view tests/test-rollback.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

setup repo
  $ hg init t
  $ cd t
  $ echo a > a
  $ hg commit -Am'add a'
  adding a
  $ hg verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checked 1 changesets with 1 changes to 1 files
  $ hg parents
  changeset:   0:1f0dee641bb7
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     add a
  

rollback to null revision
  $ hg status
  $ hg rollback
  repository tip rolled back to revision -1 (undo commit)
  working directory now based on revision -1
  $ hg verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checked 0 changesets with 0 changes to 0 files
  $ hg parents
  $ hg status
  A a

Two changesets this time so we rollback to a real changeset
  $ hg commit -m'add a again'
  $ echo a >> a
  $ hg commit -m'modify a'

Test issue 902 (current branch is preserved)
  $ hg branch test
  marked working directory as branch test
  (branches are permanent and global, did you want a bookmark?)
  $ hg rollback
  repository tip rolled back to revision 0 (undo commit)
  working directory now based on revision 0
  $ hg branch
  default

Test issue 1635 (commit message saved)
  $ cat .hg/last-message.txt ; echo
  modify a

Test rollback of hg before issue 902 was fixed

  $ hg commit -m "test3"
  $ hg branch test
  marked working directory as branch test
  (branches are permanent and global, did you want a bookmark?)
  $ rm .hg/undo.branch
  $ hg rollback
  repository tip rolled back to revision 0 (undo commit)
  named branch could not be reset: current branch is still 'test'
  working directory now based on revision 0
  $ hg branch
  test

working dir unaffected by rollback: do not restore dirstate et. al.
  $ hg log --template '{rev}  {branch}  {desc|firstline}\n'
  0  default  add a again
  $ hg status
  M a
  $ hg bookmark foo
  $ hg commit -m'modify a again'
  $ echo b > b
  $ hg bookmark bar -r default #making bar active, before the transaction
  $ hg commit -Am'add b'
  adding b
  $ hg log --template '{rev}  {branch}  {desc|firstline}\n'
  2  test  add b
  1  test  modify a again
  0  default  add a again
  $ hg update bar
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (activating bookmark bar)
  $ cat .hg/undo.branch ; echo
  test
  $ hg rollback -f
  repository tip rolled back to revision 1 (undo commit)
  $ hg id -n
  0
  $ hg branch
  default
  $ cat .hg/bookmarks.current ; echo
  bar
  $ hg bookmark --delete foo bar

rollback by pretxncommit saves commit message (issue1635)

  $ echo a >> a
  $ hg --config hooks.pretxncommit=false commit -m"precious commit message"
  transaction abort!
  rollback completed
  abort: pretxncommit hook exited with status * (glob)
  [255]
  $ cat .hg/last-message.txt ; echo
  precious commit message

same thing, but run $EDITOR

  $ cat > editor.sh << '__EOF__'
  > echo "another precious commit message" > "$1"
  > __EOF__
  $ HGEDITOR="\"sh\" \"`pwd`/editor.sh\"" hg --config hooks.pretxncommit=false commit 2>&1
  note: commit message saved in .hg/last-message.txt
  transaction abort!
  rollback completed
  abort: pretxncommit hook exited with status * (glob)
  [255]
  $ cat .hg/last-message.txt
  another precious commit message

test rollback on served repository

#if serve
  $ hg commit -m "precious commit message"
  $ hg serve -p $HGPORT -d --pid-file=hg.pid -A access.log -E errors.log
  $ cat hg.pid >> $DAEMON_PIDS
  $ cd ..
  $ hg clone http://localhost:$HGPORT u
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 3 changesets with 2 changes to 1 files (+1 heads)
  new changesets 23b0221f3370:068774709090
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd u
  $ hg id default
  068774709090

now rollback and observe that 'hg serve' reloads the repository and
presents the correct tip changeset:

  $ hg -R ../t rollback
  repository tip rolled back to revision 1 (undo commit)
  working directory now based on revision 0
  $ hg id default
  791dd2169706

