view tests/test-unamend.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

Test for command `hg unamend` which lives in uncommit extension
===============================================================

  $ cat >> $HGRCPATH << EOF
  > [alias]
  > glog = log -G -T '{rev}:{node|short}  {desc}'
  > [experimental]
  > evolution = createmarkers, allowunstable
  > [extensions]
  > rebase =
  > amend =
  > uncommit =
  > EOF

Repo Setup

  $ hg init repo
  $ cd repo
  $ for ch in a b c d e f g h; do touch $ch; echo "foo" >> $ch; hg ci -Aqm "Added "$ch; done

  $ hg glog
  @  7:ec2426147f0e  Added h
  |
  o  6:87d6d6676308  Added g
  |
  o  5:825660c69f0c  Added f
  |
  o  4:aa98ab95a928  Added e
  |
  o  3:62615734edd5  Added d
  |
  o  2:28ad74487de9  Added c
  |
  o  1:29becc82797a  Added b
  |
  o  0:18d04c59bb5d  Added a
  
Trying to unamend when there was no amend done

  $ hg unamend
  abort: changeset must have one predecessor, found 0 predecessors
  [255]

Unamend on clean wdir and tip

  $ echo "bar" >> h
  $ hg amend

  $ hg exp
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID c9fa1a715c1b7661c0fafb362a9f30bd75878d7d
  # Parent  87d6d66763085b629e6d7ed56778c79827273022
  Added h
  
  diff -r 87d6d6676308 -r c9fa1a715c1b h
  --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
  +++ b/h	Thu Jan 01 00:00:00 1970 +0000
  @@ -0,0 +1,2 @@
  +foo
  +bar

  $ hg glog --hidden
  @  8:c9fa1a715c1b  Added h
  |
  | x  7:ec2426147f0e  Added h
  |/
  o  6:87d6d6676308  Added g
  |
  o  5:825660c69f0c  Added f
  |
  o  4:aa98ab95a928  Added e
  |
  o  3:62615734edd5  Added d
  |
  o  2:28ad74487de9  Added c
  |
  o  1:29becc82797a  Added b
  |
  o  0:18d04c59bb5d  Added a
  
  $ hg unamend
  $ hg glog --hidden
  @  9:46d02d47eec6  Added h
  |
  | x  8:c9fa1a715c1b  Added h
  |/
  | x  7:ec2426147f0e  Added h
  |/
  o  6:87d6d6676308  Added g
  |
  o  5:825660c69f0c  Added f
  |
  o  4:aa98ab95a928  Added e
  |
  o  3:62615734edd5  Added d
  |
  o  2:28ad74487de9  Added c
  |
  o  1:29becc82797a  Added b
  |
  o  0:18d04c59bb5d  Added a
  
  $ hg diff
  diff -r 46d02d47eec6 h
  --- a/h	Thu Jan 01 00:00:00 1970 +0000
  +++ b/h	Thu Jan 01 00:00:00 1970 +0000
  @@ -1,1 +1,2 @@
   foo
  +bar

  $ hg exp
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID 46d02d47eec6ca096b8dcab3f8f5579c40c3dd9a
  # Parent  87d6d66763085b629e6d7ed56778c79827273022
  Added h
  
  diff -r 87d6d6676308 -r 46d02d47eec6 h
  --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
  +++ b/h	Thu Jan 01 00:00:00 1970 +0000
  @@ -0,0 +1,1 @@
  +foo

  $ hg status
  M h

  $ hg log -r . -T '{extras % "{extra}\n"}' --config alias.log=log
  branch=default
  unamend_source=c9fa1a715c1b7661c0fafb362a9f30bd75878d7d

Using unamend to undo an unamed (intentional)

  $ hg unamend
  $ hg exp
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID 850ddfc1bc662997ec6094ada958f01f0cc8070a
  # Parent  87d6d66763085b629e6d7ed56778c79827273022
  Added h
  
  diff -r 87d6d6676308 -r 850ddfc1bc66 h
  --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
  +++ b/h	Thu Jan 01 00:00:00 1970 +0000
  @@ -0,0 +1,2 @@
  +foo
  +bar
  $ hg diff

Unamend on a dirty working directory

  $ echo "bar" >> a
  $ hg amend
  $ echo "foobar" >> a
  $ echo "bar" >> b
  $ hg status
  M a
  M b

