[jira] [Created] (DRILL-5023) ExternalSortBatch does not spill fully, throws off spill calculations

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

Paul Rogers created DRILL-5023:
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             Summary: ExternalSortBatch does not spill fully, throws off spill calculations
                 Key: DRILL-5023
                 URL: https://issues.apache.org/jira/browse/DRILL-5023
             Project: Apache Drill
          Issue Type: Bug
    Affects Versions: 1.8.0
            Reporter: Paul Rogers
            Priority: Minor


The {{ExternalSortBatch}} (ESB) operator sorts records, spilling to disk as needed to operate within a defined memory budget.

When needed, ESB spills accumulated record batches to disk. However, when doing so, the ESB carves off the first spillable batch and holds it in memory:

{{code}}
    // 1 output container is kept in memory, so we want to hold on to it and transferClone
    // allows keeping ownership
    VectorContainer c1 = VectorContainer.getTransferClone(outputContainer, oContext);
    c1.buildSchema(BatchSchema.SelectionVectorMode.NONE);
    c1.setRecordCount(count);
...
    BatchGroup newGroup = new BatchGroup(c1, fs, outputFile, oContext);
}}

When the spill batch size gets larger (to fix DRILL-5022), the result is that nothing is spilled as the first spillable batch is simply stored back into memory on the (supposedly) spilled batches list.

The desired behavior is for all spillable batches to be written to disk. If the first batch is held back to work around some issue (to keep a schema, say?), then fine a different solution that allows the actual data to spill.



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