  $ killdaemons.py
#endif

update to older changeset and then refuse rollback, because
that would lose data (issue2998)
  $ cd ../t
  $ hg -q update
  $ rm `hg status -un`
  $ template='{rev}:{node|short}  [{branch}]  {desc|firstline}\n'
  $ echo 'valuable new file' > b
  $ echo 'valuable modification' >> a
  $ hg commit -A -m'a valuable change'
  adding b
  $ hg update 0
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ hg rollback
  abort: rollback of last commit while not checked out may lose data
  (use -f to force)
  [255]
  $ hg tip -q
  2:4d9cd3795eea
  $ hg rollback -f
  repository tip rolled back to revision 1 (undo commit)
  $ hg status
  $ hg log --removed b   # yep, it's gone

same again, but emulate an old client that doesn't write undo.desc
  $ hg -q update
  $ echo 'valuable modification redux' >> a
  $ hg commit -m'a valuable change redux'
  $ rm .hg/undo.desc
  $ hg update 0
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg rollback
  rolling back unknown transaction
  $ cat a
  a

corrupt journal test
  $ echo "foo" > .hg/store/journal
  $ hg recover
  rolling back interrupted transaction
  couldn't read journal entry 'foo\n'!
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checked 2 changesets with 2 changes to 1 files

rollback disabled by config
  $ cat >> $HGRCPATH <<EOF
  > [ui]
  > rollback = false
  > EOF
  $ echo narf >> pinky-sayings.txt
  $ hg add pinky-sayings.txt
  $ hg ci -m 'First one.'
  $ hg rollback
  abort: rollback is disabled because it is unsafe
  (see `hg help -v rollback` for information)
  [255]

  $ cd ..

I/O errors on stdio are handled properly (issue5658)

  $ cat > badui.py << EOF
  > import errno
  > from mercurial.i18n import _
  > from mercurial import (
  >     error,
  >     registrar,
  >     ui as uimod,
  > )
  > 
  > configtable = {}
  > configitem = registrar.configitem(configtable)
  > 
  > configitem(b'ui', b'ioerrors',
  >     default=list,
  > )
  > 
  > def pretxncommit(ui, repo, **kwargs):
  >     ui.warn(b'warn during pretxncommit\n')
  > 
  > def pretxnclose(ui, repo, **kwargs):
  >     ui.warn(b'warn during pretxnclose\n')
  > 
  > def txnclose(ui, repo, **kwargs):
  >     ui.warn(b'warn during txnclose\n')
  > 
  > def txnabort(ui, repo, **kwargs):
  >     ui.warn(b'warn during abort\n')
  > 
  > class fdproxy(object):
  >     def __init__(self, ui, o):
  >         self._ui = ui
  >         self._o = o
  > 
  >     def __getattr__(self, attr):
  >         return getattr(self._o, attr)
  > 
  >     def write(self, msg):
  >         errors = set(self._ui.configlist(b'ui', b'ioerrors'))
  >         pretxncommit = msg == b'warn during pretxncommit\n'
  >         pretxnclose = msg == b'warn during pretxnclose\n'
  >         txnclose = msg == b'warn during txnclose\n'
  >         txnabort = msg == b'warn during abort\n'
  >         msgabort = msg == _(b'transaction abort!\n')
  >         msgrollback = msg == _(b'rollback completed\n')
  > 
  >         if pretxncommit and b'pretxncommit' in errors:
  >             raise IOError(errno.EPIPE, 'simulated epipe')
  >         if pretxnclose and b'pretxnclose' in errors:
  >             raise IOError(errno.EIO, 'simulated eio')
  >         if txnclose and b'txnclose' in errors:
  >             raise IOError(errno.EBADF, 'simulated badf')
  >         if txnabort and b'txnabort' in errors:
  >             raise IOError(errno.EPIPE, 'simulated epipe')
  >         if msgabort and b'msgabort' in errors:
  >             raise IOError(errno.EBADF, 'simulated ebadf')
  >         if msgrollback and b'msgrollback' in errors:
  >             raise IOError(errno.EIO, 'simulated eio')
  > 
  >         return self._o.write(msg)
  > 
  > def uisetup(ui):
  >     class badui(ui.__class__):
  >         def write_err(self, *args, **kwargs):
  >             olderr = self.ferr
  >             try:
  >                 self.ferr = fdproxy(self, olderr)
  >                 return super(badui, self).write_err(*args, **kwargs)
  >             finally:
  >                 self.ferr = olderr
  > 
  >     ui.__class__ = badui
  > 
  > def reposetup(ui, repo):
  >     ui.setconfig(b'hooks', b'pretxnclose.badui', pretxnclose, b'badui')
  >     ui.setconfig(b'hooks', b'txnclose.badui', txnclose, b'badui')
  >     ui.setconfig(b'hooks', b'pretxncommit.badui', pretxncommit, b'badui')
  >     ui.setconfig(b'hooks', b'txnabort.badui', txnabort, b'badui')
  > EOF

