comparison mercurial/help/internals/revlogs.txt @ 41202:e7a2cc84dbc0

revlog: always enable generaldelta on version 2 revlogs

This commit starts the process of diverging version 2 revlogs
from version 1 revlogs.

generaldelta is a useful feature and has been enabled by
default for ages. I can't think of a good reason why the
feature should be disabled. Yes, it is true changelogs
today don't have generaldelta enabled. But that's because
they don't have delta chains enabled, so generaldelta makes
no sense there.

This commit makes generaldelta always enabled on version 2
revlogs.

As part of this, one-off code in changelog.py mucking with
revlog.version had to be made conditional on the revlog
version, as we don't want to change revlog feature
flags on version 2 revlogs. The fact this code exists
is horrible and stems from revlog options being shared by
the opener. We probably want a better API here. But that can
wait for another patch.

Differential Revision: https://phab.mercurial-scm.org/D5561

41201:6439cefaeb64

Version 2 revlogs have the following flags at the specified bit offsets:

0
   Store revision data inline.
1
   Generaldelta encoding.

The following header values are common:

00 00 00 01
   v1

Version 2 Format
================

(In development. Format not finalized or stable.)

Version 2 is currently identical to version 1. This will obviously
change.

Delta Chains
============

Revision data is encoded as a chain of *chunks*. Each chain begins with

41202:e7a2cc84dbc0

Version 2 revlogs have the following flags at the specified bit offsets:

0
   Store revision data inline.

The following header values are common:

00 00 00 01
   v1

Version 2 Format
================

(In development. Format not finalized or stable.)

Version 2 is identical to version 2 with the following differences.

There is no dedicated *generaldelta* revlog format flag. Instead,
the feature is implied enabled by default.

Delta Chains
============

Revision data is encoded as a chain of *chunks*. Each chain begins with