view tests/test-rebase-named-branches.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]
  > rebase=
  > 
  > [phases]
  > publish=False
  > 
  > [alias]
  > tglog = log -G --template "{rev}: {node|short} '{desc}' {branches}\n"
  > EOF

  $ hg init a
  $ cd a
  $ hg unbundle "$TESTDIR/bundles/rebase.hg"
  adding changesets
  adding manifests
  adding file changes
  added 8 changesets with 7 changes to 7 files (+2 heads)
  new changesets cd010b8cd998:02de42196ebe (8 drafts)
  (run 'hg heads' to see heads, 'hg merge' to merge)
  $ hg up tip
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd ..

  $ hg clone -q -u . a a1

  $ cd a1

  $ hg update 3
  3 files updated, 0 files merged, 2 files removed, 0 files unresolved
  $ hg branch dev-one
  marked working directory as branch dev-one
  (branches are permanent and global, did you want a bookmark?)
  $ hg ci -m 'dev-one named branch'

  $ hg update 7
  2 files updated, 0 files merged, 3 files removed, 0 files unresolved
  $ hg branch dev-two
  marked working directory as branch dev-two

  $ echo x > x

  $ hg add x

  $ hg ci -m 'dev-two named branch'

  $ hg tglog
  @  9: cb039b7cae8e 'dev-two named branch' dev-two
  |
  | o  8: 643fc9128048 'dev-one named branch' dev-one
  | |
  o |  7: 02de42196ebe 'H'
  | |
  +---o  6: eea13746799a 'G'
  | | |
  o | |  5: 24b6387c8c8c 'F'
  | | |
  +---o  4: 9520eea781bc 'E'
  | |
  | o  3: 32af7686d403 'D'
  | |
  | o  2: 5fddd98957c8 'C'
  | |
  | o  1: 42ccdea3bb16 'B'
  |/
  o  0: cd010b8cd998 'A'
  

Branch name containing a dash (issue3181)

  $ hg rebase -b dev-two -d dev-one --keepbranches
  rebasing 5:24b6387c8c8c "F"
  rebasing 6:eea13746799a "G"
  rebasing 7:02de42196ebe "H"
  rebasing 9:cb039b7cae8e "dev-two named branch" (tip)
  saved backup bundle to $TESTTMP/a1/.hg/strip-backup/24b6387c8c8c-24cb8001-rebase.hg

  $ hg tglog
  @  9: 9e70cd31750f 'dev-two named branch' dev-two
  |
  o  8: 31d0e4ba75e6 'H'
  |
  | o  7: 4b988a958030 'G'
  |/|
  o |  6: 24de4aff8e28 'F'
  | |
  o |  5: 643fc9128048 'dev-one named branch' dev-one
  | |
  | o  4: 9520eea781bc 'E'
  | |
  o |  3: 32af7686d403 'D'
  | |
  o |  2: 5fddd98957c8 'C'
  | |
  o |  1: 42ccdea3bb16 'B'
  |/
  o  0: cd010b8cd998 'A'
  
  $ hg rebase -s dev-one -d 0 --keepbranches
  rebasing 5:643fc9128048 "dev-one named branch"
  rebasing 6:24de4aff8e28 "F"
  rebasing 7:4b988a958030 "G"
  rebasing 8:31d0e4ba75e6 "H"
  rebasing 9:9e70cd31750f "dev-two named branch" (tip)
  saved backup bundle to $TESTTMP/a1/.hg/strip-backup/643fc9128048-c4ee9ef5-rebase.hg

  $ hg tglog
  @  9: 59c2e59309fe 'dev-two named branch' dev-two
  |
  o  8: 904590360559 'H'
  |
  | o  7: 1a1e6f72ec38 'G'
  |/|
  o |  6: 42aa3cf0fa7a 'F'
  | |
  o |  5: bc8139ee757c 'dev-one named branch' dev-one
  | |
  | o  4: 9520eea781bc 'E'
  |/
  | o  3: 32af7686d403 'D'
  | |
  | o  2: 5fddd98957c8 'C'
  | |
  | o  1: 42ccdea3bb16 'B'
  |/
  o  0: cd010b8cd998 'A'
  
  $ hg update 3
  3 files updated, 0 files merged, 3 files removed, 0 files unresolved
  $ hg branch -f dev-one
  marked working directory as branch dev-one
  $ hg ci -m 'dev-one named branch'
  created new head

