view tests/test-narrow-shallow-merges.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

#require no-reposimplestore

  $ . "$TESTDIR/narrow-library.sh"

create full repo

  $ hg init master
  $ cd master
  $ cat >> .hg/hgrc <<EOF
  > [narrow]
  > serveellipses=True
  > EOF

  $ mkdir inside
  $ echo 1 > inside/f
  $ hg commit -Aqm 'initial inside'

  $ mkdir outside
  $ echo 1 > outside/f
  $ hg commit -Aqm 'initial outside'

  $ echo 2a > outside/f
  $ hg commit -Aqm 'outside 2a'
  $ echo 3 > inside/f
  $ hg commit -Aqm 'inside 3'
  $ echo 4a > outside/f
  $ hg commit -Aqm 'outside 4a'
  $ hg update '.~3'
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ echo 2b > outside/f
  $ hg commit -Aqm 'outside 2b'
  $ echo 3 > inside/f
  $ hg commit -Aqm 'inside 3'
  $ echo 4b > outside/f
  $ hg commit -Aqm 'outside 4b'
  $ hg update '.~3'
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ echo 2c > outside/f
  $ hg commit -Aqm 'outside 2c'
  $ echo 3 > inside/f
  $ hg commit -Aqm 'inside 3'
  $ echo 4c > outside/f
  $ hg commit -Aqm 'outside 4c'
  $ hg update '.~3'
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ echo 2d > outside/f
  $ hg commit -Aqm 'outside 2d'
  $ echo 3 > inside/f
  $ hg commit -Aqm 'inside 3'
  $ echo 4d > outside/f
  $ hg commit -Aqm 'outside 4d'

  $ hg update -r 'desc("outside 4a")'
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg merge -r 'desc("outside 4b")' 2>&1 | egrep -v '(warning:|incomplete!)'
  merging outside/f
  0 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
  $ echo 5 > outside/f
  $ rm outside/f.orig
  $ hg resolve --mark outside/f
  (no more unresolved files)
  $ hg commit -m 'merge a/b 5'
  $ echo 6 > outside/f
  $ hg commit -Aqm 'outside 6'

  $ hg merge -r 'desc("outside 4c")' 2>&1 | egrep -v '(warning:|incomplete!)'
  merging outside/f
  0 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
  $ echo 7 > outside/f
  $ rm outside/f.orig
  $ hg resolve --mark outside/f
  (no more unresolved files)
  $ hg commit -Aqm 'merge a/b/c 7'
  $ echo 8 > outside/f
  $ hg commit -Aqm 'outside 8'

  $ hg merge -r 'desc("outside 4d")' 2>&1 | egrep -v '(warning:|incomplete!)'
  merging outside/f
  0 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
  $ echo 9 > outside/f
  $ rm outside/f.orig
  $ hg resolve --mark outside/f
  (no more unresolved files)
  $ hg commit -Aqm 'merge a/b/c/d 9'
  $ echo 10 > outside/f
  $ hg commit -Aqm 'outside 10'

  $ echo 11 > inside/f
  $ hg commit -Aqm 'inside 11'
  $ echo 12 > outside/f
  $ hg commit -Aqm 'outside 12'

  $ hg log -G -T '{rev} {node|short} {desc}\n'
  @  21 8d874d57adea outside 12
  |
  o  20 7ef88b4dd4fa inside 11
  |
  o  19 2a20009de83e outside 10
  |
  o    18 3ac1f5779de3 merge a/b/c/d 9
  |\
  | o  17 38a9c2f7e546 outside 8
  | |
  | o    16 094aa62fc898 merge a/b/c 7
  | |\
  | | o  15 f29d083d32e4 outside 6
  | | |
  | | o    14 2dc11382541d merge a/b 5
  | | |\
  o | | |  13 27d07ef97221 outside 4d
  | | | |
  o | | |  12 465567bdfb2d inside 3
  | | | |
  o | | |  11 d1c61993ec83 outside 2d
  | | | |
  | o | |  10 56859a8e33b9 outside 4c
  | | | |
  | o | |  9 bb96a08b062a inside 3
  | | | |
  | o | |  8 b844052e7b3b outside 2c
  |/ / /
  | | o  7 9db2d8fcc2a6 outside 4b
  | | |
  | | o  6 6418167787a6 inside 3
  | | |
  +---o  5 77344f344d83 outside 2b
  | |
  | o  4 9cadde08dc9f outside 4a
  | |
  | o  3 019ef06f125b inside 3
  | |
  | o  2 75e40c075a19 outside 2a
  |/
  o  1 906d6c682641 initial outside
  |
  o  0 9f8e82b51004 initial inside
  

