view tests/test-revset-legacy-lookup.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
  > [ui]
  > logtemplate="{rev}:{node|short} {desc} [{tags}]\n"
  > EOF

  $ hg init legacy-lookup
  $ cd legacy-lookup
  $ echo a > a
  $ hg add a
  $ hg commit -m 'first'
  $ echo aa > a
  $ hg commit -m 'second'
  $ hg log -G
  @  1:43114e71eddd second [tip]
  |
  o  0:a87874c6ec31 first []
  

Create a tag that looks like a revset

  $ hg tag 'rev(0)'
  $ hg log -G
  @  2:fb616635b18f Added tag rev(0) for changeset 43114e71eddd [tip]
  |
  o  1:43114e71eddd second [rev(0)]
  |
  o  0:a87874c6ec31 first []
  

See how various things are resolved
-----------------------------------

Revision numbers

  $ hg log -r '0'
  0:a87874c6ec31 first []
  $ hg log -r '1'
  1:43114e71eddd second [rev(0)]

"rev(x)" form (the one conflicting with the tags)
(resolved as a label)

  $ hg log -r 'rev(0)'
  1:43114e71eddd second [rev(0)]
  $ hg log -r 'rev(1)'
  1:43114e71eddd second [rev(0)]

same within a simple revspec
(still resolved as the label)

  $ hg log -r ':rev(0)'
  0:a87874c6ec31 first []
  1:43114e71eddd second [rev(0)]
  $ hg log -r 'rev(0):'
  1:43114e71eddd second [rev(0)]
  2:fb616635b18f Added tag rev(0) for changeset 43114e71eddd [tip]

within a more advances revset
(still resolved as the label)

  $ hg log -r 'rev(0) and branch(default)'
  0:a87874c6ec31 first []

with explicit revset resolution
(still resolved as the label)

  $ hg log -r 'revset(rev(0))'
  0:a87874c6ec31 first []

some of the above with quote to force its resolution as a label

  $ hg log -r ':"rev(0)"'
  0:a87874c6ec31 first []
  1:43114e71eddd second [rev(0)]
  $ hg log -r '"rev(0)":'
  1:43114e71eddd second [rev(0)]
  2:fb616635b18f Added tag rev(0) for changeset 43114e71eddd [tip]
  $ hg log -r '"rev(0)" and branch(default)'
  1:43114e71eddd second [rev(0)]

confusing bits within parents

  $ hg log -r '(rev(0))'
  0:a87874c6ec31 first []
  $ hg log -r '( rev(0))'
  0:a87874c6ec31 first []
  $ hg log -r '("rev(0)")'
  1:43114e71eddd second [rev(0)]

Test label with quote in them.

  $ hg tag '"foo"'

  $ hg log -r '"foo"'
  2:fb616635b18f Added tag rev(0) for changeset 43114e71eddd ["foo"]
  $ hg log -r '("foo")'
  abort: unknown revision 'foo'!
  [255]
  $ hg log -r 'revset("foo")'
  abort: unknown revision 'foo'!
  [255]
  $ hg log -r '("\"foo\"")'
  2:fb616635b18f Added tag rev(0) for changeset 43114e71eddd ["foo"]
  $ hg log -r 'revset("\"foo\"")'
  2:fb616635b18f Added tag rev(0) for changeset 43114e71eddd ["foo"]

Test label with dash in them.

  $ hg tag 'foo-bar'

  $ hg log -r 'foo-bar'
  3:a50aae922707 Added tag "foo" for changeset fb616635b18f [foo-bar]
  $ hg log -r '(foo-bar)'
  3:a50aae922707 Added tag "foo" for changeset fb616635b18f [foo-bar]
  $ hg log -r '"foo-bar"'
  3:a50aae922707 Added tag "foo" for changeset fb616635b18f [foo-bar]
  $ hg log -r '("foo-bar")'
  3:a50aae922707 Added tag "foo" for changeset fb616635b18f [foo-bar]

Test label with + in them.

  $ hg tag 'foo+bar'

  $ hg log -r 'foo+bar'
  4:bbf52b87b370 Added tag foo-bar for changeset a50aae922707 [foo+bar]
  $ hg log -r '(foo+bar)'
  abort: unknown revision 'foo'!
  [255]
  $ hg log -r 'revset(foo+bar)'
  abort: unknown revision 'foo'!
  [255]
  $ hg log -r '"foo+bar"'
  4:bbf52b87b370 Added tag foo-bar for changeset a50aae922707 [foo+bar]
  $ hg log -r '("foo+bar")'
  4:bbf52b87b370 Added tag foo-bar for changeset a50aae922707 [foo+bar]

Test tag with numeric version number.