  $ hg tglog
  @  10: 643fc9128048 'dev-one named branch' dev-one
  |
  | o  9: 59c2e59309fe 'dev-two named branch' dev-two
  | |
  | o  8: 904590360559 'H'
  | |
  | | o  7: 1a1e6f72ec38 'G'
  | |/|
  | o |  6: 42aa3cf0fa7a 'F'
  | | |
  | o |  5: bc8139ee757c 'dev-one named branch' dev-one
  | | |
  | | o  4: 9520eea781bc 'E'
  | |/
  o |  3: 32af7686d403 'D'
  | |
  o |  2: 5fddd98957c8 'C'
  | |
  o |  1: 42ccdea3bb16 'B'
  |/
  o  0: cd010b8cd998 'A'
  
  $ hg rebase -b 'max(branch("dev-two"))' -d dev-one --keepbranches
  rebasing 5:bc8139ee757c "dev-one named branch"
  note: rebase of 5:bc8139ee757c created no changes to commit
  rebasing 6:42aa3cf0fa7a "F"
  rebasing 7:1a1e6f72ec38 "G"
  rebasing 8:904590360559 "H"
  rebasing 9:59c2e59309fe "dev-two named branch"
  saved backup bundle to $TESTTMP/a1/.hg/strip-backup/bc8139ee757c-f11c1080-rebase.hg

  $ hg tglog
  o  9: 71325f8bc082 'dev-two named branch' dev-two
  |
  o  8: 12b2bc666e20 'H'
  |
  | o  7: 549f007a9f5f 'G'
  |/|
  o |  6: 679f28760620 'F'
  | |
  @ |  5: 643fc9128048 'dev-one named branch' dev-one
  | |
  | o  4: 9520eea781bc 'E'
  | |
  o |  3: 32af7686d403 'D'
  | |
  o |  2: 5fddd98957c8 'C'
  | |
  o |  1: 42ccdea3bb16 'B'
  |/
  o  0: cd010b8cd998 'A'
  
  $ hg rebase -s 'max(branch("dev-one"))' -d 0 --keepbranches
  rebasing 5:643fc9128048 "dev-one named branch"
  rebasing 6:679f28760620 "F"
  rebasing 7:549f007a9f5f "G"
  rebasing 8:12b2bc666e20 "H"
  rebasing 9:71325f8bc082 "dev-two named branch" (tip)
  saved backup bundle to $TESTTMP/a1/.hg/strip-backup/643fc9128048-6cdd1a52-rebase.hg

  $ hg tglog
  o  9: 3944801ae4ea 'dev-two named branch' dev-two
  |
  o  8: 8e279d293175 'H'
  |
  | o  7: aeefee77ab01 'G'
  |/|
  o |  6: e908b85f3729 'F'
  | |
  @ |  5: bc8139ee757c 'dev-one named branch' dev-one
  | |
  | o  4: 9520eea781bc 'E'
  |/
  | o  3: 32af7686d403 'D'
  | |
  | o  2: 5fddd98957c8 'C'
  | |
  | o  1: 42ccdea3bb16 'B'
  |/
  o  0: cd010b8cd998 'A'
  
  $ hg up -r 0 > /dev/null

Rebasing descendant onto ancestor across different named branches

  $ hg rebase -s 1 -d 9 --keepbranches
  rebasing 1:42ccdea3bb16 "B"
  rebasing 2:5fddd98957c8 "C"
  rebasing 3:32af7686d403 "D"
  saved backup bundle to $TESTTMP/a1/.hg/strip-backup/42ccdea3bb16-3cb021d3-rebase.hg

  $ hg tglog
  o  9: e9f862ce8bad 'D'
  |
  o  8: a0d543090fa4 'C'
  |
  o  7: 3bdb949809d9 'B'
  |
  o  6: 3944801ae4ea 'dev-two named branch' dev-two
  |
  o  5: 8e279d293175 'H'
  |
  | o  4: aeefee77ab01 'G'
  |/|
  o |  3: e908b85f3729 'F'
  | |
  o |  2: bc8139ee757c 'dev-one named branch' dev-one
  | |
  | o  1: 9520eea781bc 'E'
  |/
  @  0: cd010b8cd998 'A'
  
  $ hg rebase -s 5 -d 6
  abort: source and destination form a cycle
  [255]

  $ hg rebase -s 6 -d 5
  rebasing 6:3944801ae4ea "dev-two named branch"
  rebasing 7:3bdb949809d9 "B"
  rebasing 8:a0d543090fa4 "C"
  rebasing 9:e9f862ce8bad "D" (tip)
  saved backup bundle to $TESTTMP/a1/.hg/strip-backup/3944801ae4ea-fb46ed74-rebase.hg

