --template "{rev}: {node|short} '{desc}' {branches}\n"
  > EOF


  $ hg init a
  $ cd a
  $ hg unbundle "$TESTDIR/bundles/rebase.hg"
  adding changesets
  adding manifests
  adding file changes
  added 8 changesets with 7 changes to 7 files (+2 heads)
  new changesets cd010b8cd998:02de42196ebe (8 drafts)
  (run 'hg heads' to see heads, 'hg merge' to merge)
  $ hg up tip
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ echo I > I
  $ hg ci -AmI
  adding I

  $ hg tglog
  @  8: e7ec4e813ba6 'I'
  |
  o  7: 02de42196ebe 'H'
  |
  | o  6: eea13746799a 'G'
  |/|
  o |  5: 24b6387c8c8c 'F'
  | |
  | o  4: 9520eea781bc 'E'
  |/
  | o  3: 32af7686d403 'D'
  | |
  | o  2: 5fddd98957c8 'C'
  | |
  | o  1: 42ccdea3bb16 'B'
  |/
  o  0: cd010b8cd998 'A'
  
  $ cd ..

Version with only two heads (to allow default destination to work)

  $ hg clone -q -u . a a2heads -r 3 -r 8

These fail:

  $ hg clone -q -u . a a0
  $ cd a0

  $ hg rebase -s 8 -d 7
  nothing to rebase
  [1]

  $ hg rebase --continue --abort
  abort: cannot use --abort with --continue
  [255]

  $ hg rebase --continue --collapse
  abort: cannot use collapse with continue or abort
  [255]

  $ hg rebase --continue --dest 4
  abort: abort and continue do not allow specifying revisions
  [255]

  $ hg rebase --base 5 --source 4
  abort: cannot specify both a source and a base
  [255]

  $ hg rebase --rev 5 --source 4
  abort: cannot specify both a revision and a source
  [255]
  $ hg rebase --base 5 --rev 4
  abort: cannot specify both a revision and a base
  [255]

  $ hg rebase --base 6
  abort: branch 'default' has 3 heads - please rebase to an explicit rev
  (run 'hg heads .' to see heads)
  [255]

  $ hg rebase --rev '1 & !1' --dest 8
  empty "rev" revision set - nothing to rebase
  [1]

  $ hg rebase --source '1 & !1' --dest 8
  empty "source" revision set - nothing to rebase
  [1]

  $ hg rebase --base '1 & !1' --dest 8
  empty "base" revision set - can't compute rebase set
  [1]

  $ hg rebase --dest 8
  nothing to rebase - working directory parent is also destination
  [1]

  $ hg rebase -b . --dest 8
  nothing to rebase - e7ec4e813ba6 is both "base" and destination
  [1]

  $ hg up -q 7

  $ hg rebase --dest 8 --traceback
  nothing to rebase - working directory parent is already an ancestor of destination e7ec4e813ba6
  [1]

  $ hg rebase --dest 8 -b.
  nothing to rebase - "base" 02de42196ebe is already an ancestor of destination e7ec4e813ba6
  [1]

  $ hg rebase --dest '1 & !1'
  abort: empty revision set
  [255]

These work:

Rebase with no arguments (from 3 onto 8):

  $ cd ..
  $ hg clone -q -u . a2heads a1
  $ cd a1
  $ hg up -q -C 3

  $ hg rebase
  rebasing 1:42ccdea3bb16 "B"
  rebasing 2:5fddd98957c8 "C"
  rebasing 3:32af7686d403 "D"
  saved backup bundle to $TESTTMP/a1/.hg/strip-backup/42ccdea3bb16-3cb021d3-rebase.hg

  $ hg tglog
  @  6: ed65089c18f8 'D'
  |
  o  5: 7621bf1a2f17 'C'
  |
  o  4: 9430a62369c6 'B'
  |
  o  3: e7ec4e813ba6 'I'
  |
  o  2: 02de42196ebe 'H'
  |
  o  1: 24b6387c8c8c 'F'
  |
  o  0: cd010b8cd998 'A'
  
Try to rollback after a rebase (fail):

  $ hg rollback
  no rollback information available
  [1]

  $ cd ..

Rebase with base == '.' => same as no arguments (from 3 onto 8):

  $ hg clone -q -u 3 a2heads a2
  $ cd a2

  $ hg rebase --base .
  rebasing 1:42ccdea3bb16 "B"
  rebasing 2:5fddd98957c8 "C"
  rebasing 3:32af7686d403 "D"
  saved backup bundle to $TESTTMP/a2/.hg/strip-backup/42ccdea3bb16-3cb021d3-rebase.hg

  $ hg tglog
  @  6: ed65089c18f8 'D'
  |
  o  5: 7621bf1a2f17 'C'
  |
  o  4: 9430a62369c6 'B'
  |
  o  3: e7ec4e813ba6 'I'
  |
  o  2: 02de42196ebe 'H'
  |
  o  1: 24b6387c8c8c 'F'
  |
  o  0: cd010b8cd998 'A'
  
  $ cd ..


