view tests/test-obshistory.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

This test file test the various messages when accessing obsolete
revisions.

Global setup
============

  $ . $TESTDIR/testlib/obsmarker-common.sh
  $ cat >> $HGRCPATH <<EOF
  > [ui]
  > interactive = true
  > [phases]
  > publish=False
  > [experimental]
  > evolution.createmarkers = yes
  > evolution.effect-flags = yes
  > EOF

Test output on amended commit
=============================

Test setup
----------

  $ hg init $TESTTMP/local-amend
  $ cd $TESTTMP/local-amend
  $ mkcommit ROOT
  $ mkcommit A0
  $ echo 42 >> A0
  $ hg commit --amend -m "A1
  > 
  > Better commit message"
  $ hg log --hidden -G
  @  changeset:   2:4ae3a4151de9
  |  tag:         tip
  |  parent:      0:ea207398892e
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     A1
  |
  | x  changeset:   1:471f378eab4c
  |/   user:        test
  |    date:        Thu Jan 01 00:00:00 1970 +0000
  |    obsolete:    rewritten using amend as 2:4ae3a4151de9
  |    summary:     A0
  |
  o  changeset:   0:ea207398892e
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     ROOT
  
Actual test
-----------
  $ hg update 471f378eab4c
  abort: hidden revision '471f378eab4c' was rewritten as: 4ae3a4151de9!
  (use --hidden to access hidden revisions)
  [255]
  $ hg update --hidden "desc(A0)"
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  updated to hidden changeset 471f378eab4c
  (hidden revision '471f378eab4c' was rewritten as: 4ae3a4151de9)

Test output with pruned commit
==============================

Test setup
----------

  $ hg init $TESTTMP/local-prune
  $ cd $TESTTMP/local-prune
  $ mkcommit ROOT
  $ mkcommit A0 # 0
  $ mkcommit B0 # 1
  $ hg log --hidden -G
  @  changeset:   2:0dec01379d3b
  |  tag:         tip
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     B0
  |
  o  changeset:   1:471f378eab4c
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     A0
  |
  o  changeset:   0:ea207398892e
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     ROOT
  
  $ hg debugobsolete --record-parents `getid 'desc(B0)'`
  obsoleted 1 changesets

  $ hg log --hidden -G
  @  changeset:   2:0dec01379d3b
  |  tag:         tip
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  obsolete:    pruned
  |  summary:     B0
  |
  o  changeset:   1:471f378eab4c
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     A0
  |
  o  changeset:   0:ea207398892e
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     ROOT
  

Actual test
-----------
  $ hg up 1
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ hg up 0dec01379d3b
  abort: hidden revision '0dec01379d3b' is pruned!
  (use --hidden to access hidden revisions)
  [255]
  $ hg up --hidden -r 'desc(B0)'
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  updated to hidden changeset 0dec01379d3b
  (hidden revision '0dec01379d3b' is pruned)

Test output with splitted commit
================================

Test setup
----------

  $ hg init $TESTTMP/local-split
  $ cd $TESTTMP/local-split
  $ mkcommit ROOT
  $ echo 42 >> a
  $ echo 43 >> b
  $ hg commit -A -m "A0"
  adding a
  adding b
  $ hg log --hidden -G
  @  changeset:   1:471597cad322
  |  tag:         tip
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     A0
  |
  o  changeset:   0:ea207398892e
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     ROOT
  
# Simulate a split
  $ hg up 0
  0 files updated, 0 files merged, 2 files removed, 0 files unresolved

  $ echo 42 >> a
  $ hg commit -A -m "A0"
  adding a
  created new head

  $ echo 43 >> b
  $ hg commit -A -m "A0"
  adding b

  $ hg debugobsolete `getid '1'` `getid '2'` `getid '3'`
  obsoleted 1 changesets

  $ hg log --hidden -G
  @  changeset:   3:f257fde29c7a
  |  tag:         tip
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     A0
  |
  o  changeset:   2:337fec4d2edc
  |  parent:      0:ea207398892e
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     A0
  |
  | x  changeset:   1:471597cad322
  |/   user:        test
  |    date:        Thu Jan 01 00:00:00 1970 +0000
  |    obsolete:    split as 2:337fec4d2edc, 3:f257fde29c7a
  |    summary:     A0
  |
  o  changeset:   0:ea207398892e
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     ROOT
  
Actual test
-----------
  $ hg update 471597cad322
  abort: hidden revision '471597cad322' was split as: 337fec4d2edc, f257fde29c7a!
  (use --hidden to access hidden revisions)
  [255]
  $ hg update --hidden 'min(desc(A0))'
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  updated to hidden changeset 471597cad322
  (hidden revision '471597cad322' was split as: 337fec4d2edc, f257fde29c7a)

Test output with lots of splitted commit
========================================

