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From paul-rogers <...@git.apache.org>
Subject [GitHub] drill pull request #761: DRILL-5284: Roll-up of final fixes for managed sort
Date Tue, 28 Feb 2017 00:06:45 GMT
Github user paul-rogers commented on a diff in the pull request:

    https://github.com/apache/drill/pull/761#discussion_r103332576
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/physical/impl/xsort/managed/ExternalSortBatch.java
---
    @@ -392,22 +448,31 @@ private void configure(DrillConfig config) {
         // Set too large and the ratio between memory and input data sizes becomes
         // small. Set too small and disk seek times dominate performance.
     
    -    spillBatchSize = config.getBytes(ExecConstants.EXTERNAL_SORT_SPILL_BATCH_SIZE);
    -    spillBatchSize = Math.max(spillBatchSize, MIN_SPILL_BATCH_SIZE);
    +    preferredSpillBatchSize = config.getBytes(ExecConstants.EXTERNAL_SORT_SPILL_BATCH_SIZE);
    +
    +    // In low memory, use no more than 1/4 of memory for each spill batch. Ensures we
    +    // can merge.
    +
    +    preferredSpillBatchSize = Math.min(preferredSpillBatchSize, memoryLimit / 4);
    +
    +    // But, the spill batch should be above some minimum size to prevent complete
    +    // thrashing.
    +
    +    preferredSpillBatchSize = Math.max(preferredSpillBatchSize, MIN_SPILL_BATCH_SIZE);
    --- End diff --
    
    Done later when we tally up memory needs and compare it to available memory. We issue
an error log message if memory overflow is likely. This way, when a query fails, we can look
at the log to see that we knew it would fail due to low memory limits.


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