[PATCH 1 of 6 RFC] localrepo: establish a base class for an immutable local repository

[Pierre-Yves David]

On 06/09/2017 07:31 PM, Gregory Szorc wrote:
> On Fri, Jun 9, 2017 at 2:59 AM, Pierre-Yves David <
> pierre-yves.david at ens-lyon.org> wrote:
>
>>
>>
>> On 06/09/2017 07:36 AM, Gregory Szorc wrote:
>>
>>> # HG changeset patch
>>> # User Gregory Szorc <gregory.szorc at gmail.com>
>>> # Date 1496977416 25200
>>> #      Thu Jun 08 20:03:36 2017 -0700
>>> # Node ID dfe0db942bbf860968b19fd8579865790d78d5e8
>>> # Parent  e583b786ffba99cb775cf9d3a126cf50db74f85a
>>> localrepo: establish a base class for an immutable local repository
>>>
>>
>> I like the general idea and direction of this series. Moving toward more
>> guarantee of having a consistent view of the repository is great.
>>
>
> Obviously the current repo store design can't be fully consistent because
> there are race conditions between process A opening files and process B
> mutating them. However, my utopia end state is we devise a storage model
> (either based completely on append-only data structures or on
> file/directory based "generations" for data that isn't append-only) and
> readers can read a single file denoting current offsets/generations to get
> an atomic and consistent view of a repo.

We are on the same page here.
I'm not sure how much code you have written about the above yet. I've a 
series that will allow to introduce more vfs to distinct the various 
types of files we have (wc related, append only, etc). I made good 
progress on it last September but it needed some rework and I did not 
had time to back to it yet. There are founding for it so this should 
happen soonish.

Cheers,

-- 
Pierre-Yves David