Test setup
----------

  $ hg init $TESTTMP/local-lots-split
  $ cd $TESTTMP/local-lots-split
  $ mkcommit ROOT
  $ echo 42 >> a
  $ echo 43 >> b
  $ echo 44 >> c
  $ echo 45 >> d
  $ hg commit -A -m "A0"
  adding a
  adding b
  adding c
  adding d
  $ hg log --hidden -G
  @  changeset:   1:de7290d8b885
  |  tag:         tip
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     A0
  |
  o  changeset:   0:ea207398892e
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     ROOT
  
# Simulate a split
  $ hg up 0
  0 files updated, 0 files merged, 4 files removed, 0 files unresolved

  $ echo 42 >> a
  $ hg commit -A -m "A0"
  adding a
  created new head

  $ echo 43 >> b
  $ hg commit -A -m "A0"
  adding b

  $ echo 44 >> c
  $ hg commit -A -m "A0"
  adding c

  $ echo 45 >> d
  $ hg commit -A -m "A0"
  adding d

  $ hg debugobsolete `getid '1'` `getid '2'` `getid '3'` `getid '4'` `getid '5'`
  obsoleted 1 changesets

  $ hg log --hidden -G
  @  changeset:   5:c7f044602e9b
  |  tag:         tip
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     A0
  |
  o  changeset:   4:1ae8bc733a14
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     A0
  |
  o  changeset:   3:f257fde29c7a
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     A0
  |
  o  changeset:   2:337fec4d2edc
  |  parent:      0:ea207398892e
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     A0
  |
  | x  changeset:   1:de7290d8b885
  |/   user:        test
  |    date:        Thu Jan 01 00:00:00 1970 +0000
  |    obsolete:    split as 2:337fec4d2edc, 3:f257fde29c7a, 4:1ae8bc733a14, 5:c7f044602e9b
  |    summary:     A0
  |
  o  changeset:   0:ea207398892e
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     ROOT
  
Actual test
-----------
  $ hg update de7290d8b885
  abort: hidden revision 'de7290d8b885' was split as: 337fec4d2edc, f257fde29c7a and 2 more!
  (use --hidden to access hidden revisions)
  [255]
  $ hg update --hidden 'min(desc(A0))'
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  updated to hidden changeset de7290d8b885
  (hidden revision 'de7290d8b885' was split as: 337fec4d2edc, f257fde29c7a and 2 more)

Test output with folded commit
==============================

Test setup
----------

  $ hg init $TESTTMP/local-fold
  $ cd $TESTTMP/local-fold
  $ mkcommit ROOT
  $ mkcommit A0
  $ mkcommit B0
  $ hg log --hidden -G
  @  changeset:   2:0dec01379d3b
  |  tag:         tip
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     B0
  |
  o  changeset:   1:471f378eab4c
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     A0
  |
  o  changeset:   0:ea207398892e
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     ROOT
  
# Simulate a fold
  $ hg up 0
  0 files updated, 0 files merged, 2 files removed, 0 files unresolved
  $ echo "A0" > A0
  $ echo "B0" > B0
  $ hg add A0 B0
  $ hg commit -m "C0"
  created new head

  $ hg debugobsolete `getid 'desc(A0)'` `getid 'desc(C0)'`
  obsoleted 1 changesets
  1 new orphan changesets
  $ hg debugobsolete `getid 'desc(B0)'` `getid 'desc(C0)'`
  obsoleted 1 changesets

  $ hg log --hidden -G
  @  changeset:   3:eb5a0daa2192
  |  tag:         tip
  |  parent:      0:ea207398892e
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     C0
  |
  | x  changeset:   2:0dec01379d3b
  | |  user:        test
  | |  date:        Thu Jan 01 00:00:00 1970 +0000
  | |  obsolete:    rewritten as 3:eb5a0daa2192
  | |  summary:     B0
  | |
  | x  changeset:   1:471f378eab4c
  |/   user:        test
  |    date:        Thu Jan 01 00:00:00 1970 +0000
  |    obsolete:    rewritten as 3:eb5a0daa2192
  |    summary:     A0
  |
  o  changeset:   0:ea207398892e
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     ROOT
  
 Actual test
 -----------
  $ hg update 471f378eab4c
  abort: hidden revision '471f378eab4c' was rewritten as: eb5a0daa2192!
  (use --hidden to access hidden revisions)
  [255]
  $ hg update --hidden 'desc(A0)'
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  updated to hidden changeset 471f378eab4c
  (hidden revision '471f378eab4c' was rewritten as: eb5a0daa2192)
  $ hg update 0dec01379d3b
  abort: hidden revision '0dec01379d3b' was rewritten as: eb5a0daa2192!
  (use --hidden to access hidden revisions)
  [255]
  $ hg update --hidden 'desc(B0)'
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  updated to hidden changeset 0dec01379d3b
  (hidden revision '0dec01379d3b' was rewritten as: eb5a0daa2192)

