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From: Jonathan Tan <jonathantanmy@google.com>
To: peff@peff.net
Cc: jonathantanmy@google.com, gitster@pobox.com, git@vger.kernel.org
Subject: Re: [RFC PATCH] Modify fetch-pack to no longer die on error?
Date: Wed, 29 Jul 2020 11:53:47 -0700	[thread overview]
Message-ID: <20200729185347.653706-1-jonathantanmy@google.com> (raw)
In-Reply-To: <20200728200847.GA1019822@coredump.intra.peff.net>

> On Tue, Jul 28, 2020 at 12:23:50PM -0700, Jonathan Tan wrote:
> 
> > > For this particular case, with the performance and all, I agree that
> > > the stupid and robust approach would be the best.
> > 
> > I'm concerned that we will be painting ourselves into a corner here - I
> > have been appreciating the richer interface that a C call provides us,
> > compared to sub-processes where we have to communicate through a single
> > input stream and a single output stream. For example, "wanted-refs" and
> > [...]
> 
> Yeah, that's a compelling reason. I'd have thought for this use case you
> could just say "hey, make sure these objects exist", which doesn't
> require a lot of communication. But often when I think things like that
> and start coding, it turns out to be much more complicated. So I am
> perfectly willing to believe you that it doesn't apply here. And even
> if it did, you're right that we may run into other spots that do need to
> pass back more information, but benefit from more lib-ified code that
> doesn't die().

Thanks. Just to be clear, I can't think of any hard stops to
implementing lazy fetch in a sub-process right now, but (as you said)
while programming I could discover something, or we could need something
in the future.

> Just to play devil's advocate for a moment...
> 
> > (Also, I think that debugging within a process is easier than debugging
> > across processes, but that might not be a concern that other people
> > share.)
> 
> This is definitely true sometimes, but I think is sometimes the
> opposite. When we push things out to a sub-process, then the interface
> between the two processes has to be well-defined (e.g., writing results
> to a file with a particular format). And that can make debugging easier,
> because you can pick up from that intermediate state (munging it in the
> middle, or even generating it from scratch for testing).

Well, unless there is some sort of interactivity like in remote helpers
:-)

> Likewise, that can result in a more flexible and robust system from the
> perspective of users. If we had invented "git log" first, we probably
> wouldn't have "git rev-list | git diff-tree --stdin" at all. But having
> that as two separate tools is sometimes useful for people doing things
> _besides_ log, since it gives different entry points to the code.

That's true. And the lazy fetch might be one of them - after looking at
the code, I think that I can get to where I want just by implementing a
null negotiator, which will be useful for end users. (In particular,
simulating a lazy fetch might be useful sometimes, and re-fetching a
packfile could be a crude way of repairing object corruption.)

> That said, I think I could buy the argument that "fetch" works pretty
> well as a basic building block for users. It's pretty rare to actually
> use fetch-pack as a distinct operation. This is all a monolith vs module
> tradeoff question, and the tradeoff around modularity for fetch isn't
> that compelling.

If we are going the sub-process route, I was planning to use "fetch" as
the sub-process, actually, not "fetch-pack" - among other things,
"fetch" allows us to specify a fetch negotiator. So it seems like you
are saying that if we had to use "fetch-pack", you have no problem with
libifying it and calling it in the same process, but if we can use
"fetch", we should use it as a sub-process?

In any case, I'll look into using "fetch" as a sub-process and see if it
works.

