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Pre-allocate definition & repetition levels; perf improvement #11675

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Pre-allocate definition & repetition levels; perf improvement #11675

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7f52300
Pre-allocate capacity for definition & repetition levels
theosib-amazon Mar 25, 2022
5e5abc8
Merge pull request #1 from theosib-amazon/theosib-amazon-reserve-levels
theosib-amazon Mar 25, 2022
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6 changes: 4 additions & 2 deletions lib/trino-parquet/src/main/java/io/trino/parquet/reader/PrimitiveColumnReader.java
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Original file line number Diff line number Diff line change
Expand Up @@ -212,8 +212,10 @@ public void prepareNextRead(int batchSize)

public ColumnChunk readPrimitive(Field field)
{
IntList definitionLevels = new IntArrayList();
IntList repetitionLevels = new IntArrayList();
// Pre-allocate these arrays to the necessary size. This saves a substantial amount of
// CPU time by avoiding container resizing.
IntList definitionLevels = new IntArrayList(nextBatchSize);
IntList repetitionLevels = new IntArrayList(nextBatchSize);
seek();
BlockBuilder blockBuilder = field.getType().createBlockBuilder(null, nextBatchSize);
int valueCount = 0;
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