Test output with divergence
===========================

Test setup
----------

  $ hg init $TESTTMP/local-divergence
  $ cd $TESTTMP/local-divergence
  $ mkcommit ROOT
  $ mkcommit A0
  $ hg commit --amend -m "A1"
  $ hg log --hidden -G
  @  changeset:   2:fdf9bde5129a
  |  tag:         tip
  |  parent:      0:ea207398892e
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     A1
  |
  | x  changeset:   1:471f378eab4c
  |/   user:        test
  |    date:        Thu Jan 01 00:00:00 1970 +0000
  |    obsolete:    rewritten using amend as 2:fdf9bde5129a
  |    summary:     A0
  |
  o  changeset:   0:ea207398892e
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     ROOT
  
  $ hg update --hidden 'desc(A0)'
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  updated to hidden changeset 471f378eab4c
  (hidden revision '471f378eab4c' was rewritten as: fdf9bde5129a)
  $ hg commit --amend -m "A2"
  2 new content-divergent changesets
  $ hg log --hidden -G
  @  changeset:   3:65b757b745b9
  |  tag:         tip
  |  parent:      0:ea207398892e
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  instability: content-divergent
  |  summary:     A2
  |
  | *  changeset:   2:fdf9bde5129a
  |/   parent:      0:ea207398892e
  |    user:        test
  |    date:        Thu Jan 01 00:00:00 1970 +0000
  |    instability: content-divergent
  |    summary:     A1
  |
  | x  changeset:   1:471f378eab4c
  |/   user:        test
  |    date:        Thu Jan 01 00:00:00 1970 +0000
  |    obsolete:    rewritten using amend as 2:fdf9bde5129a
  |    obsolete:    rewritten using amend as 3:65b757b745b9
  |    summary:     A0
  |
  o  changeset:   0:ea207398892e
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     ROOT
  
Actual test
-----------
  $ hg update 471f378eab4c
  abort: hidden revision '471f378eab4c' has diverged!
  (use --hidden to access hidden revisions)
  [255]
  $ hg update --hidden 'desc(A0)'
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  updated to hidden changeset 471f378eab4c
  (hidden revision '471f378eab4c' has diverged)

Test output with amended + folded commit
========================================

Test setup
----------

  $ hg init $TESTTMP/local-amend-fold
  $ cd $TESTTMP/local-amend-fold
  $ mkcommit ROOT
  $ mkcommit A0
  $ mkcommit B0
  $ hg commit --amend -m "B1"
  $ hg log --hidden -G
  @  changeset:   3:b7ea6d14e664
  |  tag:         tip
  |  parent:      1:471f378eab4c
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     B1
  |
  | x  changeset:   2:0dec01379d3b
  |/   user:        test
  |    date:        Thu Jan 01 00:00:00 1970 +0000
  |    obsolete:    rewritten using amend as 3:b7ea6d14e664
  |    summary:     B0
  |
  o  changeset:   1:471f378eab4c
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     A0
  |
  o  changeset:   0:ea207398892e
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     ROOT
  

# Simulate a fold
  $ hg up 0
  0 files updated, 0 files merged, 2 files removed, 0 files unresolved
  $ echo "A0" > A0
  $ echo "B0" > B0
  $ hg add A0 B0
  $ hg commit -m "C0"
  created new head

  $ hg debugobsolete `getid 'desc(A0)'` `getid 'desc(C0)'`
  obsoleted 1 changesets
  1 new orphan changesets
  $ hg debugobsolete `getid 'desc(B1)'` `getid 'desc(C0)'`
  obsoleted 1 changesets

  $ hg log --hidden -G
  @  changeset:   4:eb5a0daa2192
  |  tag:         tip
  |  parent:      0:ea207398892e
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     C0
  |
  | x  changeset:   3:b7ea6d14e664
  | |  parent:      1:471f378eab4c
  | |  user:        test
  | |  date:        Thu Jan 01 00:00:00 1970 +0000
  | |  obsolete:    rewritten as 4:eb5a0daa2192
  | |  summary:     B1
  | |
  | | x  changeset:   2:0dec01379d3b
  | |/   user:        test
  | |    date:        Thu Jan 01 00:00:00 1970 +0000
  | |    obsolete:    rewritten using amend as 3:b7ea6d14e664
  | |    summary:     B0
  | |
  | x  changeset:   1:471f378eab4c
  |/   user:        test
  |    date:        Thu Jan 01 00:00:00 1970 +0000
  |    obsolete:    rewritten as 4:eb5a0daa2192
  |    summary:     A0
  |
  o  changeset:   0:ea207398892e
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     ROOT
  
 Actual test
 -----------
  $ hg update 471f378eab4c
  abort: hidden revision '471f378eab4c' was rewritten as: eb5a0daa2192!
  (use --hidden to access hidden revisions)
  [255]
  $ hg update --hidden 'desc(A0)'
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  updated to hidden changeset 471f378eab4c
  (hidden revision '471f378eab4c' was rewritten as: eb5a0daa2192)
  $ hg update --hidden 0dec01379d3b
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  updated to hidden changeset 0dec01379d3b
  (hidden revision '0dec01379d3b' was rewritten as: eb5a0daa2192)
  $ hg update 0dec01379d3b
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg update --hidden 'desc(B0)'
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved