Re: [PATCH 3/3] revision: insert unsorted, then sort in prepare_revision_walk()

> On Mon, Apr 2, 2012 at 09:49, Martin Fick <mfick@codeaurora.org> wrote:
>> On Monday, April 02, 2012 10:39:59 am Shawn Pearce wrote:
>>> On Mon, Apr 2, 2012 at 09:24, Martin Fick
>> <mfick@codeaurora.org> wrote:
>>> > On Saturday, March 31, 2012 04:11:01 pm René Scharfe
>> wrote:
>>> Git can't really do the same thing as "cache the
>>> RevWalk". Its spawning a new process that needs to
>>> decompress and parse each commit object to determine its
>>> timestamp so the commits can be sorted into the priority
>>> queue. This is still an O(N) operation given N
>>> references.
>>
>> While I suspect this has been suggested before, an ondisk
>> cache of commits to timestamps would probably help here with
>> large repos.  Such a cache could make even new processes
>> able to create this list much quicker.  Since this cache
>> would contain immutable data, even if it is out of date it
>> would likely provided significant improvements by providing
>> most of the timestamps leaving only a few to parse from
>> newer commits?
>
> Probably. But we tend to hate caches in Git because they can get stale
> and need to be rebuilt, and are redundant with the base data. The
> mythical "pack v4" work was going to approach this problem by storing
> the commit timestamps uncompressed in a more machine friendly format.
> Unfortunately the work has been stalled for years.

>> By the way, is latest packv4 code available somewhere to fetch?
>
> Well, not yet.  Incidentally, I'm going in the Caribbeans for a week in
> a week, with no kids and only my wife who is going to be busy with scuba
> diving activities.  Like I did last year, I'm going to take some time to
> pursue my work on Pack v4 during that time.  And I intend to publish it
> when I come back, whatever state it is in, so someone else can complete
> the work eventually (I have too much to do to spend significant time on
> Git these days).