Re: [PATCH 0/2] Set GIT_TRACE2_EVENT_NESTING in test-lib.sh

From: Derrick Stolee <stolee@gmail.com>
Date: Nov 30, 2021, 15:34 UTC
Message-ID: <86555f24-e7c4-64cb-a55c-7e2580e895f2@gmail.com>
In-Reply-To: <YaUegEGxfAf72O9Z@coredump.intra.peff.net>

On 11/29/2021 1:40 PM, Jeff King wrote:

Show 18 quoted lines

> On Mon, Nov 29, 2021 at 01:47:44PM +0000, Derrick Stolee via GitGitGadget wrote:
> 
>> As reported by Ævar [1] and diagnosed by Peff in a reply, the default
>> GIT_TRACE2_EVENT_NESTING is set so low that tests that look for trace2
>> events can start failing due to an added trace2 region. This can even be
>> subtle, including the fact that the progress API adds trace2 regions when in
>> use (which can depend on the verbose output of a test script).
> 
> I think this is a good change for fixing the immediate problem of the
> test suite failing.
> 
> But I have to wonder if this is masking a problem that real users will
> see. Aren't we silently discarding trace2 output that could be useful to
> somebody debugging or trying to get performance metrics?
> 
> I.e., should we be bumping the internal nesting max of 2 to something
> higher? If that would that cause problems with existing metrics, should
> we be designing new metrics to avoid nesting?

One thing this makes me think about is that we might want to have items such as trace2_data_intmax() and trace2_data_string() not be subject to the nesting limit. Only have the nesting apply to the regions (which nest).

CC'ing Jeff Hostetler for his thoughts on that idea. We will have a discussion offline to see if the progress regions have started to cause inconsistencies in our existing telemetry stream of internal users.

Thanks, -Stolee