[v23.2.x] kafka: Add fetch plan and execute latency metric #15129
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Adds a histogram metric to measure the time it takes to create the fetch
plan and execute it - aka a single fetch poll.
It's an approximation for the time it takes to process the data in a
fetch request once it is available.
I have separated two series one which is tracking empty fetches and one
that isn't.
Further the count of the histogram can be used to calculate the ratio of
fetch requests to polls like so:
```
sum(irate(vectorized_kafka_handler_requests_completed_total{...,
handler="fetch"}[$__rate_interval])) by ($aggr_criteria) /
sum(irate(vectorized_fetch_stats_plan_and_execute_latency_us_count{...}[$__rate_interval])) by
($aggr_criteria)
```
Looking at some scenarios we get the following values:
- 500MB/s, 4P/4C, 288P, ~110k batch, 1ms debounce: ~0.37
- 500MB/s, 4P/4C, 288P, ~110k batch, 10ms debounce: ~0.66
- 125MB/s, 8kP/8kC, 40k partitions, 1ms debounce: ~0.012
- 125MB/s, 8kP/8kC, 40k partitions, 10ms debounce: ~0.035
- 125MB/s, 8kP/8kC, 40k partitions, 100ms debounce: ~0.24
(cherry picked from commit 220b11e)
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Failure is:
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ballard26
approved these changes
Nov 27, 2023
piyushredpanda
deleted the
stephan/v232-backport-fetch-plan-execute-metric
branch
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Backport of PR #13485
Fixes #14826