wuwenw opened a new pull request #7219:
URL: https://github.com/apache/pinot/pull/7219
## Description
Group-by issue: If there are too many groups, then it takes up too much
memory and the garbage collection process becomes a major performance
bottleneck.
Current Approach: When the number of groups reaches a limit (by default
100k), the key generator stops to add new groups.
Produces inaccurate results since we only calculate the first 100k groups
trim on the fly approach: Whenever the number of groups reaches the limit
(by default 100k now), trim the results to 5k using OrderBy information.
- Pays the overhead of orderBy and trimming, so it’s expensive if
the cardinality is relatively low (< 5m), but boost the performance when it’s
large
- Threshold and trim size are configurable
Detailed benchmark number will be added later
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## Upgrade Notes
Does this PR prevent a zero down-time upgrade? (Assume upgrade order:
Controller, Broker, Server, Minion)
* [ ] Yes (Please label as **<code>backward-incompat</code>**, and complete
the section below on Release Notes)
Does this PR fix a zero-downtime upgrade introduced earlier?
* [ ] Yes (Please label this as **<code>backward-incompat</code>**, and
complete the section below on Release Notes)
Does this PR otherwise need attention when creating release notes? Things to
consider:
- New configuration options
- Deprecation of configurations
- Signature changes to public methods/interfaces
- New plugins added or old plugins removed
* [ ] Yes (Please label this PR as **<code>release-notes</code>** and
complete the section on Release Notes)
## Release Notes
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you MUST add text here that you would like to see appear in release notes of
the
next release. -->
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## Documentation
<!-- If you have introduced a new feature or configuration, please add it to
the documentation as well.
See
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