abhishekrb19 opened a new pull request, #19379:
URL: https://github.com/apache/druid/pull/19379
This PR adds a new `scan` transform type to Druid's transformSpec that
unnests array-valued columns into individual rows during streaming ingestion.
This is similar to the UNNEST support in SQL with MSQ batch ingestion, but
with realtime ingestion.
- New ScanTransform (`type: "scan"`) - a multi-row transform that reuses
the existing `UnnestCursorFactory` / cursor machinery to explode arrays at
ingest time
- Supports multiple scan transforms which can be chained together
- Works with string arrays, object arrays, and nested arrays - objects are
preserved through unnest and queryable via `JSON_VALUE at query time
This would simplify queries by avoiding `UNNEST` and improve query
performance since the 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 with MSQ engine). Multiple scan transforms can be
chained to unnest several array columns.
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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