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https://issues.apache.org/jira/browse/DRILL-5026?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15945860#comment-15945860
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Paul Rogers commented on DRILL-5026:
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Primarily a development issue; hard to test at the QA level.
> 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: Sub-task
> Affects Versions: 1.8.0
> Reporter: Paul Rogers
> Assignee: Paul Rogers
> Priority: Minor
> Fix For: 1.11.0
>
>
> 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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