  reply	other threads:[~2020-07-29 18:53 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-24 22:38 Jonathan Tan
2020-07-24 23:07 ` Junio C Hamano
2020-07-24 23:11 ` Junio C Hamano
2020-07-25 21:41   ` Jeff King
2020-07-25 23:01     ` Junio C Hamano
2020-07-27 17:11       ` Jeff King
2020-07-28 19:23       ` Jonathan Tan
2020-07-28 20:08         ` Jeff King
2020-07-29 18:53           ` Jonathan Tan [this message]
2020-07-29 19:29             ` Jeff King
2020-07-29 19:02           ` Junio C Hamano
2020-07-29 22:55             ` Jonathan Tan
2020-08-05  1:20 ` [RFC PATCH 0/7] Lazy fetch with subprocess Jonathan Tan
2020-08-05  1:20   ` [RFC PATCH 1/7] fetch-pack: allow NULL negotiator->add_tip Jonathan Tan
2020-08-05 19:53     ` Junio C Hamano
2020-08-07 20:53       ` Jonathan Tan
2020-08-05  1:20   ` [RFC PATCH 2/7] fetch-pack: allow NULL negotiator->known_common Jonathan Tan
2020-08-05 20:08     ` Junio C Hamano
2020-08-05 22:11       ` Junio C Hamano
2020-08-07 20:59         ` Jonathan Tan
2020-08-05  1:20   ` [RFC PATCH 3/7] negotiator/null: add null fetch negotiator Jonathan Tan
2020-08-05  1:20   ` [RFC PATCH 4/7] fetch: --stdin Jonathan Tan
2020-08-05 20:33     ` Junio C Hamano
2020-08-07 21:10       ` Jonathan Tan
2020-08-07 21:58         ` Junio C Hamano
2020-08-07 21:10       ` Jonathan Tan
2020-08-05  1:20   ` [RFC PATCH 5/7] fetch: submodule config Jonathan Tan
2020-08-05  1:20   ` [RFC PATCH 6/7] fetch: only populate existing_refs if needed Jonathan Tan
2020-08-05  1:20   ` [RFC PATCH 7/7] promisor-remote: use subprocess to fetch Jonathan Tan
2020-08-11 22:52 ` [PATCH v2 0/7] Lazy fetch with subprocess Jonathan Tan
2020-08-11 22:52   ` [PATCH v2 1/7] negotiator/null: add null fetch negotiator Jonathan Tan
2020-08-12 12:55     ` Derrick Stolee
2020-08-12 16:44       ` Junio C Hamano
2020-08-12 17:29         ` Jonathan Tan
2020-08-11 22:52   ` [PATCH v2 2/7] fetch: allow refspecs specified through stdin Jonathan Tan
2020-08-11 22:52   ` [PATCH v2 3/7] fetch: avoid reading submodule config until needed Jonathan Tan
2020-08-12 17:34     ` Junio C Hamano
2020-08-11 22:52   ` [PATCH v2 4/7] fetch: only populate existing_refs if needed Jonathan Tan
2020-08-12 18:06     ` Junio C Hamano
2020-08-11 22:52   ` [PATCH v2 5/7] fetch-pack: do not lazy-fetch during ref iteration Jonathan Tan
2020-08-12 18:25     ` Junio C Hamano
2020-08-11 22:52   ` [PATCH v2 6/7] promisor-remote: lazy-fetch objects in subprocess Jonathan Tan
2020-08-12 18:28     ` Junio C Hamano
2020-08-11 22:52   ` [PATCH v2 7/7] fetch-pack: remove no_dependents code Jonathan Tan
2020-08-12 12:51   ` [PATCH v2 0/7] Lazy fetch with subprocess Derrick Stolee
2020-08-18  4:01 ` [PATCH v3 " Jonathan Tan
2020-08-18  4:01   ` [PATCH v3 1/7] negotiator/noop: add noop fetch negotiator Jonathan Tan
2020-08-18  4:01   ` [PATCH v3 2/7] fetch: allow refspecs specified through stdin Jonathan Tan
2020-08-18  4:01   ` [PATCH v3 3/7] fetch: avoid reading submodule config until needed Jonathan Tan
2020-08-18  4:01   ` [PATCH v3 4/7] fetch: only populate existing_refs if needed Jonathan Tan
2020-08-18  4:01   ` [PATCH v3 5/7] fetch-pack: do not lazy-fetch during ref iteration Jonathan Tan
2020-08-18  4:01   ` [PATCH v3 6/7] promisor-remote: lazy-fetch objects in subprocess Jonathan Tan
2020-08-18  4:01   ` [PATCH v3 7/7] fetch-pack: remove no_dependents code Jonathan Tan
2020-08-18 19:56   ` [PATCH v3 0/7] Lazy fetch with subprocess Junio C Hamano
2020-08-18 22:32     ` Junio C Hamano
2020-08-18 23:36       ` [PATCH] fixup! promisor-remote: lazy-fetch objects in subprocess Jonathan Tan
2020-08-18 23:57         ` Junio C Hamano

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