view tests/test-merge-criss-cross.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

Criss cross merging

  $ hg init criss-cross
  $ cd criss-cross
  $ echo '0 base' > f1
  $ echo '0 base' > f2
  $ hg ci -Aqm '0 base'

  $ echo '1 first change' > f1
  $ hg ci -m '1 first change f1'

  $ hg up -qr0
  $ echo '2 first change' > f2
  $ mkdir d1
  $ echo '0 base' > d1/f3
  $ echo '0 base' > d1/f4
  $ hg add -q d1
  $ hg ci -qm '2 first change f2'

  $ hg merge -qr 1
  $ hg rm d1/f3
  $ hg mv -q d1 d2
  $ hg ci -m '3 merge'

  $ hg up -qr2
  $ hg merge -qr1
  $ hg ci -qm '4 merge'

  $ echo '5 second change' > f1
  $ hg ci -m '5 second change f1'

  $ hg up -r3
  2 files updated, 0 files merged, 2 files removed, 0 files unresolved
  $ echo '6 second change' > f2
  $ hg ci -m '6 second change f2'

  $ hg log -G
  @  changeset:   6:6373bbfdae1d
  |  tag:         tip
  |  parent:      3:c202c8af058d
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     6 second change f2
  |
  | o  changeset:   5:e673248094b1
  | |  user:        test
  | |  date:        Thu Jan 01 00:00:00 1970 +0000
  | |  summary:     5 second change f1
  | |
  | o    changeset:   4:177f58377c06
  | |\   parent:      2:d1d156401c1b
  | | |  parent:      1:0f6b37dbe527
  | | |  user:        test
  | | |  date:        Thu Jan 01 00:00:00 1970 +0000
  | | |  summary:     4 merge
  | | |
  o---+  changeset:   3:c202c8af058d
  | | |  parent:      2:d1d156401c1b
  |/ /   parent:      1:0f6b37dbe527
  | |    user:        test
  | |    date:        Thu Jan 01 00:00:00 1970 +0000
  | |    summary:     3 merge
  | |
  | o  changeset:   2:d1d156401c1b
  | |  parent:      0:40494bf2444c
  | |  user:        test
  | |  date:        Thu Jan 01 00:00:00 1970 +0000
  | |  summary:     2 first change f2
  | |
  o |  changeset:   1:0f6b37dbe527
  |/   user:        test
  |    date:        Thu Jan 01 00:00:00 1970 +0000
  |    summary:     1 first change f1
  |
  o  changeset:   0:40494bf2444c
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     0 base
  

  $ hg merge -v --debug --tool internal:dump 5 --config merge.preferancestor='!'
  note: using 0f6b37dbe527 as ancestor of 6373bbfdae1d and e673248094b1
        alternatively, use --config merge.preferancestor=d1d156401c1b
    searching for copies back to rev 3
    unmatched files in local:
     d2/f4
    unmatched files in other:
     d1/f3
     d1/f4
    all copies found (* = to merge, ! = divergent, % = renamed and deleted):
     src: 'd1/f4' -> dst: 'd2/f4' 
    checking for directory renames
     discovered dir src: 'd1/' -> dst: 'd2/'
     pending file src: 'd1/f3' -> dst: 'd2/f3'
     pending file src: 'd1/f4' -> dst: 'd2/f4'
  resolving manifests
   branchmerge: True, force: False, partial: False
   ancestor: 0f6b37dbe527, local: 6373bbfdae1d+, remote: e673248094b1
   preserving d2/f4 for resolve of d2/f4
   preserving f2 for resolve of f2
   f1: remote is newer -> g
  getting f1
   d2/f3: local directory rename - get from d1/f3 -> dg
  getting d1/f3 to d2/f3
   d2/f4: local directory rename, both created -> m (premerge)
   f2: versions differ -> m (premerge)
  picked tool ':dump' for f2 (binary False symlink False changedelete False)
  merging f2
  my f2@6373bbfdae1d+ other f2@e673248094b1 ancestor f2@0f6b37dbe527
   f2: versions differ -> m (merge)
  picked tool ':dump' for f2 (binary False symlink False changedelete False)
  my f2@6373bbfdae1d+ other f2@e673248094b1 ancestor f2@0f6b37dbe527
  3 files updated, 0 files merged, 0 files removed, 1 files unresolved
  use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon
  [1]

