fix(dnstap source): increase request limit for TCP dnstap source

[esensar]

Summary

Uses max_frame_handling_tasks setting to increase the default request limit. By default, max_frame_handling_tasks is 1000 and since the code for this component only handles 1 event for each permit, this translates well into this usage. This greatly reduces time lost by re-acquiring permits and waiting for connections that produce no data to drop the permits.

Vector configuration

api:
  enabled: true
  address: "0.0.0.0:8686"

sources:
  dnstap_tcp:
    type: "dnstap"
    mode: "tcp"
    address: "0.0.0.0:59001"

sinks:
  console:
    inputs: ["dnstap_tcp"]
    type: "blackhole"

How did you test this PR?

Started Vector with the above configuration, connected (THREAD COUNT - 1) dnstap clients that send no data and then connected 64 more. Observing via vector top, before #23123, this managed 200-300k events/sec, but it often produced errors and crashed connections. After #23123, this scenario dropped to <10k events/sec. After this fix, it is close to the original (still a bit less, but still in 200-300k events/sec range) and no errors appear. This can further be controlled with max_frame_handling_tasks, which is already used in this component - default is 1000, but performance can further be improved, although it doesn't make much difference if it is already higher than connection count.

Change Type

• Bug fix
• New feature
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines.
• No. A maintainer will apply the no-changelog label to this PR.

References

• Closes: Missing or throttled events with dnstap TCP source on v0.48.0 #23392

Notes

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[esensar]

@jszwedko Could this get in before the release? It is a small change, but it prevents the issue that forces some users to use 0.47.0

[pront]

@jszwedko Could this get in before the release? It is a small change, but it prevents the issue that forces some users to use 0.47.0

Hi @esensar, is it ready for review? The release is scheduled for next week but we can probably include this PR.

[esensar]

Sorry, I must have left it a draft by accident. It is ready, I will add a changelog.