view tests/test-githelp.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

  $ cat >> $HGRCPATH << EOF
  > [extensions]
  > githelp =
  > EOF

  $ hg init repo
  $ cd repo
  $ echo foo > test_file
  $ mkdir dir
  $ echo foo > dir/file
  $ echo foo > removed_file
  $ echo foo > deleted_file
  $ hg add -q .
  $ hg commit -m 'bar'
  $ hg bookmark both
  $ touch both
  $ touch untracked_file
  $ hg remove removed_file
  $ rm deleted_file

githelp on a single command should succeed
  $ hg githelp -- commit
  hg commit
  $ hg githelp -- git commit
  hg commit

githelp should fail nicely if we don't give it arguments
  $ hg githelp
  abort: missing git command - usage: hg githelp -- <git command>
  [255]
  $ hg githelp -- git
  abort: missing git command - usage: hg githelp -- <git command>
  [255]

githelp on a command with options should succeed
  $ hg githelp -- commit -pm "abc"
  hg commit --interactive -m 'abc'

githelp on a command with standalone unrecognized option should succeed with warning
  $ hg githelp -- commit -p -v
  ignoring unknown option -v
  hg commit --interactive

githelp on a command with unrecognized option packed with other options should fail with error
  $ hg githelp -- commit -pv
  abort: unknown option 'v' packed with other options
  (please try passing the option as its own flag: -v)
  [255]

githelp for git rebase --skip
  $ hg githelp -- git rebase --skip
  hg revert --all -r .
  hg rebase --continue

githelp for git commit --amend (hg commit --amend pulls up an editor)
  $ hg githelp -- commit --amend
  hg commit --amend

githelp for git commit --amend --no-edit (hg amend does not pull up an editor)
  $ hg githelp -- commit --amend --no-edit
  hg amend

githelp for git checkout -- . (checking out a directory)
  $ hg githelp -- checkout -- .
  note: use --no-backup to avoid creating .orig files
  
  hg revert .

githelp for git checkout "HEAD^" (should still work to pass a rev)
  $ hg githelp -- checkout "HEAD^"
  hg update .^

githelp checkout: args after -- should be treated as paths no matter what
  $ hg githelp -- checkout -- HEAD
  note: use --no-backup to avoid creating .orig files
  
  hg revert HEAD

githelp for git checkout with rev and path
  $ hg githelp -- checkout "HEAD^" -- file.txt
  note: use --no-backup to avoid creating .orig files
  
  hg revert -r .^ file.txt

githelp for git with rev and path, without separator
  $ hg githelp -- checkout "HEAD^" file.txt
  note: use --no-backup to avoid creating .orig files
  
  hg revert -r .^ file.txt

githelp for checkout with a file as first argument
  $ hg githelp -- checkout test_file
  note: use --no-backup to avoid creating .orig files
  
  hg revert test_file

githelp for checkout with a removed file as first argument
  $ hg githelp -- checkout removed_file
  note: use --no-backup to avoid creating .orig files
  
  hg revert removed_file

githelp for checkout with a deleted file as first argument
  $ hg githelp -- checkout deleted_file
  note: use --no-backup to avoid creating .orig files
  
  hg revert deleted_file

githelp for checkout with a untracked file as first argument
  $ hg githelp -- checkout untracked_file
  note: use --no-backup to avoid creating .orig files
  
  hg revert untracked_file

githelp for checkout with a directory as first argument
  $ hg githelp -- checkout dir
  note: use --no-backup to avoid creating .orig files
  
  hg revert dir

githelp for checkout when not in repo root
  $ cd dir
  $ hg githelp -- checkout file
  note: use --no-backup to avoid creating .orig files
  
  hg revert file

  $ cd ..

githelp for checkout with an argument that is both a file and a revision
  $ hg githelp -- checkout both
  hg update both

githelp for checkout with the -p option
  $ hg githelp -- git checkout -p xyz
  hg revert -i -r xyz

