Re: [RFC/PATCH 0/8] Add configuration options for split-index

On Sat, Jul 23, 2016 at 6:11 PM, Christian Couder
[off-list ref] wrote:

Ok, I started working on automatically pushing back all changes to the
shared index when the percentage of entries in linked vs shared
indexes is greater than 25% (maybe I will make it configurable later).
It is very basic and doesn't work well for now (for one thing it is
missing added entries), see:

https://github.com/chriscool/git/commits/config-split-index8

Basically I would like a way to count then entries that are only in
the linked index without modifying them to be safe, but I have a hard
time seeing how I could modify prepare_to_write_split_index() to get
that.

Hmm.. can you do the counting separately? A shared cache_entry must
have its field "index" greater than zero. By counting the number of
entries whose index is zero (i.e. not shared) against the total number
of real (*) entries, you should have a decent estimate when to split.
Then you can do exactly what "git update-index --no-split-index" and
"git update-index --split-index" sequence does, but in write_index().
It's easier than messing inside split-index.c. If we hit performance
problem, then we can look into changing split-index.c

(*) remember that some entries may be marked CE_REMOVE, which are dead
entries and should not be counted because they will never be written
down on disk.
-- 
Duy