[GitHub] [hudi] n3nash commented on a change in pull request #2424: [HUDI-1509]: Reverting LinkedHashSet changes to fix performance degradation for large schemas

[GitBox <gi...@apache.org>]

n3nash commented on a change in pull request #2424:
URL: https://github.com/apache/hudi/pull/2424#discussion_r555571734



##########
File path: hudi-common/src/main/java/org/apache/hudi/avro/HoodieAvroUtils.java
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@@ -292,53 +284,57 @@ public static GenericRecord stitchRecords(GenericRecord left, GenericRecord righ
     return result;
   }
 
-  /**
-   * Given a avro record with a given schema, rewrites it into the new schema while setting fields only from the old
-   * schema.
-   */
-  public static GenericRecord rewriteRecord(GenericRecord record, Schema newSchema) {
-    return rewrite(record, getCombinedFieldsToWrite(record.getSchema(), newSchema), newSchema);
-  }
-
   /**
    * Given a avro record with a given schema, rewrites it into the new schema while setting fields only from the new
    * schema.
+   * NOTE: Here, the assumption is that you cannot go from an evolved schema (schema with (N) fields)
+   * to an older schema (schema with (N-1) fields). All fields present in the older record schema MUST be present in the
+   * new schema and the default/existing values are carried over.
+   * This particular method does the following things :
+   * a) Create a new empty GenericRecord with the new schema.
+   * b) Set default values for all fields of this transformed schema in the new GenericRecord or copy over the data
+   * from the old schema to the new schema
+   * c) hoodie_metadata_fields have a special treatment. This is done because for code generated AVRO classes
+   * (only HoodieMetadataRecord), the avro record is a SpecificBaseRecord type instead of a GenericRecord.
+   * SpecificBaseRecord throws null pointer exception for record.get(name) if name is not present in the schema of the
+   * record (which happens when converting a SpecificBaseRecord without hoodie_metadata_fields to a new record with.
    */
-  public static GenericRecord rewriteRecordWithOnlyNewSchemaFields(GenericRecord record, Schema newSchema) {
-    return rewrite(record, new LinkedHashSet<>(newSchema.getFields()), newSchema);
-  }
-
-  private static GenericRecord rewrite(GenericRecord record, LinkedHashSet<Field> fieldsToWrite, Schema newSchema) {
+  public static GenericRecord rewriteRecord(GenericRecord oldRecord, Schema newSchema) {
     GenericRecord newRecord = new GenericData.Record(newSchema);
-    for (Schema.Field f : fieldsToWrite) {
-      if (record.get(f.name()) == null) {
+    boolean isSpecificRecord = oldRecord instanceof SpecificRecordBase;
+    for (Schema.Field f : newSchema.getFields()) {
+      if (!isMetadataField(f.name()) && oldRecord.get(f.name()) == null) {
+        // if not metadata field, set defaults
         if (f.defaultVal() instanceof JsonProperties.Null) {
           newRecord.put(f.name(), null);
         } else {
           newRecord.put(f.name(), f.defaultVal());
         }
-      } else {
-        newRecord.put(f.name(), record.get(f.name()));
+      } else if (!isMetadataField(f.name())) {
+        // if not metadata field, copy old value
+        newRecord.put(f.name(), oldRecord.get(f.name()));
+      } else if (!isSpecificRecord) {
+        // if not specific record, copy value for hoodie metadata fields as well

Review comment:
       We don't need to, updated the comments, please take a read and let me know if it's clear 




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