ORC-562:Don't wrap readerSchema in acidSchema, if readerSchema is alr…

…eady acid

java/core/src/java/org/apache/orc/impl/SchemaEvolution.java

@@ -87,7 +87,8 @@ public SchemaEvolution(TypeDescription fileSchema,
     this.fileSchema = fileSchema;
     this.isAcid = checkAcidSchema(fileSchema);
     this.includeAcidColumns = options.getIncludeAcidColumns();
-    this.readerColumnOffset = isAcid ? acidEventFieldNames.size() : 0;
+    this.readerColumnOffset = (isAcid && readerSchema != null && checkAcidSchema(readerSchema)) || !isAcid
+        ? 0 : acidEventFieldNames.size();
     if (readerSchema != null) {
       if (isAcid) {
         this.readerSchema = createEventSchema(readerSchema);
@@ -614,6 +615,10 @@ public static boolean checkAcidSchema(TypeDescription type) {
    * @return ORC types for the ACID event based on the row's type description
    */
   public static TypeDescription createEventSchema(TypeDescription typeDescr) {
+    // if reader schema is already acid, no need to wrap it in acid schema again
+    if (checkAcidSchema(typeDescr)) {
+      return typeDescr;
+    }
     TypeDescription result = TypeDescription.createStruct()
         .addField("operation", TypeDescription.createInt())
         .addField("originalTransaction", TypeDescription.createLong())