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Configure a max limit for lgK values of HLL sketches #15516

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Configure a max limit for lgK values of HLL sketches #15516

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adarshsanjeev
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When using HllSketches, the configured lgK directly relates to the accuracy and resources used. Large values of lgK uses significant amounts of memory for small increases in performance. This PR adds a configurable limit as a runtime property.
This would prevent values of lgK greater than this limit from being allowed.

  • Adds a runtime parameter to configure the maximum allowed value of lgK.

This PR has:

  • been self-reviewed.
  • added documentation for new or modified features or behaviors.
  • a release note entry in the PR description.
  • added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links.
  • added or updated version, license, or notice information in licenses.yaml
  • added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
  • added unit tests or modified existing tests to cover new code paths, ensuring the threshold for code coverage is met.
  • added integration tests.
  • been tested in a test Druid cluster.

@github-actions github-actions bot added Area - Documentation Area - Batch Ingestion Area - MSQ For multi stage queries - https://github.com/apache/druid/issues/12262 labels Dec 8, 2023
@cryptoe
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cryptoe commented Dec 11, 2023

Lets start adding release notes to this running doc created by this PR : #15333

cryptoe
cryptoe reviewed Dec 12, 2023
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docs/development/extensions-core/datasketches-hll.md

|Property| Description| Default |
|--------|------------|------|
|`druid.sketch.config.hllMaxLgK`| The maximum possible value of lgK that HLL sketches can be created with. Useful to limit the maximum lgK in sketches, to avoid the significant usage of resources used by sketches at higher values of lgK. An exception will be thrown if a query configures a lgK value higher than this. This property needs to be set on the broker and middle-manager/indexer. | 20 |
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This should be an ingestion time property only.

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The lgK can be specified during query time as well, wouldn't it need to be limited to avoid running into similar issues?

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@cryptoe cryptoe Feb 1, 2024 •
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I think its more of a ingestion time check only since what we want to avoid is huge rows in the generated segments which increasing the segment sizes which in turn decrease query performance.

cryptoe
cryptoe reviewed Dec 12, 2023
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Left some comments.

cryptoe
cryptoe reviewed Jan 3, 2024
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...ain/java/org/apache/druid/query/aggregation/datasketches/hll/HllSketchAggregatorFactory.java
throw DruidException.forPersona(DruidException.Persona.USER)
.ofCategory(DruidException.Category.INVALID_INPUT)
.build(
"LgK value [%s] for HLL sketch cannot be greater than [%s]. Reduce the lgK value"
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Please mention the name as well.

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github-actions bot commented Apr 2, 2024

This pull request has been marked as stale due to 60 days of inactivity.
It will be closed in 4 weeks if no further activity occurs. If you think
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@github-actions github-actions bot added the stale label Apr 2, 2024
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github-actions bot commented May 1, 2024

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