logp: add rate limited logger

[mauri870]

What does this PR do?

This commit adds support for rate limiting to logp.Logger. This is useful
when you have a lot of log messages and you want to avoid flooding the
destination.

The logger was augmented with the following methods:
Throttled will only log once every period.
Sampled will only log the nth message.
Limited will only log the first n messages.

The implementation is based on x/time/rate.Sometimes.

For all these limiters any message that is not logged will be dropped.

These also synergize with one another, for example:

log.Sampled(10).
    Throttled(time.Second).
    Info("")`

will log one message every second, and only one out of ten messages.

Likewise,

log.Limited(10).
    Throttled(time.Second).
    Info("")

will log the first ten messages, and then one message every second.

Why is it important?

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective or that my feature works

Author's Checklist

• [ ]

Related issues

[mauri870]

I really like the idea of a rate limited logger, but I think the cost is too high, at least using the approach implemented here.

For a single threaded execution the cost is tolerable, but for mutli-threaded scenarios the contention is too high for a hot path:

go test -bench='Benchmark.*Logger' -benchmem -run=^$ ./logp | column -t
goos: linux
goarch: amd64
pkg: github.com/elastic/elastic-agent-libs/logp
cpu: Intel(R) Xeon(R) CPU E5-2697A v4 @ 2.60GHz
BenchmarkLogger/default-32                                                                        100000000                                   10.33      ns/op  0         B/op  0  allocs/op
BenchmarkLogger/sampled-32                                                                        17537918                                    69.40      ns/op  0         B/op  0  allocs/op
BenchmarkLogger/throttled-32                                                                      12967281                                    87.35      ns/op  0         B/op  0  allocs/op
BenchmarkLogger/limited-32                                                                        18614289                                    63.58      ns/op  0         B/op  0  allocs/op
BenchmarkConcurrentLoggerSynthetic/default-32                                                     1000000000                                  0.0001241  ns/op  0         B/op  0  allocs/op
BenchmarkConcurrentLoggerSynthetic/sampled-32                                                     277615                                      13437      ns/op  0         B/op  0  allocs/op
BenchmarkConcurrentLoggerSynthetic/throttled-32                                                   236827                                      18124      ns/op  0         B/op  0  allocs/op
BenchmarkConcurrentLoggerSynthetic/limited-32                                                     329881                                      9944       ns/op  0         B/op  0  allocs/op
BenchmarkConcurrentLoggerRealistic/default-32                                                     1000000000                                  0.0000182  ns/op  0         B/op  0  allocs/op
BenchmarkConcurrentLoggerRealistic/sampled-every-4-32                                             347101                                      11292      ns/op  0         B/op  0  allocs/op
BenchmarkConcurrentLoggerRealistic/throttled-1-per-second-32                                      544308                                      12081      ns/op  0         B/op  0  allocs/op
BenchmarkConcurrentLoggerRealistic/limited-first-10-32                                            1051113                                     5290       ns/op  0         B/op  0  allocs/op
BenchmarkConcurrentLoggerRealistic/sampled-1-out-of-2-limited-first-10-throttled-1-per-second-32  290791                                      20145      ns/op  0         B/op  0  allocs/op
PASS                                                                                                                                                           
ok  

[elasticmachine]

💔 Build Failed

• Buildkite Build
• Commit: e60a9c4

Failed CI Steps

• :linux: Test Linux
• :junit: Junit annotate

History

• 💔 Build #544 failed 4455cfe
• 💔 Build #543 failed da8a63c
• 💔 Build #542 failed e10eac5
• 💚 Build #514 succeeded 6d1c976
• 💚 Build #504 succeeded 70036dd

cc @mauri870

[mauri870]

Closing this since the solution is not really what we are looking for right now. We'll continue discussing in elastic/beats#41993.