Chinmay Kulkarni created PHOENIX-5362:
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Summary: Mappers should use the queryPlan from the driver rather
than regenerating the plan
Key: PHOENIX-5362
URL: https://issues.apache.org/jira/browse/PHOENIX-5362
Project: Phoenix
Issue Type: Improvement
Reporter: Chinmay Kulkarni
Fix For: 4.15.0
Currently, PhoenixInputFormat#getQueryPlan already generates a queryPlan and we
use this plan to get the scans and splits for the MR job. In
PhoenixInputFormat#createRecordReader which is called inside each mapper, we
again create a queryPlan and pass this to the PhoenixRecordReader instance.
There are multiple problems with this approach:
# The mappers already have information about the scans from the driver code. We
potentially just need to wrap these scans in an iterator and create a
subsequent ResultSet.
# The mappers don't need most of the information embedded within a queryPlan,
so they shouldn't need to regenerate the plan.
# There are weird corner cases that can occur if we replan the query in each
mapper. For ex: If there is an index creation or metadata change in between
when the MR job was created, and when the Mappers actually launch. In this
case, the mappers have the scans created for the first queryPlan, but the
mappers will use iterators created for the second queryPlan. In such cases, the
issued scans would not match the queryPlan embedded in the mappers'
iterators/ResultSet. We could potentially miss some scans/be looking for more
than we actually require since we check the original scans for this size. The
resolved table would be as per the new queryPlan, and there could be a mismatch
here as well (considering the index creation case you mentioned). There are
potentially other repercussions in case of intermediary metadata changes as
well.
Serializing a subset of the information (like the projector, which iterator to
use, etc.) of a QueryPlan and passing it from the driver to the mappers without
having them regenerate the plans seems like the best way forward.
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