  $ f --dump --recurse *
  d2: directory with 2 files
  d2/f3:
  >>>
  0 base
  <<<
  d2/f4:
  >>>
  0 base
  <<<
  f1:
  >>>
  5 second change
  <<<
  f2:
  >>>
  6 second change
  <<<
  f2.base:
  >>>
  0 base
  <<<
  f2.local:
  >>>
  6 second change
  <<<
  f2.orig:
  >>>
  6 second change
  <<<
  f2.other:
  >>>
  2 first change
  <<<

  $ hg up -qC .
  $ hg merge -v --tool internal:dump 5 --config merge.preferancestor="null 40663881 3b08d"
  note: using 0f6b37dbe527 as ancestor of 6373bbfdae1d and e673248094b1
        alternatively, use --config merge.preferancestor=d1d156401c1b
  resolving manifests
  getting f1
  getting d1/f3 to d2/f3
  merging f2
  3 files updated, 0 files merged, 0 files removed, 1 files unresolved
  use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon
  [1]

Redo merge with merge.preferancestor="*" to enable bid merge

  $ rm f*
  $ hg up -qC .
  $ hg merge -v --debug --tool internal:dump 5 --config merge.preferancestor="*"
  note: merging 6373bbfdae1d+ and e673248094b1 using bids from ancestors 0f6b37dbe527 and d1d156401c1b
  
  calculating bids for ancestor 0f6b37dbe527
    searching for copies back to rev 3
    unmatched files in local:
     d2/f4
    unmatched files in other:
     d1/f3
     d1/f4
    all copies found (* = to merge, ! = divergent, % = renamed and deleted):
     src: 'd1/f4' -> dst: 'd2/f4' 
    checking for directory renames
     discovered dir src: 'd1/' -> dst: 'd2/'
     pending file src: 'd1/f3' -> dst: 'd2/f3'
     pending file src: 'd1/f4' -> dst: 'd2/f4'
  resolving manifests
   branchmerge: True, force: False, partial: False
   ancestor: 0f6b37dbe527, local: 6373bbfdae1d+, remote: e673248094b1
   d2/f3: local directory rename - get from d1/f3 -> dg
   d2/f4: local directory rename, both created -> m
   f1: remote is newer -> g
   f2: versions differ -> m
  
  calculating bids for ancestor d1d156401c1b
    searching for copies back to rev 3
    unmatched files in local:
     d2/f4
    all copies found (* = to merge, ! = divergent, % = renamed and deleted):
     src: 'd1/f4' -> dst: 'd2/f4' 
    checking for directory renames
     discovered dir src: 'd1/' -> dst: 'd2/'
  resolving manifests
   branchmerge: True, force: False, partial: False
   ancestor: d1d156401c1b, local: 6373bbfdae1d+, remote: e673248094b1
   f1: versions differ -> m
   f2: remote unchanged -> k
  
  auction for merging merge bids
   d2/f3: consensus for dg
   d2/f4: consensus for m
   f1: picking 'get' action
   f2: picking 'keep' action
  end of auction
  
   preserving d2/f4 for resolve of d2/f4
   f1: remote is newer -> g
  getting f1
   f2: remote unchanged -> k
   d2/f3: local directory rename - get from d1/f3 -> dg
  getting d1/f3 to d2/f3
   d2/f4: local directory rename, both created -> m (premerge)
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ f --dump --recurse *
  d2: directory with 2 files
  d2/f3:
  >>>
  0 base
  <<<
  d2/f4:
  >>>
  0 base
  <<<
  f1:
  >>>
  5 second change
  <<<
  f2:
  >>>
  6 second change
  <<<


The other way around:

