Re: [PATCH v2 00/38] Virtualization of the refs API

From: Michael Haggerty <mhagger@alum.mit.edu>
Date: Sep 8, 2016, 06:42 UTC
Message-ID: <7aac9c43-b8fc-c6fa-6311-4ff7a5495464@alum.mit.edu>
In-Reply-To: <xmqqmvjjldp2.fsf@gitster.mtv.corp.google.com>

On 09/07/2016 09:20 PM, Junio C Hamano wrote:

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> Michael Haggerty <mhagger@alum.mit.edu> writes:
> 
>> This is v2 of the patch series to virtualize the references API
>> (though earlier patch series similar in spirit were submitted by
>> Ronnie Sahlberg and David Turner). Thanks to Junio, Eric, and Ramsay
>> for their comments about v1 [1].
>>
>> Nobody pointed out any fundamental problems with v1, but this version
>> includes the following improvements:
> 
> Curiously, many of these improvements were already in 'pu'.

I pushed some of these changes to GitHub a while ago and mentioned that fact on the mailing list [1]; I assume you fetched from there. But I was waiting for the dust to settle from the earlier patch series and the 2.10 release before sending them to the mailing list again.

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>> * In "refs: add methods for reflog":
>>
>>   * Don't export `files_reflog_iterator_begin()` (suggested by
>>     Ramsay).
> 
> This I can see was missing in what has been in 'pu'.

And according to your "What's cooking", you were waiting on this change before proceeding.

FYI: I haven't done significant work on any next steps, which IMO could
go in many possible directions:

* Splitting loose and packed refs storage into two separate ref_store
subclasses that are joined together using some kind of
overlay_ref_store. This is not necessarily a blocker for the following
ideas, but the overlay_ref_store would make it easier to construct other
hybrid ref-stores, as for example the ubiquitous "most references are
stored in main repo; per-worktree refs are stored in worktree".

* Implementing reference caching as a ref_store that "writes through"
changes to a backing reference store. This is also not a blocker for
other ideas, but it would allow reference caching easily to be turned
on/off for other reference stores (or even disabled for packed/loose
reference storage during command invocations that know they won't have
to iterate over references more than once).

* A variant of loose reference storage that encodes the reference names
somehow before turning them into filenames (1) to make refnames
independent of filesystem path-name encoding issues, and (2) to
eliminate D/F conflicts, thereby allowing reflogs to be retained after a
reference is deleted.

* A reference backend based on LMDB (or any other key-value store).

* A reference backend based on Shawn Pearce's RefTree proposal or
something like it [2].

It's uncertain when I'll next have a chunk of time to work on any of these.

Michael

[1] http://public-inbox.org/git/575990FB.5000908@alum.mit.edu/ [2] http://public-inbox.org/git/CAJo=hJvnAPNAdDcAAwAvU9C4RVeQdoS3Ev9WTguHx4fD0V_nOg@mail.gmail.com/t