Now narrow and shallow clone this and get a hopefully correct graph

  $ cd ..
  $ hg clone --narrow ssh://user@dummy/master narrow --include inside --depth 7
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 8 changesets with 3 changes to 1 files
  new changesets *:* (glob)
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd narrow

To make updating the tests easier, we print the emitted nodes
sorted. This makes it easier to identify when the same node structure
has been emitted, just in a different order.

  $ hg log -G -T '{rev} {node|short}{if(ellipsis,"...")} {desc}\n'
  @  7 8d874d57adea... outside 12
  |
  o  6 7ef88b4dd4fa inside 11
  |
  o  5 2a20009de83e... outside 10
  |
  o    4 3ac1f5779de3... merge a/b/c/d 9
  |\
  | o  3 465567bdfb2d inside 3
  | |
  | o  2 d1c61993ec83... outside 2d
  |
  o  1 bb96a08b062a inside 3
  |
  o  0 b844052e7b3b... outside 2c
  

  $ hg log -T '{if(ellipsis,"...")}{node|short} {p1node|short} {p2node|short} {desc}\n' | sort
  ...2a20009de83e 000000000000 3ac1f5779de3 outside 10
  ...3ac1f5779de3 bb96a08b062a 465567bdfb2d merge a/b/c/d 9
  ...8d874d57adea 7ef88b4dd4fa 000000000000 outside 12
  ...b844052e7b3b 000000000000 000000000000 outside 2c
  ...d1c61993ec83 000000000000 000000000000 outside 2d
  465567bdfb2d d1c61993ec83 000000000000 inside 3
  7ef88b4dd4fa 2a20009de83e 000000000000 inside 11
  bb96a08b062a b844052e7b3b 000000000000 inside 3

  $ cd ..

Incremental test case: show a pull can pull in a conflicted merge even if elided

  $ hg init pullmaster
  $ cd pullmaster
  $ cat >> .hg/hgrc <<EOF
  > [narrow]
  > serveellipses=True
  > EOF
  $ mkdir inside outside
  $ echo v1 > inside/f
  $ echo v1 > outside/f
  $ hg add inside/f outside/f
  $ hg commit -m init

  $ for line in a b c d
  > do
  > hg update -r 0
  > echo v2$line > outside/f
  > hg commit -m "outside 2$line"
  > echo v2$line > inside/f
  > hg commit -m "inside 2$line"
  > echo v3$line > outside/f
  > hg commit -m "outside 3$line"
  > echo v4$line > outside/f
  > hg commit -m "outside 4$line"
  > done
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  created new head
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  created new head
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  created new head

  $ cd ..
  $ hg clone --narrow ssh://user@dummy/pullmaster pullshallow \
  >          --include inside --depth 3
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 12 changesets with 5 changes to 1 files (+3 heads)
  new changesets *:* (glob)
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd pullshallow

  $ hg log -G -T '{rev} {node|short}{if(ellipsis,"...")} {desc}\n'
  @  11 0ebbd712a0c8... outside 4d
  |
  o  10 0d4c867aeb23 inside 2d
  |
  o  9 e932969c3961... outside 2d
  
  o  8 33d530345455... outside 4c
  |
  o  7 0ce6481bfe07 inside 2c
  |
  o  6 caa65c940632... outside 2c
  
  o  5 3df233defecc... outside 4b
  |
  o  4 7162cc6d11a4 inside 2b
  |
  o  3 f2a632f0082d... outside 2b
  
  o  2 b8a3da16ba49... outside 4a
  |
  o  1 53f543eb8e45 inside 2a
  |
  o  0 1be3e5221c6a... outside 2a
  