  $ cat >> $HGRCPATH << EOF
  > [extensions]
  > badui = $TESTTMP/badui.py
  > EOF

An I/O error during pretxncommit is handled

  $ hg init ioerror-pretxncommit
  $ cd ioerror-pretxncommit
  $ echo 0 > foo
  $ hg -q commit -A -m initial
  warn during pretxncommit
  warn during pretxnclose
  warn during txnclose
  $ echo 1 > foo
  $ hg --config ui.ioerrors=pretxncommit commit -m 'error during pretxncommit'
  warn during pretxnclose
  warn during txnclose

  $ hg commit -m 'commit 1'
  nothing changed
  [1]

  $ cd ..

An I/O error during pretxnclose is handled

  $ hg init ioerror-pretxnclose
  $ cd ioerror-pretxnclose
  $ echo 0 > foo
  $ hg -q commit -A -m initial
  warn during pretxncommit
  warn during pretxnclose
  warn during txnclose

  $ echo 1 > foo
  $ hg --config ui.ioerrors=pretxnclose commit -m 'error during pretxnclose'
  warn during pretxncommit
  warn during txnclose

  $ hg commit -m 'commit 1'
  nothing changed
  [1]

  $ cd ..

An I/O error during txnclose is handled

  $ hg init ioerror-txnclose
  $ cd ioerror-txnclose
  $ echo 0 > foo
  $ hg -q commit -A -m initial
  warn during pretxncommit
  warn during pretxnclose
  warn during txnclose

  $ echo 1 > foo
  $ hg --config ui.ioerrors=txnclose commit -m 'error during txnclose'
  warn during pretxncommit
  warn during pretxnclose

  $ hg commit -m 'commit 1'
  nothing changed
  [1]

  $ cd ..

An I/O error writing "transaction abort" is handled

  $ hg init ioerror-msgabort
  $ cd ioerror-msgabort

  $ echo 0 > foo
  $ hg -q commit -A -m initial
  warn during pretxncommit
  warn during pretxnclose
  warn during txnclose

  $ echo 1 > foo
  $ hg --config ui.ioerrors=msgabort --config hooks.pretxncommit=false commit -m 'error during abort message'
  warn during abort
  rollback completed
  abort: pretxncommit hook exited with status 1
  [255]

  $ hg commit -m 'commit 1'
  warn during pretxncommit
  warn during pretxnclose
  warn during txnclose

  $ cd ..

An I/O error during txnabort should still result in rollback

  $ hg init ioerror-txnabort
  $ cd ioerror-txnabort

  $ echo 0 > foo
  $ hg -q commit -A -m initial
  warn during pretxncommit
  warn during pretxnclose
  warn during txnclose

  $ echo 1 > foo
  $ hg --config ui.ioerrors=txnabort --config hooks.pretxncommit=false commit -m 'error during abort'
  transaction abort!
  rollback completed
  abort: pretxncommit hook exited with status 1
  [255]

  $ hg commit -m 'commit 1'
  warn during pretxncommit
  warn during pretxnclose
  warn during txnclose

  $ cd ..

An I/O error writing "rollback completed" is handled

  $ hg init ioerror-msgrollback
  $ cd ioerror-msgrollback

  $ echo 0 > foo
  $ hg -q commit -A -m initial
  warn during pretxncommit
  warn during pretxnclose
  warn during txnclose

  $ echo 1 > foo

  $ hg --config ui.ioerrors=msgrollback --config hooks.pretxncommit=false commit -m 'error during rollback message'
  transaction abort!
  warn during abort
  abort: pretxncommit hook exited with status 1
  [255]

  $ hg verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checked 1 changesets with 1 changes to 1 files

  $ cd ..

Multiple I/O errors after transaction open are handled.
This is effectively what happens if a peer disconnects in the middle
of a transaction.

  $ hg init ioerror-multiple
  $ cd ioerror-multiple
  $ echo 0 > foo
  $ hg -q commit -A -m initial
  warn during pretxncommit
  warn during pretxnclose
  warn during txnclose

  $ echo 1 > foo

  $ hg --config ui.ioerrors=pretxncommit,pretxnclose,txnclose,txnabort,msgabort,msgrollback commit -m 'multiple errors'

  $ hg verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checked 2 changesets with 2 changes to 1 files

  $ cd ..