Mercurial > hg
annotate tests/test-merge-revert2.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 | ce3a133f71b3 |
children | 55c6ebd11cb9 |
rev | line source |
---|---|
12279 | 1 $ hg init |
2 | |
3 $ echo "added file1" > file1 | |
4 $ echo "another line of text" >> file1 | |
5 $ echo "added file2" > file2 | |
6 $ hg add file1 file2 | |
7 $ hg commit -m "added file1 and file2" | |
8 | |
9 $ echo "changed file1" >> file1 | |
10 $ hg commit -m "changed file1" | |
11 | |
12 $ hg -q log | |
13 1:dfab7f3c2efb | |
14 0:c3fa057dd86f | |
15 $ hg id | |
16 dfab7f3c2efb tip | |
17 | |
18 $ hg update -C 0 | |
19 1 files updated, 0 files merged, 0 files removed, 0 files unresolved | |
20 $ hg id | |
21 c3fa057dd86f | |
22 | |
23 $ echo "changed file1" >> file1 | |
24 $ hg id | |
25 c3fa057dd86f+ | |
26 | |
27 $ hg revert --no-backup --all | |
28 reverting file1 | |
29 $ hg diff | |
30 $ hg status | |
31 $ hg id | |
32 c3fa057dd86f | |
33 | |
34 $ hg update | |
35 1 files updated, 0 files merged, 0 files removed, 0 files unresolved | |
36 $ hg diff | |
37 $ hg status | |
38 $ hg id | |
39 dfab7f3c2efb tip | |
40 | |
41 $ hg update -C 0 | |
42 1 files updated, 0 files merged, 0 files removed, 0 files unresolved | |
43 $ echo "changed file1 different" >> file1 | |
792
49ec802b4a16
Added tests for bug with three-way-merging of old tip, tip and cwd.
Thomas Arendsen Hein <thomas@intevation.de>
parents:
diff
changeset
|
44 |
12279 | 45 $ hg update |
46 merging file1 | |
26614
ef1eb6df7071
simplemerge: move conflict warning message to filemerge
Siddharth Agarwal <sid0@fb.com>
parents:
21693
diff
changeset
|
47 warning: conflicts while merging file1! (edit, then use 'hg resolve --mark') |
12279 | 48 0 files updated, 0 files merged, 0 files removed, 1 files unresolved |
49 use 'hg resolve' to retry unresolved file merges | |
12316
4134686b83e1
tests: add exit codes to unified tests
Matt Mackall <mpm@selenic.com>
parents:
12279
diff
changeset
|
50 [1] |
12279 | 51 |
52 $ hg diff --nodates | |
53 diff -r dfab7f3c2efb file1 | |
54 --- a/file1 | |
55 +++ b/file1 | |
56 @@ -1,3 +1,7 @@ | |
57 added file1 | |
58 another line of text | |
30460
ce3a133f71b3
conflicts: make spacing consistent in conflict markers
Kostia Balytskyi <ikostia@fb.com>
parents:
26614
diff
changeset
|
59 +<<<<<<< working copy: c3fa057dd86f - test: added file1 and file2 |
12279 | 60 +changed file1 different |
61 +======= | |
62 changed file1 | |
21693
9c35f3a8cac4
merge: drop the quotes around commit description
Pierre-Yves David <pierre-yves.david@fb.com>
parents:
21537
diff
changeset
|
63 +>>>>>>> destination: dfab7f3c2efb - test: changed file1 |
792
49ec802b4a16
Added tests for bug with three-way-merging of old tip, tip and cwd.
Thomas Arendsen Hein <thomas@intevation.de>
parents:
diff
changeset
|
64 |
12279 | 65 $ hg status |
66 M file1 | |
67 ? file1.orig | |
68 $ hg id | |
69 dfab7f3c2efb+ tip | |
70 | |
71 $ hg revert --no-backup --all | |
72 reverting file1 | |
73 $ hg diff | |
74 $ hg status | |
75 ? file1.orig | |
76 $ hg id | |
77 dfab7f3c2efb tip | |
78 | |
79 $ hg revert -r tip --no-backup --all | |
80 $ hg diff | |
81 $ hg status | |
82 ? file1.orig | |
83 $ hg id | |
84 dfab7f3c2efb tip | |
85 | |
86 $ hg update -C | |
87 0 files updated, 0 files merged, 0 files removed, 0 files unresolved | |
88 $ hg diff | |
89 $ hg status | |
90 ? file1.orig | |
91 $ hg id | |
92 dfab7f3c2efb tip | |
93 |