dongjoon-hyun commented on a change in pull request #31133:
URL: https://github.com/apache/spark/pull/31133#discussion_r570554343



##########
File path: sql/hive/src/main/scala/org/apache/spark/sql/hive/TableReader.scala
##########
@@ -388,6 +393,7 @@ private[hive] object HiveTableUtil {
 private[hive] object DeserializerLock
 
 private[hive] object HadoopTableReader extends HiveInspectors with Logging {
+

Review comment:
       Could you remove this to reduce the diff?

##########
File path: sql/hive/src/main/scala/org/apache/spark/sql/hive/TableReader.scala
##########
@@ -239,7 +240,6 @@ class HadoopTableReader(
       fillPartitionKeys(partValues, mutableRow)
 
       val tableProperties = tableDesc.getProperties
-

Review comment:
       Let's not remove this line~

##########
File path: sql/hive/src/main/scala/org/apache/spark/sql/hive/TableReader.scala
##########
@@ -248,11 +248,16 @@ class HadoopTableReader(
         // SPARK-13709: For SerDes like AvroSerDe, some essential information 
(e.g. Avro schema
         // information) may be defined in table properties. Here we should 
merge table properties
         // and partition properties before initializing the deserializer. Note 
that partition
-        // properties take a higher priority here. For example, a partition 
may have a different
-        // SerDe as the one defined in table properties.
+        // properties take a higher priority here except for the Avro table 
properties
+        // to support schema evolution: in that case the properties given at 
table level will
+        // be used (for details please check SPARK-26836).
+        // For example, a partition may have a different SerDe as the one 
defined in table
+        // properties.
         val props = new Properties(tableProperties)
-        partProps.asScala.foreach {
-          case (key, value) => props.setProperty(key, value)
+        partProps.asScala.filterNot { case (k, _) =>
+          k == AvroTableProperties.SCHEMA_LITERAL.getPropName() && 
tableProperties.containsKey(k)

Review comment:
       `&& tableProperties.containsKey(k)` looks risky to me and beyond this 
PR's test coverage. According to the test case, it looks like `k == 
AvroTableProperties.SCHEMA_LITERAL.getPropName()` is enough to pass the test 
case. Did I understand correctly?

##########
File path: sql/hive/src/main/scala/org/apache/spark/sql/hive/TableReader.scala
##########
@@ -248,11 +248,16 @@ class HadoopTableReader(
         // SPARK-13709: For SerDes like AvroSerDe, some essential information 
(e.g. Avro schema
         // information) may be defined in table properties. Here we should 
merge table properties
         // and partition properties before initializing the deserializer. Note 
that partition
-        // properties take a higher priority here. For example, a partition 
may have a different
-        // SerDe as the one defined in table properties.
+        // properties take a higher priority here except for the Avro table 
properties
+        // to support schema evolution: in that case the properties given at 
table level will
+        // be used (for details please check SPARK-26836).
+        // For example, a partition may have a different SerDe as the one 
defined in table
+        // properties.
         val props = new Properties(tableProperties)
-        partProps.asScala.foreach {
-          case (key, value) => props.setProperty(key, value)
+        partProps.asScala.filterNot { case (k, _) =>
+          k == AvroTableProperties.SCHEMA_LITERAL.getPropName() && 
tableProperties.containsKey(k)

Review comment:
       ~`&& tableProperties.containsKey(k)` looks risky to me and beyond this 
PR's test coverage. According to the test case, it looks like `k == 
AvroTableProperties.SCHEMA_LITERAL.getPropName()` is enough to pass the test 
case. Did I understand correctly?~ My bad. Never mind.

##########
File path: sql/hive/src/main/scala/org/apache/spark/sql/hive/TableReader.scala
##########
@@ -248,11 +249,16 @@ class HadoopTableReader(
         // SPARK-13709: For SerDes like AvroSerDe, some essential information 
(e.g. Avro schema
         // information) may be defined in table properties. Here we should 
merge table properties
         // and partition properties before initializing the deserializer. Note 
that partition
-        // properties take a higher priority here. For example, a partition 
may have a different
-        // SerDe as the one defined in table properties.
+        // properties take a higher priority here except for the Avro table 
properties
+        // to support schema evolution: in that case the properties given at 
table level will
+        // be used (for details please check SPARK-26836).
+        // For example, a partition may have a different SerDe as the one 
defined in table
+        // properties.
         val props = new Properties(tableProperties)
-        partProps.asScala.foreach {
-          case (key, value) => props.setProperty(key, value)
+        partProps.asScala.filterNot { case (k, _) =>
+          k == AvroTableProperties.SCHEMA_LITERAL.getPropName() && 
tableProperties.containsKey(k)
+        }.foreach { case (key, value) =>
+          props.setProperty(key, value)

Review comment:
       Let's revert to the original form like the following. It will make your 
PR content more clear.
   ```scala
   -        }.foreach { case (key, value) =>
   -          props.setProperty(key, value)
   +        }.foreach {
   +          case (key, value) => props.setProperty(key, value)
   ```

##########
File path: 
sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/HiveDDLSuite.scala
##########
@@ -1883,6 +1883,58 @@ class HiveDDLSuite
     }
   }
 
+  test("SPARK-26836: support Avro schema evolution") {

Review comment:
       Could you add an opposite test case which column removal schema 
evolution, please?

##########
File path: 
sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/HiveDDLSuite.scala
##########
@@ -1883,6 +1883,58 @@ class HiveDDLSuite
     }
   }
 
+  test("SPARK-26836: support Avro schema evolution") {

Review comment:
       `Avro` is known to support (1), (2), (3) from the following four.
   ```
    *   1. Add a column
    *   2. Hide a column
    *   3. Change a column position
    *   4. Change a column type (Upcast)
   ```

##########
File path: sql/hive/src/main/scala/org/apache/spark/sql/hive/TableReader.scala
##########
@@ -248,11 +249,16 @@ class HadoopTableReader(
         // SPARK-13709: For SerDes like AvroSerDe, some essential information 
(e.g. Avro schema
         // information) may be defined in table properties. Here we should 
merge table properties
         // and partition properties before initializing the deserializer. Note 
that partition
-        // properties take a higher priority here. For example, a partition 
may have a different
-        // SerDe as the one defined in table properties.
+        // properties take a higher priority here except for the Avro table 
properties
+        // to support schema evolution: in that case the properties given at 
table level will
+        // be used (for details please check SPARK-26836).
+        // For example, a partition may have a different SerDe as the one 
defined in table
+        // properties.
         val props = new Properties(tableProperties)
-        partProps.asScala.foreach {
-          case (key, value) => props.setProperty(key, value)
+        partProps.asScala.filterNot { case (k, _) =>
+          k == AvroTableProperties.SCHEMA_LITERAL.getPropName() && 
tableProperties.containsKey(k)
+        }.foreach { case (key, value) =>
+          props.setProperty(key, value)

Review comment:
       Yes, that one.

##########
File path: 
sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/HiveDDLSuite.scala
##########
@@ -1883,6 +1883,58 @@ class HiveDDLSuite
     }
   }
 
+  test("SPARK-26836: support Avro schema evolution") {

Review comment:
       Sure, take your time~




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