feat(sampling-in-storage): preflight mode

[xurui-c]

Implements preflight mode according to https://github.com/getsentry/eap-planning/issues/212

https://github.com/getsentry/eap-planning/issues/217

NOTE: DEPENDS ON #6981

[codecov]

❌ 1 Tests Failed:

Tests completed	Failed	Passed	Skipped
219	1	218	0

View the top 1 failed test(s) by shortest run time

tests.test_generic_metrics_api.TestGenericMetricsApiDistributions::test_retrieval_basic_sampled

Stack Traces | 0.413s run time

Traceback (most recent call last):
  File ".../snuba/tests/test_generic_metrics_api.py", line 354, in test_retrieval_basic_sampled
    assert data["data"][0]["dist_sum"] == 400.0
AssertionError: assert 200.0 == 400.0

To view more test analytics, go to the Test Analytics Dashboard
_{📋 Got 3 mins? Take this short survey to help us improve Test Analytics.}

[onkar]

I know this is a draft PR, but left a few comments.

[volokluev]

Looks good overall, let's just remove the seeded RNGs and just test that:

1. the preflight mode returns fewer queries
2. the response metadata is updated correctly

[onkar]

LGTM mostly, added a few nits. Didn't look into the test failures, but are those happening because of the use of random? Maybe better to simplify to not use random if that is the cause of the failure.

[onkar]

nit: naming could be changed to something more specific like set_sampling_tier_512 to be explicit. Also, I see that this function is called conditionally, so that condition can be handled inside this function instead of outside:

def set_sampling_tier_512(
    request: TimeSeriesRequest | TraceItemTableRequest,
    query_settings: HTTPQuerySettings,
) -> None:
    if not request.meta.HasField("downsampled_storage_config"):
        return  # No downsampled storage config, so do nothing

    if (
        request.meta.downsampled_storage_config.mode
        == DownsampledStorageConfig.MODE_PREFLIGHT
    ):
        query_settings.set_sampling_tier(Tier.TIER_512)

[xurui-c]

If the mode isn't preflight we shouldn't add tier 512 to query settings. the behavior of the function depends on the mode so I didn't want to specify which tier we're setting in the name

[onkar]

This and other occurrences become:

set_sampling_tier_512(request, query_settings)

[volokluev]

mostly good., just a few comments

[davidtsuk]

lgtm