Mercurial > hg
view tests/test-obsolete-changeset-exchange.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
author | Gregory Szorc <gregory.szorc@gmail.com> |
---|---|
date | Wed, 26 Sep 2018 17:16:56 -0700 |
parents | f9232b0310ef |
children | 34a46d48d24e |
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Test changesets filtering during exchanges (some tests are still in test-obsolete.t) $ cat >> $HGRCPATH << EOF > [experimental] > evolution.createmarkers=True > EOF Push does not corrupt remote ---------------------------- Create a DAG where a changeset reuses a revision from a file first used in an extinct changeset. $ hg init local $ cd local $ echo 'base' > base $ hg commit -Am base adding base $ echo 'A' > A $ hg commit -Am A adding A $ hg up 0 0 files updated, 0 files merged, 1 files removed, 0 files unresolved $ hg revert -ar 1 adding A $ hg commit -Am "A'" created new head $ hg log -G --template='{desc} {node}' @ A' f89bcc95eba5174b1ccc3e33a82e84c96e8338ee | | o A 9d73aac1b2ed7d53835eaeec212ed41ea47da53a |/ o base d20a80d4def38df63a4b330b7fb688f3d4cae1e3 $ hg debugobsolete 9d73aac1b2ed7d53835eaeec212ed41ea47da53a f89bcc95eba5174b1ccc3e33a82e84c96e8338ee obsoleted 1 changesets Push it. The bundle should not refer to the extinct changeset. $ hg init ../other $ hg push ../other pushing to ../other searching for changes adding changesets adding manifests adding file changes added 2 changesets with 2 changes to 2 files $ hg -R ../other verify checking changesets checking manifests crosschecking files in changesets and manifests checking files checked 2 changesets with 2 changes to 2 files Adding a changeset going extinct locally ------------------------------------------ Pull a changeset that will immediatly goes extinct (because you already have a marker to obsolete him) (test resolution of issue3788) $ hg phase --draft --force f89bcc95eba5 $ hg phase -R ../other --draft --force f89bcc95eba5 $ hg commit --amend -m "A''" $ hg --hidden --config extensions.mq= strip --no-backup f89bcc95eba5 $ hg pull ../other pulling from ../other searching for changes adding changesets adding manifests adding file changes added 1 changesets with 0 changes to 1 files (+1 heads) 1 new phase-divergent changesets new changesets f89bcc95eba5 (run 'hg heads' to see heads, 'hg merge' to merge) check that bundle is not affected $ hg bundle --hidden --rev f89bcc95eba5 --base "f89bcc95eba5^" ../f89bcc95eba5.hg 1 changesets found $ hg --hidden --config extensions.mq= strip --no-backup f89bcc95eba5 $ hg unbundle ../f89bcc95eba5.hg adding changesets adding manifests adding file changes added 1 changesets with 0 changes to 1 files (+1 heads) (1 other changesets obsolete on arrival) (run 'hg heads' to see heads) check-that bundle can contain markers: $ hg bundle --hidden --rev f89bcc95eba5 --base "f89bcc95eba5^" ../f89bcc95eba5-obs.hg --config experimental.evolution.bundle-obsmarker=1 1 changesets found $ hg debugbundle ../f89bcc95eba5.hg Stream params: {Compression: BZ} changegroup -- {nbchanges: 1, version: 02} (mandatory: True) f89bcc95eba5174b1ccc3e33a82e84c96e8338ee cache:rev-branch-cache -- {} (mandatory: False) $ hg debugbundle ../f89bcc95eba5-obs.hg Stream params: {Compression: BZ} changegroup -- {nbchanges: 1, version: 02} (mandatory: True) f89bcc95eba5174b1ccc3e33a82e84c96e8338ee cache:rev-branch-cache -- {} (mandatory: False) obsmarkers -- {} (mandatory: True) version: 1 (70 bytes) 9d73aac1b2ed7d53835eaeec212ed41ea47da53a f89bcc95eba5174b1ccc3e33a82e84c96e8338ee 0 (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'} $ cd .. pull does not fetch excessive changesets when common node is hidden (issue4982) ------------------------------------------------------------------------------- initial repo with server and client matching $ hg init pull-hidden-common $ cd pull-hidden-common $ touch foo $ hg -q commit -A -m initial $ echo 1 > foo $ hg commit -m 1 $ echo 2a > foo $ hg commit -m 2a $ cd .. $ hg clone --pull pull-hidden-common pull-hidden-common-client requesting all changes adding changesets adding manifests adding file changes added 3 changesets with 3 changes to 1 files new changesets 96ee1d7354c4:6a29ed9c68de updating to branch default 1 files updated, 0 files merged, 0 files removed, 0 files unresolved server obsoletes the old head $ cd pull-hidden-common $ hg -q up -r 1 $ echo 2b > foo $ hg -q commit -m 2b $ hg debugobsolete 6a29ed9c68defff1a139e5c6fa9696fb1a75783d bec0734cd68e84477ba7fc1d13e6cff53ab70129 obsoleted 1 changesets $ cd .. client only pulls down 1 changeset $ cd pull-hidden-common-client $ hg pull --debug pulling from $TESTTMP/pull-hidden-common query 1; heads searching for changes taking quick initial sample query 2; still undecided: 2, sample size is: 2 2 total queries in *.????s (glob) 1 changesets found list of changesets: bec0734cd68e84477ba7fc1d13e6cff53ab70129 listing keys for "bookmarks" bundle2-output-bundle: "HG20", 4 parts total bundle2-output-part: "changegroup" (params: 1 mandatory 1 advisory) streamed payload bundle2-output-part: "listkeys" (params: 1 mandatory) empty payload bundle2-output-part: "phase-heads" 24 bytes payload bundle2-output-part: "cache:rev-branch-cache" (advisory) streamed payload bundle2-input-bundle: with-transaction bundle2-input-part: "changegroup" (params: 1 mandatory 1 advisory) supported adding changesets add changeset bec0734cd68e adding manifests adding file changes adding foo revisions added 1 changesets with 1 changes to 1 files (+1 heads) bundle2-input-part: total payload size 476 bundle2-input-part: "listkeys" (params: 1 mandatory) supported bundle2-input-part: "phase-heads" supported bundle2-input-part: total payload size 24 bundle2-input-part: "cache:rev-branch-cache" (advisory) supported bundle2-input-part: total payload size 39 bundle2-input-bundle: 3 parts total checking for updated bookmarks updating the branch cache new changesets bec0734cd68e (run 'hg heads' to see heads, 'hg merge' to merge)