Rebase with dest == branch(.) => same as no arguments (from 3 onto 8):

  $ hg clone -q -u 3 a a3
  $ cd a3

  $ hg rebase --dest 'branch(.)'
  rebasing 1:42ccdea3bb16 "B"
  rebasing 2:5fddd98957c8 "C"
  rebasing 3:32af7686d403 "D"
  saved backup bundle to $TESTTMP/a3/.hg/strip-backup/42ccdea3bb16-3cb021d3-rebase.hg

  $ hg tglog
  @  8: ed65089c18f8 'D'
  |
  o  7: 7621bf1a2f17 'C'
  |
  o  6: 9430a62369c6 'B'
  |
  o  5: e7ec4e813ba6 'I'
  |
  o  4: 02de42196ebe 'H'
  |
  | o  3: eea13746799a 'G'
  |/|
  o |  2: 24b6387c8c8c 'F'
  | |
  | o  1: 9520eea781bc 'E'
  |/
  o  0: cd010b8cd998 'A'
  
  $ cd ..


Specify only source (from 2 onto 8):

  $ hg clone -q -u . a2heads a4
  $ cd a4

  $ hg rebase --source 'desc("C")'
  rebasing 2:5fddd98957c8 "C"
  rebasing 3:32af7686d403 "D"
  saved backup bundle to $TESTTMP/a4/.hg/strip-backup/5fddd98957c8-f9244fa1-rebase.hg

  $ hg tglog
  o  6: 7726e9fd58f7 'D'
  |
  o  5: 72c8333623d0 'C'
  |
  @  4: e7ec4e813ba6 'I'
  |
  o  3: 02de42196ebe 'H'
  |
  o  2: 24b6387c8c8c 'F'
  |
  | o  1: 42ccdea3bb16 'B'
  |/
  o  0: cd010b8cd998 'A'
  
  $ cd ..


Specify only dest (from 3 onto 6):

  $ hg clone -q -u 3 a a5
  $ cd a5

  $ hg rebase --dest 6
  rebasing 1:42ccdea3bb16 "B"
  rebasing 2:5fddd98957c8 "C"
  rebasing 3:32af7686d403 "D"
  saved backup bundle to $TESTTMP/a5/.hg/strip-backup/42ccdea3bb16-3cb021d3-rebase.hg

  $ hg tglog
  @  8: 8eeb3c33ad33 'D'
  |
  o  7: 2327fea05063 'C'
  |
  o  6: e4e5be0395b2 'B'
  |
  | o  5: e7ec4e813ba6 'I'
  | |
  | o  4: 02de42196ebe 'H'
  | |
  o |  3: eea13746799a 'G'
  |\|
  | o  2: 24b6387c8c8c 'F'
  | |
  o |  1: 9520eea781bc 'E'
  |/
  o  0: cd010b8cd998 'A'
  
  $ cd ..


Specify only base (from 1 onto 8):

  $ hg clone -q -u . a2heads a6
  $ cd a6

  $ hg rebase --base 'desc("D")'
  rebasing 1:42ccdea3bb16 "B"
  rebasing 2:5fddd98957c8 "C"
  rebasing 3:32af7686d403 "D"
  saved backup bundle to $TESTTMP/a6/.hg/strip-backup/42ccdea3bb16-3cb021d3-rebase.hg

  $ hg tglog
  o  6: ed65089c18f8 'D'
  |
  o  5: 7621bf1a2f17 'C'
  |
  o  4: 9430a62369c6 'B'
  |
  @  3: e7ec4e813ba6 'I'
  |
  o  2: 02de42196ebe 'H'
  |
  o  1: 24b6387c8c8c 'F'
  |
  o  0: cd010b8cd998 'A'
  
  $ cd ..


Specify source and dest (from 2 onto 7):

  $ hg clone -q -u . a a7
  $ cd a7

  $ hg rebase --source 2 --dest 7
  rebasing 2:5fddd98957c8 "C"
  rebasing 3:32af7686d403 "D"
  saved backup bundle to $TESTTMP/a7/.hg/strip-backup/5fddd98957c8-f9244fa1-rebase.hg

  $ hg tglog
  o  8: 668acadedd30 'D'
  |
  o  7: 09eb682ba906 'C'
  |
  | @  6: e7ec4e813ba6 'I'
  |/
  o  5: 02de42196ebe 'H'
  |
  | o  4: eea13746799a 'G'
  |/|
  o |  3: 24b6387c8c8c 'F'
  | |
  | o  2: 9520eea781bc 'E'
  |/
  | o  1: 42ccdea3bb16 'B'
  |/
  o  0: cd010b8cd998 'A'
  
  $ cd ..


