Harshad Deshmukh created QUICKSTEP-57:
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Summary: FinalizeAggregation Performance Improvement
Key: QUICKSTEP-57
URL: https://issues.apache.org/jira/browse/QUICKSTEP-57
Project: Apache Quickstep
Issue Type: Improvement
Components: Relational Operators, Storage
Reporter: Harshad Deshmukh
Assignee: Harshad Deshmukh
The two step GROUP BY aggregation involves two steps:
1. Aggregation from StorageBlocks in different hash tables. (Performed through
Aggregation operator). The number of hash tables are same as number of worker
threads. Each thread uses only one hash table at a time.
2. Merging the various aggregation hash tables in one (Performed through
Finalize Aggregation operator)
The step 2 is needed because the same GROUP BY key could be present in multiple
hash tables and we need to merge the payloads for the key.
We can avoid the step 2 if the different hash tables mentioned in step 1 have
no overlap in terms of their GROUP BY keys. One way to achieve this is by
partitioning the aggregated tuples based on their GROUP BY keys.
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