view tests/test-largefiles-cache.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

Create user cache directory

  $ USERCACHE=`pwd`/cache; export USERCACHE
  $ cat <<EOF >> ${HGRCPATH}
  > [extensions]
  > hgext.largefiles=
  > [largefiles]
  > usercache=${USERCACHE}
  > EOF
  $ mkdir -p ${USERCACHE}

Create source repo, and commit adding largefile.

  $ hg init src
  $ cd src
  $ echo large > large
  $ hg add --large large
  $ hg commit -m 'add largefile'
  $ hg rm large
  $ hg commit -m 'branchhead without largefile' large
  $ hg up -qr 0
  $ rm large
  $ echo "0000000000000000000000000000000000000000" > .hglf/large
  $ hg commit -m 'commit missing file with corrupt standin' large
  abort: large: file not found!
  [255]
  $ hg up -Cqr 0
  $ cd ..

Discard all cached largefiles in USERCACHE

  $ rm -rf ${USERCACHE}

Create mirror repo, and pull from source without largefile:
"pull" is used instead of "clone" for suppression of (1) updating to
tip (= caching largefile from source repo), and (2) recording source
repo as "default" path in .hg/hgrc.

  $ hg init mirror
  $ cd mirror
  $ hg pull ../src
  pulling from ../src
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 2 changesets with 1 changes to 1 files
  new changesets eb85d9124f3f:26c18ce05e4e
  (run 'hg update' to get a working copy)

Update working directory to "tip", which requires largefile("large"),
but there is no cache file for it.  So, hg must treat it as
"missing"(!) file.

  $ hg update -r0
  getting changed largefiles
  large: largefile 7f7097b041ccf68cc5561e9600da4655d21c6d18 not available from file:/*/$TESTTMP/mirror (glob)
  0 largefiles updated, 0 removed
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg status
  ! large

Update working directory to null: this cleanup .hg/largefiles/dirstate

  $ hg update null
  getting changed largefiles
  0 largefiles updated, 0 removed
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

Update working directory to tip, again.

  $ hg update -r0
  getting changed largefiles
  large: largefile 7f7097b041ccf68cc5561e9600da4655d21c6d18 not available from file:/*/$TESTTMP/mirror (glob)
  0 largefiles updated, 0 removed
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg status
  ! large
  $ cd ..

Verify that largefiles from pulled branchheads are fetched, also to an empty repo

  $ hg init mirror2
  $ hg -R mirror2 pull src -r0
  pulling from src
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  new changesets eb85d9124f3f
  (run 'hg update' to get a working copy)

#if unix-permissions

Portable way to print file permissions:

  $ cat > ls-l.py <<EOF
  > #!$PYTHON
  > from __future__ import absolute_import, print_function
  > import os
  > import sys
  > path = sys.argv[1]
  > print('%03o' % (os.lstat(path).st_mode & 0o777))
  > EOF
  $ chmod +x ls-l.py

Test that files in .hg/largefiles inherit mode from .hg/store, not
from file in working copy:

  $ cd src
  $ chmod 750 .hg/store
  $ chmod 660 large
  $ echo change >> large
  $ hg commit -m change
  created new head
  $ ../ls-l.py .hg/largefiles/e151b474069de4ca6898f67ce2f2a7263adf8fea
  640

Test permission of with files in .hg/largefiles created by update:

  $ cd ../mirror
  $ rm -r "$USERCACHE" .hg/largefiles # avoid links
  $ chmod 750 .hg/store
  $ hg pull ../src --update -q
  $ ../ls-l.py .hg/largefiles/e151b474069de4ca6898f67ce2f2a7263adf8fea
  640

Test permission of files created by push:

  $ hg serve -R ../src -d -p $HGPORT --pid-file hg.pid \
  >          --config "web.allow_push=*" --config web.push_ssl=no
  $ cat hg.pid >> $DAEMON_PIDS

  $ echo change >> large
  $ hg commit -m change

  $ rm -r "$USERCACHE"

  $ hg push -q http://localhost:$HGPORT/

  $ ../ls-l.py ../src/.hg/largefiles/b734e14a0971e370408ab9bce8d56d8485e368a9
  640

  $ cd ..

#endif

Test issue 4053 (remove --after on a deleted, uncommitted file shouldn't say
it is missing, but a remove on a nonexistent unknown file still should.  Same
for a forget.)

