Gregory Szorc <gregory.szorc@gmail.com> [Thu, 02 Aug 2018 17:52:21 -0700] rev 38935
changegroup: make delta header struct formatters actual structs
Why we weren't using compiled Struct instances, I don't know. They
make code simpler. In theory they are faster. Although I don't
believe I was able to measure any meaningful change. That could be
because this code is often dominated by compression, deltafication,
and function call overhead.
Differential Revision: https://phab.mercurial-scm.org/D4078
Gregory Szorc <gregory.szorc@gmail.com> [Thu, 02 Aug 2018 17:33:23 -0700] rev 38934
changegroup: pass version into constructor
Currently, the version is an attribute on each class. Passing
the argument into the constructor gets us one step closer to
eliminating cg2packer and cg3packer.
Differential Revision: https://phab.mercurial-scm.org/D4077
Gregory Szorc <gregory.szorc@gmail.com> [Thu, 02 Aug 2018 17:29:53 -0700] rev 38933
changegroup: define functions for creating changegroup packers
Currently, we have 3 classes for changegroup generation. Each class
handles a specific changegroup format. And each subsequent version's
class inherits from the previous one.
The interface for the classes is not very well defined and a lot of
version-specific behavior is behind overloaded functions. This
approach adds complexity and makes changegroup generation difficult
to reason about.
Upcoming commits will be consolidating these 3 classes so differences
between changegroup versions and changegroup generation are controlled
by parameters to a single constructor / type rather than by
overriding class attributes via inheritance.
We begin this process by building dedicated functions for creating
each changegroup packer instance. Currently they just call the
constructor on the appropriate class. This will soon change.
Differential Revision: https://phab.mercurial-scm.org/D4076
Gregory Szorc <gregory.szorc@gmail.com> [Fri, 03 Aug 2018 10:05:26 -0700] rev 38932
changegroup: capture revision delta in a data structure
The current changegroup generation code is tightly coupled to
the revlog API. This tight coupling makes it difficult to implement
alternate storage backends without requiring a large surface area
of the revlog API to be exposed. This is not desirable.
In order to support changegroup generation with non-revlog storage,
we'll need to abstract the concept of delta generation.
This commit is the first step down that road. We introduce a
data structure for representing a delta in a changegroup.
The API still leaves a lot to be desired. But at least we now
have separation between data and actions performed on it.
As part of this, we tweak behavior slightly: we no longer
concatenate the delta prefix with the metadata header. Instead,
we track and emit the prefix as a separate chunk. This shouldn't
have any meaningful impact since all the chunks just get sent to
the wire, the compressor, etc.
Because we're introducing a new object, this does add some
overhead to changegroup execution. `hg perfchangegroupchangelog`
on my clone of the Mercurial repo (~40,000 visible revisions in
the changelog) slows down a bit:
! wall 1.268600 comb 1.270000 user 1.270000 sys 0.000000 (best of 8)
! wall 1.419479 comb 1.410000 user 1.410000 sys 0.000000 (best of 8)
With for `hg bundle -t none-v2 -a /dev/null`:
before: real 6.610 secs (user 6.460+0.000 sys 0.140+0.000)
after: real 7.210 secs (user 7.060+0.000 sys 0.140+0.000)
I plan to claw back this regression in future commits. And I may
even do away with this data structure once the refactor is complete.
For now, it makes things easier to comprehend.
Differential Revision: https://phab.mercurial-scm.org/D4075
Gregory Szorc <gregory.szorc@gmail.com> [Thu, 02 Aug 2018 16:36:40 -0700] rev 38931
changegroup: inline ellipsisdata()
There's only one caller of it. I don't think it needs to exist as
a standalone function.
Differential Revision: https://phab.mercurial-scm.org/D4074
Gregory Szorc <gregory.szorc@gmail.com> [Thu, 02 Aug 2018 17:05:11 -0700] rev 38930
changegroup: rename "revlog" variables
"revlog" shadows the module import. But more importantly, changegroup
generation should be storage agnostic and not assume the existence
of revlogs. Let's rename the thing providing revision storage to
"store" to reflect this ideal property.
Differential Revision: https://phab.mercurial-scm.org/D4073