[jira] [Created] (DRILL-5026) ExternalSortBatch uses two memory allocators; one will do

["Paul Rogers (JIRA)" <ji...@apache.org>]

Paul Rogers created DRILL-5026:
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             Summary: ExternalSortBatch uses two memory allocators; one will do
                 Key: DRILL-5026
                 URL: https://issues.apache.org/jira/browse/DRILL-5026
             Project: Apache Drill
          Issue Type: Improvement
    Affects Versions: 1.8.0
            Reporter: Paul Rogers
            Priority: Minor


The {{ExternalSortBatch}} (ESB) operator performs a sort while spilling to disk to stay within a defined memory budget.

ESB uses two memory allocators:

* The operator allocator for most operations,
* The copier allocator (child of the operator allocator) for merge operations.

The copier allocator is used only when merging prior to spill.

However, since the ESB must manage within a single memory budget, the code is made more complex by using two allocators, and keeping track of the memory used in both.

Better to use a single allocator. When checking for the need to spill, the code already checks if enough memory is available for an in-memory sort, if needed. Similarly, the code should also check if sufficient memory is available for the copy step when needed.



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