abhishekrb19 opened a new pull request, #19379:
URL: https://github.com/apache/druid/pull/19379
This PR adds scan query to Druid's transformSpec that can unnest
array-valued columns into individual rows during streaming ingestion and
possibly do other things that are feasible with scan query semantics. This is
similar to the UNNEST support in SQL with MSQ batch ingestion, but for realtime
ingestion.
- New ScanTransform (type: "scan") — a multi-row transform that wraps an
embedded scan query and reuses the existing ScanQueryEngine, UnnestDataSource
and UnnestCursorFactory machinery to explode arrays at ingest time. Each input
row is wrapped
in a temporary single-row segment, the configured scan query runs against
it, and the resulting rows are emitted downstream.
- The scan query's data source uses "__input__" as the base table, with an
unnest data source to specify which column to explode and an optional
unnestFilter to filter array elements
- Supports string arrays, object arrays, and nested arrays - objects are
preserved through unnest
This simplifies queries by avoiding UNNEST at query time and improves
query performance since unnesting is done once at ingest time rather than
repeatedly at query time.
### Release note
Scan transform for ingestion-time array unnesting. Added a new "scan"
transform type in transformSpec that unnests array-valued columns into
individual rows during streaming ingestion (similar to existing UNNEST
functionality with Druid SQL and the MSQ engine). The scan transform wraps a
scan query with an unnest data source to explode arrays at ingest time.
This PR has:
- [x] been self-reviewed.
- [x] added documentation for new or modified features or behaviors.
- [x] a release note entry in the PR description.
- [x] added Javadocs for most classes and all non-trivial methods. Linked
related entities via Javadoc links.
- [x] added comments explaining the "why" and the intent of the code
wherever would not be obvious for an unfamiliar reader.
- [x] added unit tests or modified existing tests to cover new code paths,
ensuring the threshold for [code
coverage](https://github.com/apache/druid/blob/master/dev/code-review/code-coverage.md)
is met.
- [x] added integration tests.
- [x] been tested in a test Druid cluster.
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