Re: Git 2.26 fetches many times more objects than it should, wasting gigabytes

From: Jeff King <peff@peff.net>
Date: Apr 22, 2020, 10:40 UTC
Message-ID: <20200422104000.GA551233@coredump.intra.peff.net>
In-Reply-To: <20200422103011.GA545254@coredump.intra.peff.net>

On Wed, Apr 22, 2020 at 06:30:11AM -0400, Jeff King wrote:

Show 18 quoted lines

> So it really just seems like v2 does not try hard enough. I think the
> culprit is the MAX_IN_VAIN setting. If I do this:
> 
> diff --git a/fetch-pack.c b/fetch-pack.c
> index 1734a573b0..016a413d49 100644
> --- a/fetch-pack.c
> +++ b/fetch-pack.c
> @@ -46,7 +46,7 @@ static struct strbuf fsck_msg_types = STRBUF_INIT;
>   * After sending this many "have"s if we do not get any new ACK , we
>   * give up traversing our history.
>   */
> -#define MAX_IN_VAIN 256
> +#define MAX_IN_VAIN 20000
>  
>  static int multi_ack, use_sideband;
>  /* Allow specifying sha1 if it is a ref tip. */
> 
> then I get that same 48k objects, 23MB fetch that v0 does.

I don't quite think that's the solution, though. Both old and new are supposed to be respecting MAX_IN_VAIN. So it's not at all clear to me why it restricts the number of haves we'll send in v2, but not in v0.

Maybe somebody more familiar with the negotiation code can comment further.

-Peff