view tests/test-convert-bzr.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

#require bzr

  $ . "$TESTDIR/bzr-definitions"

create and rename on the same file in the same step

  $ mkdir test-createandrename
  $ cd test-createandrename
  $ bzr init -q source

test empty repo conversion (issue3233)

  $ hg convert source source-hg
  initializing destination source-hg repository
  scanning source...
  sorting...
  converting...

back to the rename stuff

  $ cd source
  $ echo a > a
  $ echo c > c
  $ echo e > e
  $ bzr add -q a c e
  $ bzr commit -q -m 'Initial add: a, c, e'
  $ bzr mv a b
  a => b
  $ bzr mv c d
  c => d
  $ bzr mv e f
  e => f
  $ echo a2 >> a
  $ mkdir e
  $ bzr add -q a e
  $ bzr commit -q -m 'rename a into b, create a, rename c into d'
  $ cd ..
  $ hg convert source source-hg
  scanning source...
  sorting...
  converting...
  1 Initial add: a, c, e
  0 rename a into b, create a, rename c into d
  $ glog -R source-hg
  o  1@source "rename a into b, create a, rename c into d" files+: [b d f], files-: [c e], files: [a]
  |
  o  0@source "Initial add: a, c, e" files+: [a c e], files-: [], files: []
  

manifest

  $ hg manifest -R source-hg -r tip
  a
  b
  d
  f

test --rev option

  $ hg convert -r 1 source source-1-hg
  initializing destination source-1-hg repository
  scanning source...
  sorting...
  converting...
  0 Initial add: a, c, e
  $ glog -R source-1-hg
  o  0@source "Initial add: a, c, e" files+: [a c e], files-: [], files: []
  

test with filemap

  $ cat > filemap <<EOF
  > exclude a
  > EOF
  $ hg convert --filemap filemap source source-filemap-hg
  initializing destination source-filemap-hg repository
  scanning source...
  sorting...
  converting...
  1 Initial add: a, c, e
  0 rename a into b, create a, rename c into d
  $ hg -R source-filemap-hg manifest -r tip
  b
  d
  f

convert from lightweight checkout

  $ bzr checkout --lightweight source source-light
  $ hg convert -s bzr source-light source-light-hg
  initializing destination source-light-hg repository
  warning: lightweight checkouts may cause conversion failures, try with a regular branch instead.
  $TESTTMP/test-createandrename/source-light does not look like a Bazaar repository
  abort: source-light: missing or unsupported repository
  [255]

extract timestamps that look just like hg's {date|isodate}:
yyyy-mm-dd HH:MM zzzz (no seconds!)
compare timestamps

  $ cd source
  $ bzr log | \
  >   sed '/timestamp/!d;s/.\{15\}\([0-9: -]\{16\}\):.. \(.[0-9]\{4\}\)/\1 \2/' \
  >   > ../bzr-timestamps
  $ cd ..
  $ hg -R source-hg log --template "{date|isodate}\n" > hg-timestamps
  $ cmp bzr-timestamps hg-timestamps || diff -u bzr-timestamps hg-timestamps
  $ cd ..

merge

  $ mkdir test-merge
  $ cd test-merge
  $ cat > helper.py <<EOF
  > import sys
  > from bzrlib import workingtree
  > wt = workingtree.WorkingTree.open('.')
  > 
  > message, stamp = sys.argv[1:]
  > wt.commit(message, timestamp=int(stamp))
  > EOF
  $ bzr init -q source
  $ cd source
  $ echo content > a
  $ echo content2 > b
  $ bzr add -q a b
  $ bzr commit -q -m 'Initial add'
  $ cd ..
  $ bzr branch -q source source-improve
  $ cd source
  $ echo more >> a
  $ "$PYTHON" ../helper.py 'Editing a' 100
  $ cd ../source-improve
  $ echo content3 >> b
  $ "$PYTHON" ../helper.py 'Editing b' 200
  $ cd ../source
  $ bzr merge -q ../source-improve
  $ bzr commit -q -m 'Merged improve branch'
  $ cd ..
  $ hg convert --datesort source source-hg
  initializing destination source-hg repository
  scanning source...
  sorting...
  converting...
  3 Initial add
  2 Editing a
  1 Editing b
  0 Merged improve branch
  $ glog -R source-hg
  o    3@source "Merged improve branch" files+: [], files-: [], files: [b]
  |\
  | o  2@source-improve "Editing b" files+: [], files-: [], files: [b]
  | |
  o |  1@source "Editing a" files+: [], files-: [], files: [a]
  |/
  o  0@source "Initial add" files+: [a b], files-: [], files: []
  
  $ cd ..

