[SPARK-23378][SQL] move setCurrentDatabase from HiveExternalCatalog to HiveClientImpl

## What changes were proposed in this pull request?

This removes the special case that `alterPartitions` call from `HiveExternalCatalog` can reset the current database in the hive client as a side effect.

## How was this patch tested?

(Please explain how this patch was tested. E.g. unit tests, integration tests, manual tests)
(If this patch involves UI changes, please attach a screenshot; otherwise, remove this)

Please review http://spark.apache.org/contributing.html before opening a pull request.

Author: Feng Liu <[email protected]>

Closes #20564 from liufengdb/move.

Author: Feng Liu

sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveExternalCatalog.scala

@@ -1107,11 +1107,6 @@ private[spark] class HiveExternalCatalog(conf: SparkConf, hadoopConf: Configurat
       }
     }
 
-    // Note: Before altering table partitions in Hive, you *must* set the current database
-    // to the one that contains the table of interest. Otherwise you will end up with the
-    // most helpful error message ever: "Unable to alter partition. alter is not possible."
-    // See HIVE-2742 for more detail.
-    client.setCurrentDatabase(db)
     client.alterPartitions(db, table, withStatsProps)
   }
 

sql/hive/src/main/scala/org/apache/spark/sql/hive/client/HiveClientImpl.scala

@@ -291,14 +291,18 @@ private[hive] class HiveClientImpl(
     state.err = stream
   }
 
-  override def setCurrentDatabase(databaseName: String): Unit = withHiveState {
-    if (databaseExists(databaseName)) {
-      state.setCurrentDatabase(databaseName)
+  private def setCurrentDatabaseRaw(db: String): Unit = {
+    if (databaseExists(db)) {
+      state.setCurrentDatabase(db)
     } else {
-      throw new NoSuchDatabaseException(databaseName)
+      throw new NoSuchDatabaseException(db)
     }
   }
 
+  override def setCurrentDatabase(databaseName: String): Unit = withHiveState {
+    setCurrentDatabaseRaw(databaseName)
+  }
+
   override def createDatabase(
       database: CatalogDatabase,
       ignoreIfExists: Boolean): Unit = withHiveState {
@@ -598,8 +602,18 @@ private[hive] class HiveClientImpl(
       db: String,
       table: String,
       newParts: Seq[CatalogTablePartition]): Unit = withHiveState {
-    val hiveTable = toHiveTable(getTable(db, table), Some(userName))
-    shim.alterPartitions(client, table, newParts.map { p => toHivePartition(p, hiveTable) }.asJava)
+    // Note: Before altering table partitions in Hive, you *must* set the current database
+    // to the one that contains the table of interest. Otherwise you will end up with the
+    // most helpful error message ever: "Unable to alter partition. alter is not possible."
+    // See HIVE-2742 for more detail.
+    val original = state.getCurrentDatabase
+    try {
+      setCurrentDatabaseRaw(db)
+      val hiveTable = toHiveTable(getTable(db, table), Some(userName))
+      shim.alterPartitions(client, table, newParts.map { toHivePartition(_, hiveTable) }.asJava)
+    } finally {
+      state.setCurrentDatabase(original)
+    }
   }
 
   /**