Segment reader on the deep store for compute frameworks like Presto and Spark

There are senairos that users need to run complex adhoc queries (e.g. multi-way join with other datasets) or ETL jobs that scan all Pinot segments. Pinot servers are not designed this pattern of workloads. And even we allow this type of scan over the segments, such queries can significant degrade server performance and affect other important online queries.

As an alternative, compute frameworks like Presto and Spark can directly scan the segments stored on Pinot's deep store like HDFS or S3, if there is a segment reader available.

The issue names no files, tests, or entry points. Start by identifying Pinot's segment format and the interfaces needed for compute frameworks such as Presto and Spark to read segments from HDFS or S3. Done means a segment reader can support deep-store scans without routing workloads through Pinot servers.

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