Specify base and dest (from 1 onto 7):

  $ hg clone -q -u . a a8
  $ cd a8

  $ hg rebase --base 3 --dest 7
  rebasing 1:42ccdea3bb16 "B"
  rebasing 2:5fddd98957c8 "C"
  rebasing 3:32af7686d403 "D"
  saved backup bundle to $TESTTMP/a8/.hg/strip-backup/42ccdea3bb16-3cb021d3-rebase.hg

  $ hg tglog
  o  8: 287cc92ba5a4 'D'
  |
  o  7: 6824f610a250 'C'
  |
  o  6: 7c6027df6a99 'B'
  |
  | @  5: e7ec4e813ba6 'I'
  |/
  o  4: 02de42196ebe 'H'
  |
  | o  3: eea13746799a 'G'
  |/|
  o |  2: 24b6387c8c8c 'F'
  | |
  | o  1: 9520eea781bc 'E'
  |/
  o  0: cd010b8cd998 'A'
  
  $ cd ..


Specify only revs (from 2 onto 8)

  $ hg clone -q -u . a2heads a9
  $ cd a9

  $ hg rebase --rev 'desc("C")::'
  rebasing 2:5fddd98957c8 "C"
  rebasing 3:32af7686d403 "D"
  saved backup bundle to $TESTTMP/a9/.hg/strip-backup/5fddd98957c8-f9244fa1-rebase.hg

  $ hg tglog
  o  6: 7726e9fd58f7 'D'
  |
  o  5: 72c8333623d0 'C'
  |
  @  4: e7ec4e813ba6 'I'
  |
  o  3: 02de42196ebe 'H'
  |
  o  2: 24b6387c8c8c 'F'
  |
  | o  1: 42ccdea3bb16 'B'
  |/
  o  0: cd010b8cd998 'A'
  
  $ cd ..

Rebasing both a single revision and a merge in one command

  $ hg clone -q -u . a aX
  $ cd aX
  $ hg rebase -r 3 -r 6 --dest 8
  rebasing 3:32af7686d403 "D"
  rebasing 6:eea13746799a "G"
  saved backup bundle to $TESTTMP/aX/.hg/strip-backup/eea13746799a-ad273fd6-rebase.hg
  $ cd ..

Test --tool parameter:

  $ hg init b
  $ cd b

  $ echo c1 > c1
  $ hg ci -Am c1
  adding c1

  $ echo c2 > c2
  $ hg ci -Am c2
  adding c2

  $ hg up -q 0
  $ echo c2b > c2
  $ hg ci -Am c2b
  adding c2
  created new head

  $ cd ..

  $ hg clone -q -u . b b1
  $ cd b1

  $ hg rebase -s 2 -d 1 --tool internal:local
  rebasing 2:e4e3f3546619 "c2b" (tip)
  note: rebase of 2:e4e3f3546619 created no changes to commit
  saved backup bundle to $TESTTMP/b1/.hg/strip-backup/e4e3f3546619-b0841178-rebase.hg

  $ hg cat c2
  c2

  $ cd ..


  $ hg clone -q -u . b b2
  $ cd b2

  $ hg rebase -s 2 -d 1 --tool internal:other
  rebasing 2:e4e3f3546619 "c2b" (tip)
  saved backup bundle to $TESTTMP/b2/.hg/strip-backup/e4e3f3546619-b0841178-rebase.hg

  $ hg cat c2
  c2b

  $ cd ..


  $ hg clone -q -u . b b3
  $ cd b3

  $ hg rebase -s 2 -d 1 --tool internal:fail
  rebasing 2:e4e3f3546619 "c2b" (tip)
  unresolved conflicts (see hg resolve, then hg rebase --continue)
  [1]

  $ hg summary
  parent: 1:56daeba07f4b 
   c2
  parent: 2:e4e3f3546619 tip
   c2b
  branch: default
  commit: 1 modified, 1 unresolved (merge)
  update: (current)
  phases: 3 draft
  rebase: 0 rebased, 1 remaining (rebase --continue)

  $ hg resolve -l
  U c2

  $ hg resolve -m c2
  (no more unresolved files)
  continue: hg rebase --continue
  $ hg graft --continue
  abort: no graft in progress
  (continue: hg rebase --continue)
  [255]
  $ hg rebase -c --tool internal:fail
  rebasing 2:e4e3f3546619 "c2b" (tip)
  note: rebase of 2:e4e3f3546619 created no changes to commit
  saved backup bundle to $TESTTMP/b3/.hg/strip-backup/e4e3f3546619-b0841178-rebase.hg

  $ hg rebase -i
  abort: interactive history editing is supported by the 'histedit' extension (see "hg --config extensions.histedit= help -e histedit")
  [255]

  $ hg rebase --interactive
  abort: interactive history editing is supported by the 'histedit' extension (see "hg --config extensions.histedit= help -e histedit")
  [255]

  $ cd ..

No common ancestor

  $ hg init separaterepo
  $ cd separaterepo
  $ touch a
  $ hg commit -Aqm a
  $ hg up -q null
  $ touch b
  $ hg commit -Aqm b
  $ hg rebase -d 0
  nothing to rebase from d7486e00c6f1 to 3903775176ed
  [1]
  $ cd ..