view tests/test-contrib-perf.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

#require test-repo

Set vars:

  $ . "$TESTDIR/helpers-testrepo.sh"
  $ CONTRIBDIR="$TESTDIR/../contrib"

Prepare repo:

  $ hg init

  $ echo this is file a > a
  $ hg add a
  $ hg commit -m first

  $ echo adding to file a >> a
  $ hg commit -m second

  $ echo adding more to file a >> a
  $ hg commit -m third

  $ hg up -r 0
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo merge-this >> a
  $ hg commit -m merge-able
  created new head

  $ hg up -r 2
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

perfstatus

  $ cat >> $HGRCPATH << EOF
  > [extensions]
  > perfstatusext=$CONTRIBDIR/perf.py
  > [perf]
  > presleep=0
  > stub=on
  > parentscount=1
  > EOF
  $ hg help perfstatusext
  perfstatusext extension - helper extension to measure performance
  
  list of commands:
  
   perfaddremove
                 (no help text available)
   perfancestors
                 (no help text available)
   perfancestorset
                 (no help text available)
   perfannotate  (no help text available)
   perfbdiff     benchmark a bdiff between revisions
   perfbookmarks
                 benchmark parsing bookmarks from disk to memory
   perfbranchmap
                 benchmark the update of a branchmap
   perfbranchmapload
                 benchmark reading the branchmap
   perfbundleread
                 Benchmark reading of bundle files.
   perfcca       (no help text available)
   perfchangegroupchangelog
                 Benchmark producing a changelog group for a changegroup.
   perfchangeset
                 (no help text available)
   perfctxfiles  (no help text available)
   perfdiffwd    Profile diff of working directory changes
   perfdirfoldmap
                 (no help text available)
   perfdirs      (no help text available)
   perfdirstate  (no help text available)
   perfdirstatedirs
                 (no help text available)
   perfdirstatefoldmap
                 (no help text available)
   perfdirstatewrite
                 (no help text available)
   perffncacheencode
                 (no help text available)
   perffncacheload
                 (no help text available)
   perffncachewrite
                 (no help text available)
   perfheads     (no help text available)
   perfindex     (no help text available)
   perflinelogedits
                 (no help text available)
   perfloadmarkers
                 benchmark the time to parse the on-disk markers for a repo
   perflog       (no help text available)
   perflookup    (no help text available)
   perflrucachedict
                 (no help text available)
   perfmanifest  benchmark the time to read a manifest from disk and return a
                 usable
   perfmergecalculate
                 (no help text available)
   perfmoonwalk  benchmark walking the changelog backwards
   perfnodelookup
                 (no help text available)
   perfparents   (no help text available)
   perfpathcopies
                 (no help text available)
   perfphases    benchmark phasesets computation
   perfphasesremote
                 benchmark time needed to analyse phases of the remote server
   perfrawfiles  (no help text available)
   perfrevlogchunks
                 Benchmark operations on revlog chunks.
   perfrevlogindex
                 Benchmark operations against a revlog index.
   perfrevlogrevision
                 Benchmark obtaining a revlog revision.
   perfrevlogrevisions
                 Benchmark reading a series of revisions from a revlog.
   perfrevrange  (no help text available)
   perfrevset    benchmark the execution time of a revset
   perfstartup   (no help text available)
   perfstatus    (no help text available)
   perftags      (no help text available)
   perftemplating
                 test the rendering time of a given template
   perfunidiff   benchmark a unified diff between revisions
   perfvolatilesets
                 benchmark the computation of various volatile set
   perfwalk      (no help text available)
   perfwrite     microbenchmark ui.write
  
  (use 'hg help -v perfstatusext' to show built-in aliases and global options)
  $ hg perfaddremove
  $ hg perfancestors
  $ hg perfancestorset 2
  $ hg perfannotate a
  $ hg perfbdiff -c 1
  $ hg perfbdiff --alldata 1
  $ hg perfunidiff -c 1
  $ hg perfunidiff --alldata 1
  $ hg perfbookmarks
  $ hg perfbranchmap
  $ hg perfcca
  $ hg perfchangegroupchangelog
  $ hg perfchangeset 2
  $ hg perfctxfiles 2
  $ hg perfdiffwd
  $ hg perfdirfoldmap
  $ hg perfdirs
  $ hg perfdirstate
  $ hg perfdirstatedirs
  $ hg perfdirstatefoldmap
  $ hg perfdirstatewrite
#if repofncache
  $ hg perffncacheencode
  $ hg perffncacheload
  $ hg debugrebuildfncache
  fncache already up to date
  $ hg perffncachewrite
  $ hg debugrebuildfncache
  fncache already up to date
#endif
  $ hg perfheads
  $ hg perfindex
  $ hg perflinelogedits -n 1
  $ hg perfloadmarkers
  $ hg perflog
  $ hg perflookup 2
  $ hg perflrucache
  $ hg perfmanifest 2
  $ hg perfmanifest -m 44fe2c8352bb3a478ffd7d8350bbc721920134d1
  $ hg perfmanifest -m 44fe2c8352bb
  abort: manifest revision must be integer or full node
  [255]
  $ hg perfmergecalculate -r 3
  $ hg perfmoonwalk
  $ hg perfnodelookup 2
  $ hg perfpathcopies 1 2
  $ hg perfrawfiles 2
  $ hg perfrevlogindex -c
#if reporevlogstore
  $ hg perfrevlogrevisions .hg/store/data/a.i
#endif
  $ hg perfrevlogrevision -m 0
  $ hg perfrevlogchunks -c
  $ hg perfrevrange
  $ hg perfrevset 'all()'
  $ hg perfstartup
  $ hg perfstatus
  $ hg perftags
  $ hg perftemplating
  $ hg perfvolatilesets
  $ hg perfwalk
  $ hg perfparents

test actual output
------------------

normal output:

  $ hg perfheads --config perf.stub=no
  ! wall * comb * user * sys * (best of *) (glob)

detailed output:

  $ hg perfheads --config perf.all-timing=yes --config perf.stub=no
  ! wall * comb * user * sys * (best of *) (glob)
  ! wall * comb * user * sys * (max of *) (glob)
  ! wall * comb * user * sys * (avg of *) (glob)
  ! wall * comb * user * sys * (median of *) (glob)

Check perf.py for historical portability
----------------------------------------

  $ cd "$TESTDIR/.."

  $ (testrepohg files -r 1.2 glob:mercurial/*.c glob:mercurial/*.py;
  >  testrepohg files -r tip glob:mercurial/*.c glob:mercurial/*.py) |
  > "$TESTDIR"/check-perf-code.py contrib/perf.py
  contrib/perf.py:\d+: (re)
   >     from mercurial import (
   import newer module separately in try clause for early Mercurial
  contrib/perf.py:\d+: (re)
   >     from mercurial import (
   import newer module separately in try clause for early Mercurial
  [1]