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[WIP] Add sampling histogram #94672

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[WIP] Add sampling histogram #94672

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@MikeSpreitzer MikeSpreitzer commented Sep 10, 2020 •
edited

What type of PR is this?

/kind cleanup

What this PR does / why we need it:
In https://github.com/kubernetes/apiserver/blob/master/pkg/util/flowcontrol/metrics/sample_and_watermark.go today there is the abstraction of sampling a variable to populate a histogram. It has an awkward bit of code: a loop to call the Observe method of a Prometheus Histogram a variable number of times. This led to the suggestion prometheus/client_golang#796 . The discussion there suggested I create a new Prometheus abstraction, possibly out of (prometheus) tree. This PR is my start on such a creation, indeed out of the prometheus tree.

There are three bits of tension here:

  1. The support for "vectors" of metrics in the Prometheus golang library is not public --- and it is non-trivial. This makes doing this work out of the prometheus tree problematic.
  2. sampling-histogram_test.go uses fake clocks. That's the only reasonable way to get sufficient control in a test that runs quickly. But the Prometheus tree does not include such clocks, so moving this code into the Prometheus tree would be problematic.
  3. sample_and_watermark.go traffics in passive clocks (and with good reason: to support event-based testing of API Priority and Fairness code), but k8s.io/utils/clock does not define passive clocks.

Which issue(s) this PR fixes:

Fixes prometheus/client_golang#796

Special notes for your reviewer:
For the moment I put a personal copyright on the code that could go in either Kubernetes or Prometheus, depending on how the relevant tensions are relaxed.

Does this PR introduce a user-facing change?:

NONE

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

@MikeSpreitzer
Start drafting SamplingHistogram
e1e022f 
This covers SamplingHistogram but not SamplingHistogramVec (because
the vec support of prometheus is not public).
@MikeSpreitzer
Added wrapper for SamplingHistogram
93ef341
@k8s-ci-robot k8s-ci-robot added do-not-merge/work-in-progress Indicates that a PR should not merge because it is a work in progress. release-note-none Denotes a PR that doesn't merit a release note. kind/cleanup Categorizes issue or PR as related to cleaning up code, process, or technical debt. size/L Denotes a PR that changes 100-499 lines, ignoring generated files. cncf-cla: yes Indicates the PR's author has signed the CNCF CLA. needs-sig Indicates an issue or PR lacks a `sig/foo` label and requires one. needs-priority Indicates a PR lacks a `priority/foo` label and requires one. labels Sep 10, 2020
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/sig api-machinery

@k8s-ci-robot k8s-ci-robot added sig/api-machinery Categorizes an issue or PR as relevant to SIG API Machinery. sig/cluster-lifecycle Categorizes an issue or PR as relevant to SIG Cluster Lifecycle. sig/instrumentation Categorizes an issue or PR as relevant to SIG Instrumentation. and removed needs-sig Indicates an issue or PR lacks a `sig/foo` label and requires one. labels Sep 10, 2020
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[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: MikeSpreitzer
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@MikeSpreitzer
Add control flow to silence static checker
bbb0cf5 
Before this change, the staticcheck test in the pull-kubernetes-verify
job complained about some possible nil pointer dereferences, but those
would never happen because `t.Errorf` aborts the test.  Added control
flow (that will never be reached, if you understand `t.Errorf`) to
make it obvious that the nil dereferences will never happen.
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k8s-ci-robot commented Sep 12, 2020 •
edited

@MikeSpreitzer: The following test failed, say /retest to rerun all failed tests:

Test name Commit Details Rerun command
pull-kubernetes-verify bbb0cf5 link /test pull-kubernetes-verify

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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@MikeSpreitzer MikeSpreitzer mentioned this pull request Sep 12, 2020
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/test pull-kubernetes-bazel-test

@MikeSpreitzer MikeSpreitzer mentioned this pull request Sep 12, 2020
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This is waiting on prometheus/client_golang#803 to merge.

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kubernetes/utils#190 is going to be important

@MikeSpreitzer MikeSpreitzer mentioned this pull request Oct 8, 2020
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beorn7 commented Oct 15, 2020

prometheus/client_golang#803 is merged now. Sorry for the delay. I'll cut a release v1.8.0 of prometheus/client_golang today so you don't need to lock to a particular commit in your go.mod file anymore.

If you need help with what I said about implementing a more efficient sampling histogram, let me know. For example, I could create a PR on top of this, once it is merged (or even before, if you prefer that).

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/lifecycle stale

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beorn7 commented Jan 13, 2021

As this has gone stale now, let me repeat my offer above to help implementing my suggestion. Let me know if that's something you would appreciate.

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/lifecycle rotten

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/remove-lifecycle rotten
Yes, @beorn7 , thanks for your offer, I am interested. Just a little swamped now and slow on getting things done.

@k8s-ci-robot k8s-ci-robot removed the lifecycle/rotten Denotes an issue or PR that has aged beyond stale and will be auto-closed. label Feb 12, 2021
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beorn7 commented Feb 15, 2021

OK, I'll try to propose something in the next few days.

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beorn7 commented Feb 26, 2021

@MikeSpreitzer I created a PR against your fork to demonstrate my proposal.

@k8s-ci-robot k8s-ci-robot added the needs-rebase Indicates a PR cannot be merged because it has merge conflicts with HEAD. label Apr 6, 2021
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@MikeSpreitzer: PR needs rebase.

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/lifecycle stale

@k8s-ci-robot k8s-ci-robot added the lifecycle/stale Denotes an issue or PR has remained open with no activity and has become stale. label Jul 5, 2021
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/lifecycle rotten

@k8s-ci-robot k8s-ci-robot added lifecycle/rotten Denotes an issue or PR that has aged beyond stale and will be auto-closed. and removed lifecycle/stale Denotes an issue or PR has remained open with no activity and has become stale. labels Aug 4, 2021
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This bot triages issues and PRs according to the following rules:

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/close

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@k8s-triage-robot: Closed this PR.

In response to this:

The Kubernetes project currently lacks enough active contributors to adequately respond to all issues and PRs.

This bot triages issues and PRs according to the following rules:

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/close

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Feature Request: Permit histogram's Observe() method to take an observation count
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