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From jianqiao <...@git.apache.org>
Subject [GitHub] incubator-quickstep issue #179: QUICKSTEP-70-71 Improve aggregation performa...
Date Tue, 07 Feb 2017 20:30:02 GMT
Github user jianqiao commented on the issue:

    https://github.com/apache/incubator-quickstep/pull/179
  
    For the question about `PartitionedHashTablePool` and `HashTablePool`. Note that their
use patterns are different so perhaps it is not natural to merge them into one class.
    
    `PartitionedHashTablePool` creates **a fixed number** of hash tables **on its construction**.
The use pattern is that every `AggregationWorkOrder` updates **all** of these hash tables
and every `FinalizeAggregationWorkOrder` updates one of these hash tables.
    
    `HashTablePool` creates hash tables **on demand**. The current use pattern is that every
`AggregationWorkOrder` checkouts **exclusively** one hash table, updates the hash table, and
returns the hash table back to the pool. Then only one `FinalizeAggregationWorkOrder` is created
to merge all the tables in the pool to the final hash table.


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