  $ hg tag '1.2'

  $ hg log -r '1.2'
  5:ff42fde8edbb Added tag foo+bar for changeset bbf52b87b370 [1.2]
  $ hg log -r '(1.2)'
  5:ff42fde8edbb Added tag foo+bar for changeset bbf52b87b370 [1.2]
  $ hg log -r 'revset(1.2)'
  5:ff42fde8edbb Added tag foo+bar for changeset bbf52b87b370 [1.2]
  $ hg log -r '"1.2"'
  5:ff42fde8edbb Added tag foo+bar for changeset bbf52b87b370 [1.2]
  $ hg log -r '("1.2")'
  5:ff42fde8edbb Added tag foo+bar for changeset bbf52b87b370 [1.2]
  $ hg log -r '::"1.2"'
  0:a87874c6ec31 first []
  1:43114e71eddd second [rev(0)]
  2:fb616635b18f Added tag rev(0) for changeset 43114e71eddd ["foo"]
  3:a50aae922707 Added tag "foo" for changeset fb616635b18f [foo-bar]
  4:bbf52b87b370 Added tag foo-bar for changeset a50aae922707 [foo+bar]
  5:ff42fde8edbb Added tag foo+bar for changeset bbf52b87b370 [1.2]
  $ hg log -r '::1.2'
  0:a87874c6ec31 first []
  1:43114e71eddd second [rev(0)]
  2:fb616635b18f Added tag rev(0) for changeset 43114e71eddd ["foo"]
  3:a50aae922707 Added tag "foo" for changeset fb616635b18f [foo-bar]
  4:bbf52b87b370 Added tag foo-bar for changeset a50aae922707 [foo+bar]
  5:ff42fde8edbb Added tag foo+bar for changeset bbf52b87b370 [1.2]

Test tag with parenthesis (but not a valid revset)

  $ hg tag 'release_4.1(candidate1)'

  $ hg log -r 'release_4.1(candidate1)'
  6:db72e24fe069 Added tag 1.2 for changeset ff42fde8edbb [release_4.1(candidate1)]
  $ hg log -r '(release_4.1(candidate1))'
  hg: parse error: unknown identifier: release_4.1
  [255]
  $ hg log -r 'revset(release_4.1(candidate1))'
  hg: parse error: unknown identifier: release_4.1
  [255]
  $ hg log -r '"release_4.1(candidate1)"'
  6:db72e24fe069 Added tag 1.2 for changeset ff42fde8edbb [release_4.1(candidate1)]
  $ hg log -r '("release_4.1(candidate1)")'
  6:db72e24fe069 Added tag 1.2 for changeset ff42fde8edbb [release_4.1(candidate1)]
  $ hg log -r '::"release_4.1(candidate1)"'
  0:a87874c6ec31 first []
  1:43114e71eddd second [rev(0)]
  2:fb616635b18f Added tag rev(0) for changeset 43114e71eddd ["foo"]
  3:a50aae922707 Added tag "foo" for changeset fb616635b18f [foo-bar]
  4:bbf52b87b370 Added tag foo-bar for changeset a50aae922707 [foo+bar]
  5:ff42fde8edbb Added tag foo+bar for changeset bbf52b87b370 [1.2]
  6:db72e24fe069 Added tag 1.2 for changeset ff42fde8edbb [release_4.1(candidate1)]
  $ hg log -r '::release_4.1(candidate1)'
  hg: parse error: unknown identifier: release_4.1
  [255]

Test tag with parenthesis and other function like char

  $ hg tag 'release_4.1(arch=x86,arm)'

  $ hg log -r 'release_4.1(arch=x86,arm)'
  7:b29b25d7d687 Added tag release_4.1(candidate1) for changeset db72e24fe069 [release_4.1(arch=x86,arm)]
  $ hg log -r '(release_4.1(arch=x86,arm))'
  hg: parse error: unknown identifier: release_4.1
  [255]
  $ hg log -r 'revset(release_4.1(arch=x86,arm))'
  hg: parse error: unknown identifier: release_4.1
  [255]
  $ hg log -r '"release_4.1(arch=x86,arm)"'
  7:b29b25d7d687 Added tag release_4.1(candidate1) for changeset db72e24fe069 [release_4.1(arch=x86,arm)]
  $ hg log -r '("release_4.1(arch=x86,arm)")'
  7:b29b25d7d687 Added tag release_4.1(candidate1) for changeset db72e24fe069 [release_4.1(arch=x86,arm)]
  $ hg log -r '::"release_4.1(arch=x86,arm)"'
  0:a87874c6ec31 first []
  1:43114e71eddd second [rev(0)]
  2:fb616635b18f Added tag rev(0) for changeset 43114e71eddd ["foo"]
  3:a50aae922707 Added tag "foo" for changeset fb616635b18f [foo-bar]
  4:bbf52b87b370 Added tag foo-bar for changeset a50aae922707 [foo+bar]
  5:ff42fde8edbb Added tag foo+bar for changeset bbf52b87b370 [1.2]
  6:db72e24fe069 Added tag 1.2 for changeset ff42fde8edbb [release_4.1(candidate1)]
  7:b29b25d7d687 Added tag release_4.1(candidate1) for changeset db72e24fe069 [release_4.1(arch=x86,arm)]
  $ hg log -r '::release_4.1(arch=x86,arm)'
  hg: parse error: unknown identifier: release_4.1
  [255]

