Subject: Re: [PATCH 0/3] reftable: graceful concurrent writes

From: Patrick Steinhardt <[email-masked]>
Date: Wed, 18 Sep 2024 06:31:25 +0200

On Tue, Sep 17, 2024 at 11:26:58AM -0700, karthik nayak wrote:
> Patrick Steinhardt <[email-masked]> writes:
> 
> > Hi,
> >
> > the reftable backend cannot properly handle concurrent writes due to two
> > reasons:
> >
> >   - It will bail out immediately when it sees a locked "tables.list"
> >     file. This is being addressed by introducing a configurable locking
> >     timeout, similar to how we have it for both loose and packed refs.
> >
> >   - It will bail out when it notices that its stack is out-of-date after
> >     having locked the "tables.list" file. This is addressed by reloading
> >     the stack as requested after locking it, which is fine because our
> >     transactional API would verify queued ref updates against their
> >     expected state after the lock was acquired anyway.
> >
> > So with this patch series we can now spawn concurrent writers and they
> > are expected to succeed, which is demonstrated by the test added by the
> > last patch.
> >
> 
> I only had a comment in the first commit. The rest two look good to me.
> I do wonder if we really need a flag? But that's just a nit.

I didn't carefully vet all locations where we could pass that flag, so
right now we only pass it in a single location. Also, we need to keep in
mind that this is library code: even if we had converted all callsites
to pass the new flag I still it's a sensibe thing to wish for to disable
the automatic refresh and abort instead.

Thanks for your review!

Patrick