  $ hg up -C -r5
  4 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ hg merge -v --debug --config merge.preferancestor="*"
  note: merging e673248094b1+ and 6373bbfdae1d using bids from ancestors 0f6b37dbe527 and d1d156401c1b
  
  calculating bids for ancestor 0f6b37dbe527
    searching for copies back to rev 3
    unmatched files in local:
     d1/f3
     d1/f4
    unmatched files in other:
     d2/f4
    all copies found (* = to merge, ! = divergent, % = renamed and deleted):
     src: 'd1/f4' -> dst: 'd2/f4' 
    checking for directory renames
     discovered dir src: 'd1/' -> dst: 'd2/'
     pending file src: 'd1/f3' -> dst: 'd2/f3'
     pending file src: 'd1/f4' -> dst: 'd2/f4'
  resolving manifests
   branchmerge: True, force: False, partial: False
   ancestor: 0f6b37dbe527, local: e673248094b1+, remote: 6373bbfdae1d
   d2/f3: remote directory rename - move from d1/f3 -> dm
   d2/f4: remote directory rename, both created -> m
   f1: remote unchanged -> k
   f2: versions differ -> m
  
  calculating bids for ancestor d1d156401c1b
    searching for copies back to rev 3
    unmatched files in other:
     d2/f4
    all copies found (* = to merge, ! = divergent, % = renamed and deleted):
     src: 'd1/f4' -> dst: 'd2/f4' 
    checking for directory renames
     discovered dir src: 'd1/' -> dst: 'd2/'
  resolving manifests
   branchmerge: True, force: False, partial: False
   ancestor: d1d156401c1b, local: e673248094b1+, remote: 6373bbfdae1d
   d1/f3: other deleted -> r
   d1/f4: other deleted -> r
   d2/f4: remote created -> g
   f1: versions differ -> m
   f2: remote is newer -> g
  
  auction for merging merge bids
   d1/f3: consensus for r
   d1/f4: consensus for r
   d2/f3: consensus for dm
   d2/f4: picking 'get' action
   f1: picking 'keep' action
   f2: picking 'get' action
  end of auction
  
   d1/f3: other deleted -> r
  removing d1/f3
   d1/f4: other deleted -> r
  removing d1/f4
   d2/f4: remote created -> g
  getting d2/f4
   f2: remote is newer -> g
  getting f2
   f1: remote unchanged -> k
  2 files updated, 0 files merged, 2 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ f --dump --recurse *
  d2: directory with 2 files
  d2/f3:
  >>>
  0 base
  <<<
  d2/f4:
  >>>
  0 base
  <<<
  f1:
  >>>
  5 second change
  <<<
  f2:
  >>>
  6 second change
  <<<

Verify how the output looks and and how verbose it is:

  $ hg up -qC
  $ hg merge
  2 files updated, 0 files merged, 2 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ hg up -qC tip
  $ hg merge -v
  note: merging 6373bbfdae1d+ and e673248094b1 using bids from ancestors 0f6b37dbe527 and d1d156401c1b
  
  calculating bids for ancestor 0f6b37dbe527
  resolving manifests
  
  calculating bids for ancestor d1d156401c1b
  resolving manifests
  
  auction for merging merge bids
   d2/f3: consensus for dg
   d2/f4: consensus for m
   f1: picking 'get' action
   f2: picking 'keep' action
  end of auction
  
  getting f1
  getting d1/f3 to d2/f3
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ hg up -qC
  $ hg merge -v --debug --config merge.preferancestor="*"
  note: merging 6373bbfdae1d+ and e673248094b1 using bids from ancestors 0f6b37dbe527 and d1d156401c1b
  
  calculating bids for ancestor 0f6b37dbe527
    searching for copies back to rev 3
    unmatched files in local:
     d2/f4
    unmatched files in other:
     d1/f3
     d1/f4
    all copies found (* = to merge, ! = divergent, % = renamed and deleted):
     src: 'd1/f4' -> dst: 'd2/f4' 
    checking for directory renames
     discovered dir src: 'd1/' -> dst: 'd2/'
     pending file src: 'd1/f3' -> dst: 'd2/f3'
     pending file src: 'd1/f4' -> dst: 'd2/f4'
  resolving manifests
   branchmerge: True, force: False, partial: False
   ancestor: 0f6b37dbe527, local: 6373bbfdae1d+, remote: e673248094b1
   d2/f3: local directory rename - get from d1/f3 -> dg
   d2/f4: local directory rename, both created -> m
   f1: remote is newer -> g
   f2: versions differ -> m
  
