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Add javadoc on internal UUID format #23961

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Dec 4, 2024
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Add javadoc on internal UUID format #23961

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21 changes: 21 additions & 0 deletions presto-common/src/main/java/com/facebook/presto/common/type/UuidType.java
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Original file line number Diff line number Diff line change
Expand Up @@ -31,6 +31,27 @@
import static java.lang.Long.reverseBytes;
import static java.lang.String.format;

/**
* The value of a UUID is stored as two longs in little-endian
* format in the order of [MSB, LSB] when executing within Presto:
* <br>
*
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Wrapping in a <pre> ... </pre> block might be better

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Suggested change
*
* <pre>

* 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | MSB (LE) | LSB (LE) |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
*
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Suggested change
*
* </pre>

* <br>
* The MSB and LSB are stored in little-endian format because the {@code slice}
* library assumes that longs used in byte-wise comparisons are stored in
* little-endian format. This requires us to store the bytes in little-endian
* too.
* <br>
* On-disk storage specifications such as Parquet or ORC may require different
* endianness or ordering of the MSB and LSB. Such conversions should be done in
* the code responsible for reading and writing the UUID.
*
*/
public class UuidType
extends AbstractPrimitiveType
implements FixedWidthType
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