  $ hg log -T '{if(ellipsis,"...")}{node|short} {p1node|short} {p2node|short} {desc}\n' | sort
  ...0ebbd712a0c8 0d4c867aeb23 000000000000 outside 4d
  ...1be3e5221c6a 000000000000 000000000000 outside 2a
  ...33d530345455 0ce6481bfe07 000000000000 outside 4c
  ...3df233defecc 7162cc6d11a4 000000000000 outside 4b
  ...b8a3da16ba49 53f543eb8e45 000000000000 outside 4a
  ...caa65c940632 000000000000 000000000000 outside 2c
  ...e932969c3961 000000000000 000000000000 outside 2d
  ...f2a632f0082d 000000000000 000000000000 outside 2b
  0ce6481bfe07 caa65c940632 000000000000 inside 2c
  0d4c867aeb23 e932969c3961 000000000000 inside 2d
  53f543eb8e45 1be3e5221c6a 000000000000 inside 2a
  7162cc6d11a4 f2a632f0082d 000000000000 inside 2b

  $ cd ../pullmaster
  $ hg update -r 'desc("outside 4a")'
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg merge -r 'desc("outside 4b")' 2>&1 | egrep -v '(warning:|incomplete!)'
  merging inside/f
  merging outside/f
  0 files updated, 0 files merged, 0 files removed, 2 files unresolved
  use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon
  $ echo 3 > inside/f
  $ echo 5 > outside/f
  $ rm -f {in,out}side/f.orig
  $ hg resolve --mark inside/f outside/f
  (no more unresolved files)
  $ hg commit -m 'merge a/b 5'

  $ hg update -r 'desc("outside 4c")'
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg merge -r 'desc("outside 4d")' 2>&1 | egrep -v '(warning:|incomplete!)'
  merging inside/f
  merging outside/f
  0 files updated, 0 files merged, 0 files removed, 2 files unresolved
  use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon
  $ echo 3 > inside/f
  $ echo 5 > outside/f
  $ rm -f {in,out}side/f.orig
  $ hg resolve --mark inside/f outside/f
  (no more unresolved files)
  $ hg commit -m 'merge c/d 5'

  $ hg update -r 'desc("merge a/b 5")'
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg merge -r 'desc("merge c/d 5")'
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ echo 6 > outside/f
  $ hg commit -m 'outside 6'
  $ echo 7 > outside/f
  $ hg commit -m 'outside 7'
  $ echo 8 > outside/f
  $ hg commit -m 'outside 8'

  $ cd ../pullshallow
  $ hg pull --depth 3
  pulling from ssh://user@dummy/pullmaster
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 4 changesets with 3 changes to 1 files (-3 heads)
  new changesets *:* (glob)
  (run 'hg update' to get a working copy)

  $ hg log -T '{if(ellipsis,"...")}{node|short} {p1node|short} {p2node|short} {desc}\n' | sort
  ...0ebbd712a0c8 0d4c867aeb23 000000000000 outside 4d
  ...1be3e5221c6a 000000000000 000000000000 outside 2a
  ...33d530345455 0ce6481bfe07 000000000000 outside 4c
  ...3df233defecc 7162cc6d11a4 000000000000 outside 4b
  ...b8a3da16ba49 53f543eb8e45 000000000000 outside 4a
  ...bf545653453e 968003d40c60 000000000000 outside 8
  ...caa65c940632 000000000000 000000000000 outside 2c
  ...e932969c3961 000000000000 000000000000 outside 2d
  ...f2a632f0082d 000000000000 000000000000 outside 2b
  0ce6481bfe07 caa65c940632 000000000000 inside 2c
  0d4c867aeb23 e932969c3961 000000000000 inside 2d
  53f543eb8e45 1be3e5221c6a 000000000000 inside 2a
  67d49c0bdbda b8a3da16ba49 3df233defecc merge a/b 5
  7162cc6d11a4 f2a632f0082d 000000000000 inside 2b
  968003d40c60 67d49c0bdbda e867021d52c2 outside 6
  e867021d52c2 33d530345455 0ebbd712a0c8 merge c/d 5