[GitHub] [hudi] xiarixiaoyao commented on a diff in pull request #8380: [HUDI-6033] Fix rounding exception when to decimal casting

["xiarixiaoyao (via GitHub)" <gi...@apache.org>]

xiarixiaoyao commented on code in PR #8380:
URL: https://github.com/apache/hudi/pull/8380#discussion_r1166535195


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hudi-common/src/main/java/org/apache/hudi/avro/HoodieAvroUtils.java:
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@@ -1040,6 +1035,32 @@ private static Object rewritePrimaryTypeWithDiffSchemaType(Object oldValue, Sche
     throw new AvroRuntimeException(String.format("cannot support rewrite value for schema type: %s since the old schema type is: %s", newSchema, oldSchema));
   }
 
+  /**
+   * When there is a lost in scale, rounding is required to be performed when performing casts.
+   * For types that have a fix scale, the results of the cast will need to be the same for COW and MOR.
+   * <p>
+   * NOTE: COW uses Spark's default rounding of HALF_UP (if Spark entry points are used).
+   * <p>
+   * Floating point types are not considered here as they are susceptible to floating point rounding errors.
+   * <p>
+   * Summary:
+   * <ul>
+   *   <li>double/string -> decimal: HALF_UP</li>
+   *   <li>float -> decimal: HALF_EVEN</li>
+   * </ul>

Review Comment:
   spark always use HALF_UP to cast  FractionalType（float/double） to DecimalType
   why we use HAL_EVEN to cast float -> decimal     
   BTW  hive/presto also use HALF_UP 



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