query-frontend 0.17.1: runtime error: index out of range

[arvidsnet]

I faced runtime error: index out of range [7] with length 7 in query-frontend 0.17.1. There were huge amount of such errors (I suppose on each request), attached full log for one such error.
Unfortunately I do not know how to reproduce it, so far it happened only once.
query-frontend-0.17.1.err.log

[yeya24]

Hi, thanks for the report.
I can see this bug here https://github.com/thanos-io/thanos/blob/release-0.17/pkg/store/labelpb/label.go#L310. The Size() is used incorrectly. So this bug happens when the two labelsets we are comparing are exactly the same.

But I am not sure how to reproduce this from the query frontend because before sorting, we use a set to deduplicate series so I expect there is no duplicate labelset.

I will investigate more and check if I miss any corner case

[GiedriusS]

@yeya24 this should be fixed with #3520, right?

[yeya24]

Yes, that's correct. I will close this one.