view tests/test-subrepo-relative-path.t @ 40326:fed697fa1734

sqlitestore: file storage backend using SQLite

This commit provides an extension which uses SQLite to store file
data (as opposed to revlogs).

As the inline documentation describes, there are still several
aspects to the extension that are incomplete. But it's a start.
The extension does support basic clone, checkout, and commit
workflows, which makes it suitable for simple use cases.

One notable missing feature is support for "bundlerepos." This is
probably responsible for the most test failures when the extension
is activated as part of the test suite.

All revision data is stored in SQLite. Data is stored as zstd
compressed chunks (default if zstd is available), zlib compressed
chunks (default if zstd is not available), or raw chunks (if
configured or if a compressed delta is not smaller than the raw
delta). This makes things very similar to revlogs.

Unlike revlogs, the extension doesn't yet enforce a limit on delta
chain length. This is an obvious limitation and should be addressed.
This is somewhat mitigated by the use of zstd, which is much faster
than zlib to decompress.

There is a dedicated table for storing deltas. Deltas are stored
by the SHA-1 hash of their uncompressed content. The "fileindex" table
has columns that reference the delta for each revision and the base
delta that delta should be applied against. A recursive SQL query
is used to resolve the delta chain along with the delta data.

By storing deltas by hash, we are able to de-duplicate delta storage!
With revlogs, the same deltas in different revlogs would result in
duplicate storage of that delta. In this scheme, inserting the
duplicate delta is a no-op and delta chains simply reference the
existing delta.

When initially implementing this extension, I did not have
content-indexed deltas and deltas could be duplicated across files
(just like revlogs). When I implemented content-indexed deltas, the
size of the SQLite database for a full clone of mozilla-unified
dropped:

before: 2,554,261,504 bytes
after:  2,488,754,176 bytes

Surprisingly, this is still larger than the bytes size of revlog
files:

revlog files: 2,104,861,230 bytes
du -b:        2,254,381,614

I would have expected storage to be smaller since we're not limiting
delta chain length and since we're using zstd instead of zlib. I
suspect the SQLite indexes and per-column overhead account for the
bulk of the differences. (Keep in mind that revlog uses a 64-byte
packed struct for revision index data and deltas are stored without
padding. Aside from the 12 unused bytes in the 32 byte node field,
revlogs are pretty efficient.) Another source of overhead is file
name storage. With revlogs, file names are stored in the filesystem.
But with SQLite, we need to store file names in the database. This is
roughly equivalent to the size of the fncache file, which for the
mozilla-unified repository is ~34MB.

Since the SQLite database isn't append-only and since delta chains
can reference any delta, this opens some interesting possibilities.
For example, we could store deltas in reverse, such that fulltexts
are stored for newer revisions and deltas are applied to reconstruct
older revisions. This is likely a more optimal storage strategy for
version control, as new data tends to be more frequently accessed
than old data. We would obviously need wire protocol support for
transferring revision data from newest to oldest. And we would
probably need some kind of mechanism for "re-encoding" stores. But
it should be doable.

This extension is very much experimental quality. There are a handful
of features that don't work. It probably isn't suitable for day-to-day
use. But it could be used in limited cases (e.g. read-only checkouts
like in CI). And it is also a good proving ground for alternate
storage backends. As we continue to define interfaces for all things
storage, it will be useful to have a viable alternate storage backend
to see how things shake out in practice.

test-storage.py passes on Python 2 and introduces no new test failures on
Python 3. Having the storage-level unit tests has proved to be insanely
useful when developing this extension. Those tests caught numerous bugs
during development and I'm convinced this style of testing is the way
forward for ensuring alternate storage backends work as intended. Of
course, test coverage isn't close to what it needs to be. But it is
a start. And what coverage we have gives me confidence that basic store
functionality is implemented properly.

Differential Revision: https://phab.mercurial-scm.org/D4928

Preparing the subrepository 'sub'

  $ hg init sub
  $ echo sub > sub/sub
  $ hg add -R sub
  adding sub/sub
  $ hg commit -R sub -m "sub import"

Preparing the 'main' repo which depends on the subrepo 'sub'

  $ hg init main
  $ echo main > main/main
  $ echo "sub = ../sub" > main/.hgsub
  $ hg clone sub main/sub
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg add -R main
  adding main/.hgsub
  adding main/main
  $ hg commit -R main -m "main import"

Cleaning both repositories, just as a clone -U

  $ hg up -C -R sub null
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ hg up -C -R main null
  0 files updated, 0 files merged, 3 files removed, 0 files unresolved
  $ rm -rf main/sub

hide outer repo
  $ hg init

Serving them both using hgweb

  $ printf '[paths]\n/main = main\nsub = sub\n' > webdir.conf
  $ hg serve --webdir-conf webdir.conf -a localhost -p $HGPORT \
  >    -A /dev/null -E /dev/null --pid-file hg.pid -d
  $ cat hg.pid >> $DAEMON_PIDS