  $ hg unamend

  $ hg status
  M a
  M b

  $ hg diff
  diff -r ec338db45d51 a
  --- a/a	Thu Jan 01 00:00:00 1970 +0000
  +++ b/a	Thu Jan 01 00:00:00 1970 +0000
  @@ -1,1 +1,3 @@
   foo
  +bar
  +foobar
  diff -r ec338db45d51 b
  --- a/b	Thu Jan 01 00:00:00 1970 +0000
  +++ b/b	Thu Jan 01 00:00:00 1970 +0000
  @@ -1,1 +1,2 @@
   foo
  +bar

Unamending an added file

  $ hg ci -m "Added things to a and b"
  $ echo foo > bar
  $ hg add bar
  $ hg amend

  $ hg unamend
  $ hg status
  A bar

  $ hg revert --all
  forgetting bar

Unamending a removed file

  $ hg remove a
  $ hg amend

  $ hg unamend
  $ hg status
  R a
  ? bar

  $ hg revert --all
  undeleting a

Unamending an added file with dirty wdir status

  $ hg add bar
  $ hg amend
  $ echo bar >> bar
  $ hg status
  M bar

  $ hg unamend
  $ hg status
  A bar
  $ hg diff
  diff -r 7f79409af972 bar
  --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
  +++ b/bar	Thu Jan 01 00:00:00 1970 +0000
  @@ -0,0 +1,2 @@
  +foo
  +bar

  $ hg revert --all
  forgetting bar

Unamending in middle of a stack

  $ hg glog
  @  19:7f79409af972  Added things to a and b
  |
  o  12:ec338db45d51  Added h
  |
  o  6:87d6d6676308  Added g
  |
  o  5:825660c69f0c  Added f
  |
  o  4:aa98ab95a928  Added e
  |
  o  3:62615734edd5  Added d
  |
  o  2:28ad74487de9  Added c
  |
  o  1:29becc82797a  Added b
  |
  o  0:18d04c59bb5d  Added a
  
  $ hg up 5
  2 files updated, 0 files merged, 2 files removed, 0 files unresolved
  $ echo bar >> f
  $ hg amend
  3 new orphan changesets
  $ hg rebase -s 6 -d . -q

  $ hg glog
  o  23:03ddd6fc5af1  Added things to a and b
  |
  o  22:3e7b64ee157b  Added h
  |
  o  21:49635b68477e  Added g
  |
  @  20:93f0e8ffab32  Added f
  |
  o  4:aa98ab95a928  Added e
  |
  o  3:62615734edd5  Added d
  |
  o  2:28ad74487de9  Added c
  |
  o  1:29becc82797a  Added b
  |
  o  0:18d04c59bb5d  Added a
  

  $ hg --config experimental.evolution=createmarkers unamend
  abort: cannot unamend changeset with children
  [255]

  $ hg unamend
  3 new orphan changesets

Trying to unamend a public changeset

  $ hg up -C 23
  5 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg phase -r . -p
  1 new phase-divergent changesets
  $ hg unamend
  abort: cannot unamend public changesets
  (see 'hg help phases' for details)
  [255]

Testing whether unamend retains copies or not

  $ hg status
  ? bar

  $ hg mv a foo

  $ hg ci -m "Moved a to foo"
  $ hg exp --git
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID cfef290346fbee5126313d7e1aab51d877679b09
  # Parent  03ddd6fc5af19e028c44a2fd6d790dd22712f231
  Moved a to foo
  
  diff --git a/a b/foo
  rename from a
  rename to foo

  $ hg mv b foobar
  $ hg diff --git
  diff --git a/b b/foobar
  rename from b
  rename to foobar
  $ hg amend

  $ hg exp --git
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID eca050985275bb271ce3092b54e56ea5c85d29a3
  # Parent  03ddd6fc5af19e028c44a2fd6d790dd22712f231
  Moved a to foo
  
  diff --git a/a b/foo
  rename from a
  rename to foo
  diff --git a/b b/foobar
  rename from b
  rename to foobar

  $ hg mv c wat
  $ hg unamend

Retained copies in new prdecessor commit

  $ hg exp --git
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID 552e3af4f01f620f88ca27be1f898316235b736a
  # Parent  03ddd6fc5af19e028c44a2fd6d790dd22712f231
  Moved a to foo
  
  diff --git a/a b/foo
  rename from a
  rename to foo

Retained copies in working directoy

  $ hg diff --git
  diff --git a/b b/foobar
  rename from b
  rename to foobar
  diff --git a/c b/wat
  rename from c
  rename to wat