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view tests/test-issue522.t @ 32697:19b9fc40cc51
revlog: skeleton support for version 2 revlogs
There are a number of improvements we want to make to revlogs
that will require a new version - version 2. It is unclear what the
full set of improvements will be or when we'll be done with them.
What I do know is that the process will likely take longer than a
single release, will require input from various stakeholders to
evaluate changes, and will have many contentious debates and
bikeshedding.
It is unrealistic to develop revlog version 2 up front: there
are just too many uncertainties that we won't know until things
are implemented and experiments are run. Some changes will also
be invasive and prone to bit rot, so sitting on dozens of patches
is not practical.
This commit introduces skeleton support for version 2 revlogs in
a way that is flexible and not bound by backwards compatibility
concerns.
An experimental repo requirement for denoting revlog v2 has been
added. The requirement string has a sub-version component to it.
This will allow us to declare multiple requirements in the course
of developing revlog v2. Whenever we change the in-development
revlog v2 format, we can tweak the string, creating a new
requirement and locking out old clients. This will allow us to
make as many backwards incompatible changes and experiments to
revlog v2 as we want. In other words, we can land code and make
meaningful progress towards revlog v2 while still maintaining
extreme format flexibility up until the point we freeze the
format and remove the experimental labels.
To enable the new repo requirement, you must supply an experimental
and undocumented config option. But not just any boolean flag
will do: you need to explicitly use a value that no sane person
should ever type. This is an additional guard against enabling
revlog v2 on an installation it shouldn't be enabled on. The
specific scenario I'm trying to prevent is say a user with a
4.4 client with a frozen format enabling the option but then
downgrading to 4.3 and accidentally creating repos with an
outdated and unsupported repo format. Requiring a "challenge"
string should prevent this.
Because the format is not yet finalized and I don't want to take
any chances, revlog v2's version is currently 0xDEAD. I figure
squatting on a value we're likely never to use as an actual revlog
version to mean "internal testing only" is acceptable. And
"dead" is easily recognized as something meaningful.
There is a bunch of cleanup that is needed before work on revlog
v2 begins in earnest. I plan on doing that work once this patch
is accepted and we're comfortable with the idea of starting down
this path.
author | Gregory Szorc <gregory.szorc@gmail.com> |
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date | Fri, 19 May 2017 20:29:11 -0700 |
parents | 2fc86d92c4a9 |
children | 009d0283de5f |
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https://bz.mercurial-scm.org/522 In the merge below, the file "foo" has the same contents in both parents, but if we look at the file-level history, we'll notice that the version in p1 is an ancestor of the version in p2. This test makes sure that we'll use the version from p2 in the manifest of the merge revision. $ hg init $ echo foo > foo $ hg ci -qAm 'add foo' $ echo bar >> foo $ hg ci -m 'change foo' $ hg backout -r tip -m 'backout changed foo' reverting foo changeset 2:4d9e78aaceee backs out changeset 1:b515023e500e $ hg up -C 0 1 files updated, 0 files merged, 0 files removed, 0 files unresolved $ touch bar $ hg ci -qAm 'add bar' $ hg merge --debug searching for copies back to rev 1 unmatched files in local: bar resolving manifests branchmerge: True, force: False, partial: False ancestor: bbd179dfa0a7, local: 71766447bdbb+, remote: 4d9e78aaceee foo: remote is newer -> g getting foo 1 files updated, 0 files merged, 0 files removed, 0 files unresolved (branch merge, don't forget to commit) $ hg debugstate | grep foo m 0 -2 unset foo $ hg st -A foo M foo $ hg ci -m 'merge' $ hg manifest --debug | grep foo c6fc755d7e68f49f880599da29f15add41f42f5a 644 foo $ hg debugindex foo rev offset length ..... linkrev nodeid p1 p2 (re) 0 0 5 ..... 0 2ed2a3912a0b 000000000000 000000000000 (re) 1 5 9 ..... 1 6f4310b00b9a 2ed2a3912a0b 000000000000 (re) 2 14 5 ..... 2 c6fc755d7e68 6f4310b00b9a 000000000000 (re)