Configuration for dropping non-sampled transactions

[axw]

Motivation/summary

Introduce configuration to drop non-sampled transactions. Typically this should only be used in conjunction with transaction aggregation. Off by default for backwards compatibility.

TODO:

- [ ] Docs (will document later, when we have UI support)

• System test
• Log warning if aggregation is not enabled
• Monitoring -- increment counter if non-sampled transaction docs are dropped
• Changelog

Checklist

• I have signed the Contributor License Agreement.
• My code follows the style guidelines of this project (run make check-full for static code checks and linting)
• I have rebased my changes on top of the latest master branch
  - [ ] I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have updated CHANGELOG.asciidoc

How to test these changes

1. Configure an agent with <100% sampling rate
2. Configure server with apm-server.sampling.keep_non_sampled=false
3. Create some transactions
4. Observe that only sampled transactions are recorded

Related issues

Relates to #3485

[ghost]

💚 Build Succeeded

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Build stats

• Build Cause: [Pull request Configuration for dropping non-sampled transactions #3702 updated]

• Start Time: 2020-05-03T03:50:40.438+0000

• Duration: 50 min 13 sec (3012607)

• Commit: 25b90eb

Test stats 🧪

Test	Results
Failed	0
Passed	3005
Skipped	142
Total	3147

Steps errors

Expand to view the steps failures

• Name: Test Sync

  • Description: ./script/jenkins/sync.sh

  • Result: FAILURE

  • Duration: 3 min 53 sec<

  • Start Time: 2020-05-03T04:02:09.309+0000

[jalvz]

Maybe its just me, but I find unsampled (a valid English word afaik) easier to read than non sampled.

[axw]

Maybe its just me, but I find unsampled (a valid English word afaik) easier to read than non sampled.

AFAICT (checked a couple of dictionaries :)), unsampled is not a real word. However, it is reasonably common in this space, so I'll change to it.