  $ hg githelp -- git checkout -p xyz -- abc
  note: use --no-backup to avoid creating .orig files
  
  hg revert -i -r xyz abc

githelp for checkout with the -f option and a rev
  $ hg githelp -- git checkout -f xyz
  hg update -C xyz
  $ hg githelp -- git checkout --force xyz
  hg update -C xyz

githelp for checkout with the -f option without an arg
  $ hg githelp -- git checkout -f
  hg revert --all
  $ hg githelp -- git checkout --force
  hg revert --all

githelp for grep with pattern and path
  $ hg githelp -- grep shrubbery flib/intern/
  hg grep shrubbery flib/intern/

githelp for reset, checking ~ in git becomes ~1 in mercurial
  $ hg githelp -- reset HEAD~
  hg update .~1
  $ hg githelp -- reset "HEAD^"
  hg update .^
  $ hg githelp -- reset HEAD~3
  hg update .~3

  $ hg githelp -- reset --mixed HEAD
  note: --mixed has no meaning since Mercurial has no staging area
  
  hg update .
  $ hg githelp -- reset --soft HEAD
  note: --soft has no meaning since Mercurial has no staging area
  
  hg update .
  $ hg githelp -- reset --hard HEAD
  hg update --clean .

githelp for git show --name-status
  $ hg githelp -- git show --name-status
  hg log --style status -r .

githelp for git show --pretty=format: --name-status
  $ hg githelp -- git show --pretty=format: --name-status
  hg status --change .

githelp for show with no arguments
  $ hg githelp -- show
  hg export

githelp for show with a path
  $ hg githelp -- show test_file
  hg cat test_file

githelp for show with not a path:
  $ hg githelp -- show rev
  hg export rev

githelp for show with many arguments
  $ hg githelp -- show argone argtwo
  hg export argone argtwo
  $ hg githelp -- show test_file argone argtwo
  hg cat test_file argone argtwo

githelp for show with --unified options
  $ hg githelp -- show --unified=10
  hg export --config diff.unified=10
  $ hg githelp -- show -U100
  hg export --config diff.unified=100

githelp for show with a path and --unified
  $ hg githelp -- show -U20 test_file
  hg cat test_file --config diff.unified=20

githelp for stash drop without name
  $ hg githelp -- git stash drop
  hg shelve -d <shelve name>

githelp for stash drop with name
  $ hg githelp -- git stash drop xyz
  hg shelve -d xyz

githelp for whatchanged should show deprecated message
  $ hg githelp -- whatchanged -p
  this command has been deprecated in the git project, thus isn't supported by this tool
  

githelp for git branch -m renaming
  $ hg githelp -- git branch -m old new
  hg bookmark -m old new

When the old name is omitted, git branch -m new renames the current branch.
  $ hg githelp -- git branch -m new
  hg bookmark -m `hg log -T"{activebookmark}" -r .` new

Branch deletion in git strips commits
  $ hg githelp -- git branch -d
  hg strip -B
  $ hg githelp -- git branch -d feature
  hg strip -B feature -B
  $ hg githelp -- git branch --delete experiment1 experiment2
  hg strip -B experiment1 -B experiment2 -B

githelp for reuse message using the shorthand
  $ hg githelp -- git commit -C deadbeef
  hg commit -M deadbeef

githelp for reuse message using the the long version
  $ hg githelp -- git commit --reuse-message deadbeef
  hg commit -M deadbeef

githelp for apply with no options
  $ hg githelp -- apply
  hg import --no-commit

githelp for apply with directory strip custom
  $ hg githelp -- apply -p 5
  hg import --no-commit -p 5

git merge-base
  $ hg githelp -- git merge-base --is-ancestor
  ignoring unknown option --is-ancestor
  note: ancestors() is part of the revset language
  (learn more about revsets with 'hg help revsets')
  
  hg log -T '{node}\n' -r 'ancestor(A,B)'

githelp for git blame
  $ hg githelp -- git blame
  hg annotate -udl

githelp for add

  $ hg githelp -- git add
  hg add

  $ hg githelp -- git add -p
  note: Mercurial will commit when complete, as there is no staging area in Mercurial
  
  hg commit --interactive

  $ hg githelp -- git add --all
  note: use hg addremove to remove files that have been deleted
  
  hg add

githelp for reflog

  $ hg githelp -- git reflog
  hg journal
  
  note: in hg commits can be deleted from repo but we always have backups

  $ hg githelp -- git reflog --all
  hg journal --all
  
  note: in hg commits can be deleted from repo but we always have backups