  calculating bids for ancestor d1d156401c1b
    searching for copies back to rev 3
    unmatched files in local:
     d2/f4
    all copies found (* = to merge, ! = divergent, % = renamed and deleted):
     src: 'd1/f4' -> dst: 'd2/f4' 
    checking for directory renames
     discovered dir src: 'd1/' -> dst: 'd2/'
  resolving manifests
   branchmerge: True, force: False, partial: False
   ancestor: d1d156401c1b, local: 6373bbfdae1d+, remote: e673248094b1
   f1: versions differ -> m
   f2: remote unchanged -> k
  
  auction for merging merge bids
   d2/f3: consensus for dg
   d2/f4: consensus for m
   f1: picking 'get' action
   f2: picking 'keep' action
  end of auction
  
   preserving d2/f4 for resolve of d2/f4
   f1: remote is newer -> g
  getting f1
   f2: remote unchanged -> k
   d2/f3: local directory rename - get from d1/f3 -> dg
  getting d1/f3 to d2/f3
   d2/f4: local directory rename, both created -> m (premerge)
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

Test the greatest common ancestor returning multiple changesets

  $ hg log -r 'heads(commonancestors(head()))'
  changeset:   1:0f6b37dbe527
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     1 first change f1
  
  changeset:   2:d1d156401c1b
  parent:      0:40494bf2444c
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     2 first change f2
  

  $ cd ..

http://stackoverflow.com/questions/9350005/how-do-i-specify-a-merge-base-to-use-in-a-hg-merge/9430810

  $ hg init ancestor-merging
  $ cd ancestor-merging
  $ echo a > x
  $ hg commit -A -m a x
  $ hg update -q 0
  $ echo b >> x
  $ hg commit -m b
  $ hg update -q 0
  $ echo c >> x
  $ hg commit -qm c
  $ hg update -q 1
  $ hg merge -q --tool internal:local 2
  $ echo c >> x
  $ hg commit -m bc
  $ hg update -q 2
  $ hg merge -q --tool internal:local 1
  $ echo b >> x
  $ hg commit -qm cb

  $ hg merge --config merge.preferancestor='!'
  note: using 70008a2163f6 as ancestor of 0d355fdef312 and 4b8b546a3eef
        alternatively, use --config merge.preferancestor=b211bbc6eb3c
  merging x
  0 files updated, 1 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ cat x
  a
  c
  b
  c

  $ hg up -qC .

  $ hg merge --config merge.preferancestor=b211bbc6eb3c
  note: using b211bbc6eb3c as ancestor of 0d355fdef312 and 4b8b546a3eef
        alternatively, use --config merge.preferancestor=70008a2163f6
  merging x
  0 files updated, 1 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ cat x
  a
  b
  c
  b

  $ hg up -qC .

  $ hg merge -v --config merge.preferancestor="*"
  note: merging 0d355fdef312+ and 4b8b546a3eef using bids from ancestors 70008a2163f6 and b211bbc6eb3c
  
  calculating bids for ancestor 70008a2163f6
  resolving manifests
  
  calculating bids for ancestor b211bbc6eb3c
  resolving manifests
  
  auction for merging merge bids
   x: multiple bids for merge action:
    versions differ -> m
    versions differ -> m
   x: ambiguous merge - picked m action
  end of auction
  
  merging x
  0 files updated, 1 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ cat x
  a
  c
  b
  c

Verify that the old context ancestor works with / despite preferancestor:

  $ hg log -r 'ancestor(head())' --config merge.preferancestor=1 -T '{rev}\n'
  1
  $ hg log -r 'ancestor(head())' --config merge.preferancestor=2 -T '{rev}\n'
  2
  $ hg log -r 'ancestor(head())' --config merge.preferancestor=3 -T '{rev}\n'
  1
  $ hg log -r 'ancestor(head())' --config merge.preferancestor='1337 * - 2' -T '{rev}\n'
  2

  $ cd ..