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GH-3246: Clarify the behaviour of big decimal for BYTE_ARRAY #3270

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GH-3246: Clarify the behaviour of big decimal for BYTE_ARRAY #3270

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f8eab28
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ArnavBalyan Aug 18, 2025
b3430d0
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ArnavBalyan Aug 18, 2025
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8 changes: 8 additions & 0 deletions ...-column/src/main/java/org/apache/parquet/column/values/plain/BinaryPlainValuesReader.java
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Expand Up @@ -27,6 +27,14 @@
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
* ValuesReader for variable-length {@code BYTE_ARRAY} columns.
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@wgtmac wgtmac Aug 24, 2025

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I don't think this is the good place to add the comment since this class is for a specific encoding of binary physical type.

As I have replied in the issue, the spec is clear on this so we don't even need the explaination.

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@ArnavBalyan ArnavBalyan Aug 24, 2025

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Thanks for the review, yes on retrospect code comment may not be the best, I'll check if the readme can be made more clear since the user pointed to the readme asking for clarity. Will iterate and get back thanks!

*
* <p>When the column carries the logical type {@code DECIMAL}, the bytes read
* here are the big-endian two's-complement form of the un-scaled integer.
* It slices the requested number of bytes without flipping and
* returns them as a {@link org.apache.parquet.io.api.Binary}.
*/
public class BinaryPlainValuesReader extends ValuesReader {
private static final Logger LOG = LoggerFactory.getLogger(BinaryPlainValuesReader.class);
private ByteBufferInputStream in;
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10 changes: 9 additions & 1 deletion parquet-column/src/main/java/org/apache/parquet/column/values/plain/PlainValuesWriter.java
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Expand Up @@ -32,7 +32,15 @@
import org.slf4j.LoggerFactory;

/**
* Plain encoding except for booleans
* Plain encoding except for booleans.
*
* <p>Endianness note for DECIMAL: when a DECIMAL value is stored in a
* BYTE_ARRAY column, the {@link org.apache.parquet.io.api.Binary}
* passed to this writer already contains the big-endian two's-complement bytes
* of the un-scaled integer (the same bytes produced by
* {@link java.math.BigInteger#toByteArray()}). This writer keeps those bytes
* exactly as they are and only adds the 4-byte little-endian length prefix
* required by the PLAIN encoding. Bytes are not re-ordered.</p>
*/
public class PlainValuesWriter extends ValuesWriter {
private static final Logger LOG = LoggerFactory.getLogger(PlainValuesWriter.class);
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