view tests/test-win32text.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

  $ hg init t
  $ cd t
  $ cat > unix2dos.py <<EOF
  > import sys
  > 
  > for path in sys.argv[1:]:
  >     data = open(path, 'rb').read()
  >     data = data.replace(b'\n', b'\r\n')
  >     open(path, 'wb').write(data)
  > EOF
  $ echo '[hooks]' >> .hg/hgrc
  $ echo 'pretxncommit.crlf = python:hgext.win32text.forbidcrlf' >> .hg/hgrc
  $ echo 'pretxnchangegroup.crlf = python:hgext.win32text.forbidcrlf' >> .hg/hgrc
  $ cat .hg/hgrc
  [hooks]
  pretxncommit.crlf = python:hgext.win32text.forbidcrlf
  pretxnchangegroup.crlf = python:hgext.win32text.forbidcrlf

  $ echo hello > f
  $ hg add f

commit should succeed

  $ hg ci -m 1

  $ hg clone . ../zoz
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cp .hg/hgrc ../zoz/.hg
  $ "$PYTHON" unix2dos.py f

commit should fail

  $ hg ci -m 2.1
  attempt to commit or push text file(s) using CRLF line endings
  in f583ea08d42a: f
  transaction abort!
  rollback completed
  abort: pretxncommit.crlf hook failed
  [255]

  $ mv .hg/hgrc .hg/hgrc.bak

commits should succeed

  $ hg ci -m 2
  $ hg cp f g
  $ hg ci -m 2.2

push should fail

  $ hg push ../zoz
  pushing to ../zoz
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 2 changesets with 2 changes to 2 files
  attempt to commit or push text file(s) using CRLF line endings
  in bc2d09796734: g
  in b1aa5cde7ff4: f
  
  To prevent this mistake in your local repository,
  add to Mercurial.ini or .hg/hgrc:
  
  [hooks]
  pretxncommit.crlf = python:hgext.win32text.forbidcrlf
  
  and also consider adding:
  
  [extensions]
  win32text =
  [encode]
  ** = cleverencode:
  [decode]
  ** = cleverdecode:
  transaction abort!
  rollback completed
  abort: pretxnchangegroup.crlf hook failed
  [255]

  $ mv .hg/hgrc.bak .hg/hgrc
  $ echo hello > f
  $ hg rm g

commit should succeed

  $ hg ci -m 2.3

push should succeed

  $ hg push ../zoz
  pushing to ../zoz
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 3 changesets with 3 changes to 2 files

and now for something completely different

  $ mkdir d
  $ echo hello > d/f2
  $ "$PYTHON" unix2dos.py d/f2
  $ hg add d/f2
  $ hg ci -m 3
  attempt to commit or push text file(s) using CRLF line endings
  in 053ba1a3035a: d/f2
  transaction abort!
  rollback completed
  abort: pretxncommit.crlf hook failed
  [255]
  $ hg revert -a
  forgetting d/f2
  $ rm d/f2

  $ hg rem f
  $ hg ci -m 4

  $ "$PYTHON" -c 'open("bin", "wb").write(b"hello\x00\x0D\x0A")'
  $ hg add bin
  $ hg ci -m 5
  $ hg log -v
  changeset:   5:f0b1c8d75fce
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files:       bin
  description:
  5
  
  
  changeset:   4:77796dbcd4ad
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files:       f
  description:
  4
  
  
  changeset:   3:7c1b5430b350
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files:       f g
  description:
  2.3
  
  
  changeset:   2:bc2d09796734
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files:       g
  description:
  2.2
  
  
  changeset:   1:b1aa5cde7ff4
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files:       f
  description:
  2
  
  
  changeset:   0:fcf06d5c4e1d
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files:       f
  description:
  1
  
  
  $ hg clone . dupe
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ for x in a b c d; do echo content > dupe/$x; done
  $ hg -R dupe add
  adding dupe/a
  adding dupe/b
  adding dupe/c
  adding dupe/d
  $ "$PYTHON" unix2dos.py dupe/b dupe/c dupe/d
  $ hg -R dupe ci -m a dupe/a
  $ hg -R dupe ci -m b/c dupe/[bc]
  $ hg -R dupe ci -m d dupe/d
  $ hg -R dupe log -v
  changeset:   8:67ac5962ab43
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files:       d
  description:
  d
  
  
  changeset:   7:68c127d1834e
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files:       b c
  description:
  b/c
  
  
  changeset:   6:adbf8bf7f31d
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files:       a
  description:
  a
  
  
  changeset:   5:f0b1c8d75fce
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files:       bin
  description:
  5
  
  
  changeset:   4:77796dbcd4ad
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files:       f
  description:
  4
  
  
  changeset:   3:7c1b5430b350
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files:       f g
  description:
  2.3
  
  
  changeset:   2:bc2d09796734
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files:       g
  description:
  2.2
  
  
  changeset:   1:b1aa5cde7ff4
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files:       f
  description:
  2
  
  
  changeset:   0:fcf06d5c4e1d
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files:       f
  description:
  1
  