  $ hg tglog
  o  9: e522577ccdbd 'D'
  |
  o  8: 810110211f50 'C'
  |
  o  7: 160b0930ccc6 'B'
  |
  o  6: c57724c84928 'dev-two named branch'
  |
  o  5: 8e279d293175 'H'
  |
  | o  4: aeefee77ab01 'G'
  |/|
  o |  3: e908b85f3729 'F'
  | |
  o |  2: bc8139ee757c 'dev-one named branch' dev-one
  | |
  | o  1: 9520eea781bc 'E'
  |/
  @  0: cd010b8cd998 'A'
  

Reopen branch by rebase

  $ hg up -qr3
  $ hg branch -q b
  $ hg ci -m 'create b'
  $ hg ci -m 'close b' --close
  $ hg rebase -b 8 -d b
  reopening closed branch head 2b586e70108d
  rebasing 5:8e279d293175 "H"
  rebasing 6:c57724c84928 "dev-two named branch"
  rebasing 7:160b0930ccc6 "B"
  rebasing 8:810110211f50 "C"
  rebasing 9:e522577ccdbd "D"
  saved backup bundle to $TESTTMP/a1/.hg/strip-backup/8e279d293175-b023e27c-rebase.hg

  $ cd ..

Rebase to other head on branch

Set up a case:

  $ hg init case1
  $ cd case1
  $ touch f
  $ hg ci -qAm0
  $ hg branch -q b
  $ echo >> f
  $ hg ci -qAm 'b1'
  $ hg up -qr -2
  $ hg branch -qf b
  $ hg ci -qm 'b2'
  $ hg up -qr -3
  $ hg branch -q c
  $ hg ci -m 'c1'

  $ hg tglog
  @  3: c062e3ecd6c6 'c1' c
  |
  | o  2: 792845bb77ee 'b2' b
  |/
  | o  1: 40039acb7ca5 'b1' b
  |/
  o  0: d681519c3ea7 '0'
  
  $ hg clone -q . ../case2

rebase 'b2' to another lower branch head

  $ hg up -qr 2
  $ hg rebase
  rebasing 2:792845bb77ee "b2"
  note: rebase of 2:792845bb77ee created no changes to commit
  saved backup bundle to $TESTTMP/case1/.hg/strip-backup/792845bb77ee-627120ee-rebase.hg
  $ hg tglog
  o  2: c062e3ecd6c6 'c1' c
  |
  | @  1: 40039acb7ca5 'b1' b
  |/
  o  0: d681519c3ea7 '0'
  

rebase 'b1' on top of the tip of the branch ('b2') - ignoring the tip branch ('c1')

  $ cd ../case2
  $ hg up -qr 1
  $ hg rebase
  rebasing 1:40039acb7ca5 "b1"
  saved backup bundle to $TESTTMP/case2/.hg/strip-backup/40039acb7ca5-342b72d1-rebase.hg
  $ hg tglog
  @  3: 76abc1c6f8c7 'b1' b
  |
  | o  2: c062e3ecd6c6 'c1' c
  | |
  o |  1: 792845bb77ee 'b2' b
  |/
  o  0: d681519c3ea7 '0'
  

rebase 'c1' to the branch head 'c2' that is closed

  $ hg branch -qf c
  $ hg ci -qm 'c2 closed' --close
  $ hg up -qr 2
  $ hg tglog
  _  4: 8427af5d86f2 'c2 closed' c
  |
  o  3: 76abc1c6f8c7 'b1' b
  |
  | @  2: c062e3ecd6c6 'c1' c
  | |
  o |  1: 792845bb77ee 'b2' b
  |/
  o  0: d681519c3ea7 '0'
  
  $ hg rebase
  abort: branch 'c' has one head - please rebase to an explicit rev
  (run 'hg heads' to see all heads)
  [255]
  $ hg tglog
  _  4: 8427af5d86f2 'c2 closed' c
  |
  o  3: 76abc1c6f8c7 'b1' b
  |
  | @  2: c062e3ecd6c6 'c1' c
  | |
  o |  1: 792845bb77ee 'b2' b
  |/
  o  0: d681519c3ea7 '0'
  

  $ hg up -cr 1
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg branch x
  marked working directory as branch x
  $ hg rebase -r 3:: -d .
  rebasing 3:76abc1c6f8c7 "b1"
  rebasing 4:8427af5d86f2 "c2 closed" (tip)
  note: rebase of 4:8427af5d86f2 created no changes to commit
  saved backup bundle to $TESTTMP/case2/.hg/strip-backup/76abc1c6f8c7-cd698d13-rebase.hg
  $ hg tglog
  o  3: 117b0ed08075 'b1' x
  |
  | o  2: c062e3ecd6c6 'c1' c
  | |
  @ |  1: 792845bb77ee 'b2' b
  |/
  o  0: d681519c3ea7 '0'
  

  $ cd ..