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runtime,runtime/metrics: various histogram metrics don't follow the API #43329

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mknyszek opened this issue Dec 22, 2020 · 4 comments
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runtime,runtime/metrics: various histogram metrics don't follow the API #43329

mknyszek opened this issue Dec 22, 2020 · 4 comments
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FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done. release-blocker
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Go1.16

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The metrics /gc/heap/allocs-by-size:bytes, /gc/heap/frees-by-size:bytes, and /gc/pauses:seconds all have issues where the counts don't correctly line up with the buckets.

For the former two, it's the fact that the size classes have inclusive upper-bounds and exclusive lower-bounds while the API expects the opposite. For the latter, it's that the implicit bottom bucket representing the range of values (-inf, 0) isn't actually treated as a real bucket by the implementation. That bucket ends up containing 0-length durations. And there's an extra bucket at the top.

These are minor issues but should be fixed and tested.
@mknyszek mknyszek added NeedsFix The path to resolution is known, but the work has not been done. release-blocker labels Dec 22, 2020
@mknyszek mknyszek added this to the Go1.16 milestone Dec 22, 2020
@mknyszek mknyszek self-assigned this Dec 22, 2020
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Change https://golang.org/cl/279467 mentions this issue: runtime: fix allocs-by-size and frees-by-size buckets

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Change https://golang.org/cl/279468 mentions this issue: runtime: shift timeHistogram buckets and allow negative durations

gopherbot pushed a commit that referenced this issue Dec 23, 2020
@mknyszek
runtime: fix allocs-by-size and frees-by-size buckets
8db7e2f 
Currently these two metrics are reported incorrectly, going by the
documentation in the runtime/metrics package. We just copy in the
size-class-based values from the runtime wholesale, but those implicitly
have an inclusive upper-bound and exclusive lower-bound (e.g. 48-byte
size class contains objects in the size range (32, 48]) but the API
declares inclusive lower-bounds and exclusive upper-bounds.

Also, the bottom bucket representing (-inf, 1) should always be empty.
Extend the consistency check to verify this.

Updates #43329.

Change-Id: I11b5b062a34e13405ab662d15334bda91f779775
Reviewed-on: https://go-review.googlesource.com/c/go/+/279467
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
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