#if symlink execbit

symlinks and executable files

  $ mkdir test-symlinks
  $ cd test-symlinks
  $ bzr init -q source
  $ cd source
  $ touch program
  $ chmod +x program
  $ ln -s program altname
  $ mkdir d
  $ echo a > d/a
  $ ln -s a syma
  $ bzr add -q altname program syma d/a
  $ bzr commit -q -m 'Initial setup'
  $ touch newprog
  $ chmod +x newprog
  $ rm altname
  $ ln -s newprog altname
  $ chmod -x program
  $ bzr add -q newprog
  $ bzr commit -q -m 'Symlink changed, x bits changed'
  $ cd ..
  $ hg convert source source-hg
  initializing destination source-hg repository
  scanning source...
  sorting...
  converting...
  1 Initial setup
  0 Symlink changed, x bits changed
  $ manifest source-hg 0
  % manifest of 0
  644 @ altname
  644   d/a
  755 * program
  644 @ syma
  $ manifest source-hg tip
  % manifest of tip
  644 @ altname
  644   d/a
  755 * newprog
  644   program
  644 @ syma

test the symlinks can be recreated

  $ cd source-hg
  $ hg up
  5 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg cat syma; echo
  a
  $ cd ../..

#endif

Multiple branches

  $ bzr init-repo -q --no-trees repo
  $ bzr init -q repo/trunk
  $ bzr co repo/trunk repo-trunk
  $ cd repo-trunk
  $ echo a > a
  $ bzr add -q a
  $ bzr ci -qm adda
  $ bzr tag trunk-tag
  Created tag trunk-tag.
  $ bzr switch -b branch
  Tree is up to date at revision 1.
  Switched to branch: *repo/branch/ (glob)
  $ sleep 1
  $ echo b > b
  $ bzr add -q b
  $ bzr ci -qm addb
  $ bzr tag branch-tag
  Created tag branch-tag.
  $ bzr switch --force ../repo/trunk
  Updated to revision 1.
  Switched to branch: */repo/trunk/ (glob)
  $ sleep 1
  $ echo a >> a
  $ bzr ci -qm changea
  $ cd ..
  $ hg convert --datesort repo repo-bzr
  initializing destination repo-bzr repository
  scanning source...
  sorting...
  converting...
  2 adda
  1 addb
  0 changea
  updating tags
  $ (cd repo-bzr; glog)
  o  3@default "update tags" files+: [.hgtags], files-: [], files: []
  |
  o  2@default "changea" files+: [], files-: [], files: [a]
  |
  | o  1@branch "addb" files+: [b], files-: [], files: []
  |/
  o  0@default "adda" files+: [a], files-: [], files: []
  

Test tags (converted identifiers are not stable because bzr ones are
not and get incorporated in extra fields).

  $ hg -R repo-bzr tags
  tip                                3:* (glob)
  branch-tag                         1:* (glob)
  trunk-tag                          0:* (glob)

Nested repositories (issue3254)

  $ bzr init-repo -q --no-trees repo/inner
  $ bzr init -q repo/inner/trunk
  $ bzr co repo/inner/trunk inner-trunk
  $ cd inner-trunk
  $ echo b > b
  $ bzr add -q b
  $ bzr ci -qm addb
  $ cd ..
  $ hg convert --datesort repo noinner-bzr
  initializing destination noinner-bzr repository
  scanning source...
  sorting...
  converting...
  2 adda
  1 addb
  0 changea
  updating tags