  $ cd src
  $ touch x
  $ hg add x
  $ mv x y
  $ hg remove -A x y ENOENT
  ENOENT: * (glob)
  not removing y: file is untracked
  [1]
  $ hg add y
  $ mv y z
  $ hg forget y z ENOENT
  ENOENT: * (glob)
  not removing z: file is already untracked
  [1]

Largefiles are accessible from the share's store
  $ cd ..
  $ hg share -q src share_dst --config extensions.share=
  $ hg -R share_dst update -r0
  getting changed largefiles
  1 largefiles updated, 0 removed
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ echo modified > share_dst/large
  $ hg -R share_dst ci -m modified
  created new head

Only dirstate is in the local store for the share, and the largefile is in the
share source's local store.  Avoid the extra largefiles added in the unix
conditional above.
  $ hash=`hg -R share_dst cat share_dst/.hglf/large`
  $ echo $hash
  e2fb5f2139d086ded2cb600d5a91a196e76bf020

  $ find share_dst/.hg/largefiles/* | sort
  share_dst/.hg/largefiles/dirstate

  $ find src/.hg/largefiles/* | egrep "(dirstate|$hash)" | sort
  src/.hg/largefiles/dirstate
  src/.hg/largefiles/e2fb5f2139d086ded2cb600d5a91a196e76bf020

Verify that backwards compatibility is maintained for old storage layout
  $ mv src/.hg/largefiles/$hash share_dst/.hg/largefiles
  $ hg verify --quiet --lfa -R share_dst --config largefiles.usercache=

Inject corruption into the largefiles store and see how update handles that:

  $ cd src
  $ hg up -qC tip
  $ cat large
  modified
  $ rm large
  $ cat .hglf/large
  e2fb5f2139d086ded2cb600d5a91a196e76bf020
  $ mv .hg/largefiles/e2fb5f2139d086ded2cb600d5a91a196e76bf020 ..
  $ echo corruption > .hg/largefiles/e2fb5f2139d086ded2cb600d5a91a196e76bf020
  $ hg up -C
  getting changed largefiles
  large: data corruption in $TESTTMP/src/.hg/largefiles/e2fb5f2139d086ded2cb600d5a91a196e76bf020 with hash 6a7bb2556144babe3899b25e5428123735bb1e27
  0 largefiles updated, 0 removed
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  updated to "cd24c147f45c: modified"
  [12] other heads for branch "default" (re)
  $ hg st
  ! large
  ? z
  $ rm .hg/largefiles/e2fb5f2139d086ded2cb600d5a91a196e76bf020

#if serve

Test coverage of error handling from putlfile:

  $ mkdir $TESTTMP/mirrorcache
  $ hg serve -R ../mirror -d -p $HGPORT1 --pid-file hg.pid --config largefiles.usercache=$TESTTMP/mirrorcache
  $ cat hg.pid >> $DAEMON_PIDS

  $ hg push http://localhost:$HGPORT1 -f --config files.usercache=nocache
  pushing to http://localhost:$HGPORT1/
  searching for changes
  abort: remotestore: could not open file $TESTTMP/src/.hg/largefiles/e2fb5f2139d086ded2cb600d5a91a196e76bf020: HTTP Error 403: ssl required
  [255]

  $ rm .hg/largefiles/e2fb5f2139d086ded2cb600d5a91a196e76bf020

Test coverage of 'missing from store':

  $ hg serve -R ../mirror -d -p $HGPORT2 --pid-file hg.pid --config largefiles.usercache=$TESTTMP/mirrorcache --config "web.allow_push=*" --config web.push_ssl=no
  $ cat hg.pid >> $DAEMON_PIDS

  $ hg push http://localhost:$HGPORT2 -f --config largefiles.usercache=nocache
  pushing to http://localhost:$HGPORT2/
  searching for changes
  abort: largefile e2fb5f2139d086ded2cb600d5a91a196e76bf020 missing from store (needs to be uploaded)
  [255]

Verify that --lfrev controls which revisions are checked for largefiles to push

  $ hg push http://localhost:$HGPORT2 -f --config largefiles.usercache=nocache --lfrev tip
  pushing to http://localhost:$HGPORT2/
  searching for changes
  abort: largefile e2fb5f2139d086ded2cb600d5a91a196e76bf020 missing from store (needs to be uploaded)
  [255]

  $ hg push http://localhost:$HGPORT2 -f --config largefiles.usercache=nocache --lfrev null
  pushing to http://localhost:$HGPORT2/
  searching for changes
  remote: adding changesets
  remote: adding manifests
  remote: adding file changes
  remote: added 1 changesets with 1 changes to 1 files (+1 heads)

#endif