  
  $ hg pull dupe
  pulling from dupe
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 3 changesets with 4 changes to 4 files
  attempt to commit or push text file(s) using CRLF line endings
  in 67ac5962ab43: d
  in 68c127d1834e: b
  in 68c127d1834e: c
  
  To prevent this mistake in your local repository,
  add to Mercurial.ini or .hg/hgrc:
  
  [hooks]
  pretxncommit.crlf = python:hgext.win32text.forbidcrlf
  
  and also consider adding:
  
  [extensions]
  win32text =
  [encode]
  ** = cleverencode:
  [decode]
  ** = cleverdecode:
  transaction abort!
  rollback completed
  abort: pretxnchangegroup.crlf hook failed
  [255]

  $ hg log -v
  changeset:   5:f0b1c8d75fce
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files:       bin
  description:
  5
  
  
  changeset:   4:77796dbcd4ad
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files:       f
  description:
  4
  
  
  changeset:   3:7c1b5430b350
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files:       f g
  description:
  2.3
  
  
  changeset:   2:bc2d09796734
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files:       g
  description:
  2.2
  
  
  changeset:   1:b1aa5cde7ff4
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files:       f
  description:
  2
  
  
  changeset:   0:fcf06d5c4e1d
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files:       f
  description:
  1
  
  
  $ rm .hg/hgrc
  $ (echo some; echo text) > f3
  $ "$PYTHON" -c 'open("f4.bat", "wb").write(b"rem empty\x0D\x0A")'
  $ hg add f3 f4.bat
  $ hg ci -m 6
  $ cat bin
  hello\x00\r (esc)
  $ cat f3
  some
  text
  $ cat f4.bat
  rem empty\r (esc)

  $ echo '[extensions]' >> .hg/hgrc
  $ echo 'win32text = ' >> .hg/hgrc
  $ echo '[decode]' >> .hg/hgrc
  $ echo '** = cleverdecode:' >> .hg/hgrc
  $ echo '[encode]' >> .hg/hgrc
  $ echo '** = cleverencode:' >> .hg/hgrc
  $ cat .hg/hgrc
  [extensions]
  win32text = 
  [decode]
  ** = cleverdecode:
  [encode]
  ** = cleverencode:

Trigger deprecation warning:

  $ hg id -t
  win32text is deprecated: https://mercurial-scm.org/wiki/Win32TextExtension
  tip

Disable warning:

  $ echo '[win32text]' >> .hg/hgrc
  $ echo 'warn = no' >> .hg/hgrc
  $ hg id -t
  tip

  $ rm f3 f4.bat bin
  $ hg co -C
  WARNING: f4.bat already has CRLF line endings
  and does not need EOL conversion by the win32text plugin.
  Before your next commit, please reconsider your encode/decode settings in 
  Mercurial.ini or $TESTTMP/t/.hg/hgrc.
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cat bin
  hello\x00\r (esc)
  $ cat f3
  some\r (esc)
  text\r (esc)
  $ cat f4.bat
  rem empty\r (esc)

  $ "$PYTHON" -c 'open("f5.sh", "wb").write(b"# empty\x0D\x0A")'
  $ hg add f5.sh
  $ hg ci -m 7
  $ cat f5.sh
  # empty\r (esc)
  $ hg cat f5.sh
  # empty
  $ echo '% just linefeed' > linefeed
  $ hg ci -qAm 8 linefeed
  $ cat linefeed
  % just linefeed
  $ hg cat linefeed
  % just linefeed
  $ hg st -q
  $ hg revert -a linefeed
  no changes needed to linefeed
  $ cat linefeed
  % just linefeed
  $ hg st -q
  $ echo modified >> linefeed
  $ hg st -q
  M linefeed
  $ hg revert -a
  reverting linefeed
  $ hg st -q
  $ cat linefeed
  % just linefeed\r (esc)

  $ cd ..