Zoltán Borók-Nagy created IMPALA-12765:
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Summary: Balance consecutive partitions better for Iceberg tables
Key: IMPALA-12765
URL: https://issues.apache.org/jira/browse/IMPALA-12765
Project: IMPALA
Issue Type: Bug
Components: Frontend
Reporter: Zoltán Borók-Nagy
During scheduling Impala does the following:
* Non-Iceberg tables
** The scheduler processes the scan ranges in partition key order
** The scheduler selects N replicas as candidates
** The scheduler chooses the executor from the candidates based on minimum
number of assigned bytes
** So consecutive partitions are more likely to be assigned to different
executors
* Iceberg tables
** The scheduler processes the scan ranges in random order
** The scheduler selects N replicas as candidates
** The scheduler chooses the executor from the candidates based on minimum
number of assigned bytes
** So consecutive partitions (by partition key order) are assigned randomly,
i.e. there's a higher chances of clustering
If the IcebergScanNode ordered its file descriptors based on their paths we
would have a more balanced scheduling for consecutive partitions. Queries that
operate on a range of partitions are quite common, so it makes sense to
optimize that case.
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