Querier Panic - index out of range [2] with length 2

[Setheck]

Thanos, Prometheus and Golang version used:
thanos container 0.37.2 deployed from helm 15.9.2

Object Storage Provider:
s3

What happened:
Query service seemed to panic out of nowhere

What you expected to happen:
Not to panic.

How to reproduce it (as minimally and precisely as possible):
unsure, this seems like a simple range check error

Full logs to relevant components:

Logs

2025/02/24 18:52:57 http: panic serving 127.0.0.1:51276: runtime error: index out of range [2] with length 2
goroutine 727734 [running]:
net/http.(*conn).serve.func1()
	/opt/bitnami/go/src/net/http/server.go:1947 +0xbe
panic({0x29d7060?, 0xc001df18d8?})
	/opt/bitnami/go/src/runtime/panic.go:785 +0x132
github.com/thanos-io/thanos/internal/cortex/querier/queryrange.AnalyzesMerge({0xc0018fef90, 0x2, 0x2})
	/bitnami/blacksmith-sandox/thanos-0.37.2/src/github.com/thanos-io/thanos/internal/cortex/querier/queryrange/query_range.go:239 +0x12a
github.com/thanos-io/thanos/internal/cortex/querier/queryrange.prometheusCodec.MergeResponse({}, {0x4788bf?, 0x20?}, {0xc001ebf200, 0x2, 0x2})
	/bitnami/blacksmith-sandox/thanos-0.37.2/src/github.com/thanos-io/thanos/internal/cortex/querier/queryrange/query_range.go:282 +0x5ce
github.com/thanos-io/thanos/pkg/queryfrontend.downsampled.Do({{0x39b8700, 0xc00096b6c0}, {0x39b87e0, 0xc0001a0b10}, {0x39e3438, 0xc0010e46c0}}, {0x39d9f18, 0xc001e7a4e0}, {0x39f7be0, 0xc001dd3a00})
	/bitnami/blacksmith-sandox/thanos-0.37.2/src/github.com/thanos-io/thanos/pkg/queryfrontend/downsampled.go:89 +0x32a
github.com/thanos-io/thanos/pkg/queryfrontend.newQueryRangeTripperware.InstrumentMiddleware.func5.1.1({0x39d9f18?, 0xc001e7a4e0?})
	/bitnami/blacksmith-sandox/thanos-0.37.2/src/github.com/thanos-io/thanos/internal/cortex/querier/queryrange/instrumentation.go:31 +0x43
github.com/weaveworks/common/instrument.CollectedRequest({0x39d9f18, 0xc001e7a4b0}, {0x2ba80b0, 0xb}, {0x39d0a08, 0xc000966970}, 0xc000100008?, 0xc0009ca3d0)
	/bitnami/blacksmith-sandox/thanos-0.37.2/pkg/mod/github.com/weaveworks/[email protected]/instrument/instrument.go:167 +0x25d
github.com/thanos-io/thanos/pkg/queryfrontend.newQueryRangeTripperware.InstrumentMiddleware.func5.1({0x39d9f18?, 0xc001e7a4b0?}, {0x39f7be0?, 0xc001dd3a00?})
	/bitnami/blacksmith-sandox/thanos-0.37.2/src/github.com/thanos-io/thanos/internal/cortex/querier/queryrange/instrumentation.go:29 +0x96
github.com/thanos-io/thanos/internal/cortex/querier/queryrange.HandlerFunc.Do(0xc001dd3900?, {0x39d9f18?, 0xc001e7a4b0?}, {0x39f7be0?, 0xc001dd3a00?})
	/bitnami/blacksmith-sandox/thanos-0.37.2/src/github.com/thanos-io/thanos/internal/cortex/querier/queryrange/roundtrip.go:86 +0x37
github.com/thanos-io/thanos/internal/cortex/querier/queryrange.stepAlign.Do({{0x39b8700?, 0xc00096b7c0?}}, {0x39d9f18, 0xc001e7a4b0}, {0x39f7be0, 0xc001dd3900})
	/bitnami/blacksmith-sandox/thanos-0.37.2/src/github.com/thanos-io/thanos/internal/cortex/querier/queryrange/step_align.go:25 +0x178
