configitems: register the full 'merge-tools' config and sub-options
We register the merge-tools config section (which has an arbitrary base config
value) and the possible sub-attribute. The sub-attribute has to be registered
first or at the same time otherwise the '.*' item would shadow them.
Merge tools could include "." in their name so we can't constrain any more
than just ".*".
revlog-sparse-read: add a lower-threshold for read block size
The option experimental.sparse-read.min-block-size specifies the minimal size
of a deltachain span, under which it won't be split by _slicechunk.
revlog: introduce an experimental flag to slice chunks reads when too sparse
Delta chains can become quite sparse if there is a lot of unrelated data between
relevant pieces. Right now, revlog always reads all the necessary data for the
delta chain in one single read. This can lead to a lot of unrelated data to be
read (see
issue5482 for more details).
One can use the `experimental.maxdeltachainspan` option with a large value
(or -1) to easily produce a very sparse delta chain.
This change introduces the ability to slice the chunks retrieval into multiple
reads, skipping large sections of unrelated data. Preliminary testing shows
interesting results. For example the peak memory consumption to read a manifest
on a large repository is reduced from 600MB to 250MB (200MB without
maxdeltachainspan). However, the slicing itself and the multiple reads can have
an negative impact on performance. This is why the new feature is hidden behind
an experimental flag.
Future changesets will add various parameters to control the slicing heuristics.
We hope to experiment a wide variety of repositories during 4.4 and hopefully
turn the feature on by default in 4.5.
As a first try, the algorithm itself is prone to deep changes. However, we wish
to define APIs and have a baseline to work on.
revlog: ignore empty trailing chunks when reading segments
When a merge commit creates an empty diff in the revlog, its offset may still
be quite far from the end of the previous chunk.
Skipping these empty chunks may reduce read size significantly.
In most cases, there is no gain, and in some cases, little gain.
On my clone of pypy, `hg manifest` reads 65% less bytes (96140 i/o 275943) for
revision 4260 by ignoring the only empty trailing diff.
For revision 2229, 35% (34557 i/o 53435)
Sadly, this is difficult to reproduce, as hg clone can make its own different
structure every time.
phase: isolate logic to update remote phrase through bundle2 pushkey
Move the logic to build bundle2 pushkey part into its dedicated function. It
will help to keep the logic clear when adding support for sending phases change
using 'phase-heads' part.
phase: generate a push-race detection part on push
We are about to switch phase pushing from using pushkey to using a the new
dedicated binary part. We introduce the push race detection on its own to help
detect potential impact.