Test tag conflicting with revset function

  $ hg tag 'secret(team=foo,project=bar)'

  $ hg log -r 'secret(team=foo,project=bar)'
  8:6b2e2d4ea455 Added tag release_4.1(arch=x86,arm) for changeset b29b25d7d687 [secret(team=foo,project=bar)]
  $ hg log -r '(secret(team=foo,project=bar))'
  hg: parse error: secret takes no arguments
  [255]
  $ hg log -r 'revset(secret(team=foo,project=bar))'
  hg: parse error: secret takes no arguments
  [255]
  $ hg log -r '"secret(team=foo,project=bar)"'
  8:6b2e2d4ea455 Added tag release_4.1(arch=x86,arm) for changeset b29b25d7d687 [secret(team=foo,project=bar)]
  $ hg log -r '("secret(team=foo,project=bar)")'
  8:6b2e2d4ea455 Added tag release_4.1(arch=x86,arm) for changeset b29b25d7d687 [secret(team=foo,project=bar)]
  $ hg log -r '::"secret(team=foo,project=bar)"'
  0:a87874c6ec31 first []
  1:43114e71eddd second [rev(0)]
  2:fb616635b18f Added tag rev(0) for changeset 43114e71eddd ["foo"]
  3:a50aae922707 Added tag "foo" for changeset fb616635b18f [foo-bar]
  4:bbf52b87b370 Added tag foo-bar for changeset a50aae922707 [foo+bar]
  5:ff42fde8edbb Added tag foo+bar for changeset bbf52b87b370 [1.2]
  6:db72e24fe069 Added tag 1.2 for changeset ff42fde8edbb [release_4.1(candidate1)]
  7:b29b25d7d687 Added tag release_4.1(candidate1) for changeset db72e24fe069 [release_4.1(arch=x86,arm)]
  8:6b2e2d4ea455 Added tag release_4.1(arch=x86,arm) for changeset b29b25d7d687 [secret(team=foo,project=bar)]
  $ hg log -r '::secret(team=foo,project=bar)'
  hg: parse error: secret takes no arguments
  [255]

Test tag with space

  $ hg tag 'my little version'

  $ hg log -r 'my little version'
  9:269192bf8fc3 Added tag secret(team=foo,project=bar) for changeset 6b2e2d4ea455 [my little version]
  $ hg log -r '(my little version)'
  hg: parse error at 4: unexpected token: symbol
  ((my little version)
       ^ here)
  [255]
  $ hg log -r 'revset(my little version)'
  hg: parse error at 10: unexpected token: symbol
  (revset(my little version)
             ^ here)
  [255]
  $ hg log -r '"my little version"'
  9:269192bf8fc3 Added tag secret(team=foo,project=bar) for changeset 6b2e2d4ea455 [my little version]
  $ hg log -r '("my little version")'
  9:269192bf8fc3 Added tag secret(team=foo,project=bar) for changeset 6b2e2d4ea455 [my little version]
  $ hg log -r '::"my little version"'
  0:a87874c6ec31 first []
  1:43114e71eddd second [rev(0)]
  2:fb616635b18f Added tag rev(0) for changeset 43114e71eddd ["foo"]
  3:a50aae922707 Added tag "foo" for changeset fb616635b18f [foo-bar]
  4:bbf52b87b370 Added tag foo-bar for changeset a50aae922707 [foo+bar]
  5:ff42fde8edbb Added tag foo+bar for changeset bbf52b87b370 [1.2]
  6:db72e24fe069 Added tag 1.2 for changeset ff42fde8edbb [release_4.1(candidate1)]
  7:b29b25d7d687 Added tag release_4.1(candidate1) for changeset db72e24fe069 [release_4.1(arch=x86,arm)]
  8:6b2e2d4ea455 Added tag release_4.1(arch=x86,arm) for changeset b29b25d7d687 [secret(team=foo,project=bar)]
  9:269192bf8fc3 Added tag secret(team=foo,project=bar) for changeset 6b2e2d4ea455 [my little version]
  $ hg log -r '::my little version'
  hg: parse error at 5: invalid token
  (::my little version
        ^ here)
  [255]