github.com/thanos-io/thanos/pkg/queryfrontend.newQueryRangeTripperware.InstrumentMiddleware.func4.1.1({0x39d9f18?, 0xc001e7a4b0?})
	/bitnami/blacksmith-sandox/thanos-0.37.2/src/github.com/thanos-io/thanos/internal/cortex/querier/queryrange/instrumentation.go:31 +0x43
github.com/weaveworks/common/instrument.CollectedRequest({0x39d9f18, 0xc001e7a480}, {0x2ba5d73, 0xa}, {0x39d0a08, 0xc000966968}, 0x0?, 0xc0009ca670)
	/bitnami/blacksmith-sandox/thanos-0.37.2/pkg/mod/github.com/weaveworks/[email protected]/instrument/instrument.go:167 +0x25d
github.com/thanos-io/thanos/pkg/queryfrontend.newQueryRangeTripperware.InstrumentMiddleware.func4.1({0x39d9f18?, 0xc001e7a480?}, {0x39f7be0?, 0xc001dd3900?})
	/bitnami/blacksmith-sandox/thanos-0.37.2/src/github.com/thanos-io/thanos/internal/cortex/querier/queryrange/instrumentation.go:29 +0x96
github.com/thanos-io/thanos/internal/cortex/querier/queryrange.HandlerFunc.Do(0x10?, {0x39d9f18?, 0xc001e7a480?}, {0x39f7be0?, 0xc001dd3900?})
	/bitnami/blacksmith-sandox/thanos-0.37.2/src/github.com/thanos-io/thanos/internal/cortex/querier/queryrange/roundtrip.go:86 +0x37
github.com/thanos-io/thanos/internal/cortex/querier/queryrange.statsMiddleware.Do({{0x39b8700?, 0xc00096b880?}, 0x1?}, {0x39d9f18, 0xc001e7a480}, {0x39f7be0?, 0xc001dd3900?})
	/bitnami/blacksmith-sandox/thanos-0.37.2/src/github.com/thanos-io/thanos/internal/cortex/querier/queryrange/stats_middleware.go:30 +0x98
github.com/thanos-io/thanos/internal/cortex/querier/queryrange.limitsMiddleware.Do({{0x39dae78?, 0xc0001a0978?}, {0x39b85e0?, 0xc0001a0f30?}}, {0x39d9f18?, 0xc001e4d650?}, {0x39f7be0, 0xc001dd3900})
	/bitnami/blacksmith-sandox/thanos-0.37.2/src/github.com/thanos-io/thanos/internal/cortex/querier/queryrange/limits.go:99 +0x89c
github.com/thanos-io/thanos/internal/cortex/querier/queryrange.roundTripper.RoundTrip({{0x39b8560, 0xc0001a0e28}, {0x39b86e0, 0xc000b59c60}, {0x39deee0, 0xc0001a0b10}, {0xc000abe960, 0x1, 0x1}}, 0xc001e3cb40)
...

Anything else we need to know:

[dosubot]

The panic you're experiencing is likely due to an 'index out of range' error in the AnalyzesMerge function within the queryrange package. This function can cause such a panic when the length of elements is greater than the length of rootElements. The issue arises because the loop iterates over the minimum length of elements and rootElements, but the line rootElements[i].ExecutionTime += analysis[i].ExecutionTime incorrectly uses analysis[i] instead of elements[i]. If analysis has fewer elements than elements, it will result in an 'index out of range' panic ^[1].

To resolve this, you would need to ensure that the correct index is used in the loop to prevent accessing out-of-bounds elements. This might involve modifying the code to correctly reference elements[i] instead of analysis[i].

To continue talking to Dosu, mention @dosu.

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