Clone main from hgweb

  $ hg clone "http://user:pass@localhost:$HGPORT/main" cloned
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 3 changes to 3 files
  new changesets fdfeeb3e979e
  updating to branch default
  cloning subrepo sub from http://user@localhost:$HGPORT/sub
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  new changesets 863c1745b441
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved

Ensure that subrepos pay attention to default:pushurl

  $ cat > cloned/.hg/hgrc << EOF
  > [paths]
  > default:pushurl = http://user:pass@localhost:$HGPORT/main
  > EOF

  $ hg -R cloned out -S --config paths.default=bogus://invalid
  comparing with http://user:***@localhost:$HGPORT/main
  searching for changes
  no changes found
  comparing with http://user:***@localhost:$HGPORT/sub
  searching for changes
  no changes found
  [1]

TODO: Figure out why, if the password is left out of the default:pushurl URL,
this says "no changes made to subrepo sub since last push".  It looks like from
the original clone command above, the password is getting stripped off, not
just masked out, and that would make the hashed URL different.

  $ hg -R cloned push --config paths.default=bogus://invalid
  pushing to http://user:***@localhost:$HGPORT/main
  pushing subrepo sub to http://user:***@localhost:$HGPORT/sub
  searching for changes
  no changes found
  searching for changes
  no changes found
  abort: HTTP Error 403: ssl required
  [255]

Checking cloned repo ids

  $ hg id -R cloned
  fdfeeb3e979e tip
  $ hg id -R cloned/sub
  863c1745b441 tip

subrepo debug for 'main' clone

  $ hg debugsub -R cloned
  path sub
   source   ../sub
   revision 863c1745b441bd97a8c4a096e87793073f4fb215

Test sharing with a remote URL reference

  $ hg init absolute_subrepo
  $ cd absolute_subrepo
  $ echo foo > foo.txt
  $ hg ci -Am 'initial commit'
  adding foo.txt
  $ echo "sub = http://localhost:$HGPORT/sub" > .hgsub
  $ hg ci -Am 'add absolute subrepo'
  adding .hgsub
  $ cd ..

Clone pooling works for local clones with a remote subrepo reference.  The
subrepo is cloned to the pool and shared from there, so that all clones will
share the same subrepo.

  $ hg --config extensions.share= --config share.pool=$TESTTMP/pool \
  >    clone absolute_subrepo cloned_from_abs
  (sharing from new pooled repository 8d6a2f1e993b34b6557de0042cfe825ae12a8dae)
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 2 changesets with 3 changes to 3 files
  new changesets 8d6a2f1e993b:* (glob)
  searching for changes
  no changes found
  updating working directory
  cloning subrepo sub from http://localhost:$HGPORT/sub
  (sharing from new pooled repository 863c1745b441bd97a8c4a096e87793073f4fb215)
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  new changesets 863c1745b441
  searching for changes
  no changes found
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved

Vanilla sharing with a subrepo remote path reference will clone the subrepo.
Each share of these top level repos will end up with independent subrepo copies
(potentially leaving the shared parent with dangling cset references).

  $ hg --config extensions.share= share absolute_subrepo shared_from_abs
  updating working directory
  cloning subrepo sub from http://localhost:$HGPORT/sub
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  new changesets 863c1745b441
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ hg --config extensions.share= share -U absolute_subrepo shared_from_abs2
  $ hg -R shared_from_abs2 update -r tip
  cloning subrepo sub from http://localhost:$HGPORT/sub
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  new changesets 863c1745b441
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved

A parent repo without its subrepo available locally can be shared if the
subrepo is referenced by absolute path.

  $ hg clone -U absolute_subrepo cloned_null_from_abs
  $ hg --config extensions.share= share cloned_null_from_abs shared_from_null_abs
  updating working directory
  cloning subrepo sub from http://localhost:$HGPORT/sub
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  new changesets 863c1745b441
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ killdaemons.py

subrepo paths with ssh urls

  $ hg clone -e "\"$PYTHON\" \"$TESTDIR/dummyssh\"" ssh://user@dummy/cloned sshclone
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 3 changes to 3 files
  new changesets fdfeeb3e979e
  updating to branch default
  cloning subrepo sub from ssh://user@dummy/sub
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  new changesets 863c1745b441
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ hg -R sshclone push -e "\"$PYTHON\" \"$TESTDIR/dummyssh\"" ssh://user@dummy/`pwd`/cloned
  pushing to ssh://user@dummy/$TESTTMP/cloned
  pushing subrepo sub to ssh://user@dummy/$TESTTMP/sub
  searching for changes
  no changes found
  searching for changes
  no changes found
  [1]

  $ cat dummylog
  Got arguments 1:user@dummy 2:hg -R cloned serve --stdio
  Got arguments 1:user@dummy 2:hg -R sub serve --stdio
  Got arguments 1:user@dummy 2:hg -R $TESTTMP/cloned serve --stdio
  Got arguments 1:user@dummy 2:hg -R $TESTTMP/sub serve --stdio