[SPARK-39547][SQL] V2SessionCatalog should not throw NoSuchDatabaseEx…

…ception in loadNamspaceMetadata

### What changes were proposed in this pull request?

This change attempts to make V2SessionCatalog return NoSuchNameSpaceException rather than NoSuchDataseException

### Why are the changes needed?

if a catalog doesn't overrides `namespaceExists` it by default uses `loadNamespaceMetadata` and in case a `db` not exists loadNamespaceMetadata throws a `NoSuchDatabaseException` which is not catched and we see failures even with `if exists` clause. One such use case we observed was in iceberg table a post test clean up was failing with `NoSuchDatabaseException` now. Also queries such as `DROP TABLE IF EXISTS {}` fails with no such db exception.

### Does this PR introduce _any_ user-facing change?

No

### How was this patch tested?

Modified the UT to match the proposed behviour

Closes apache#36948 from singhpk234/fix/loadNamespaceMetadata.

Authored-by: Prashant Singh <psinghvk@amazon.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/v2/V2SessionCatalog.scala

@@ -24,7 +24,7 @@ import scala.collection.JavaConverters._
 import scala.collection.mutable
 
 import org.apache.spark.sql.catalyst.{FunctionIdentifier, SQLConfHelper, TableIdentifier}
-import org.apache.spark.sql.catalyst.analysis.{NoSuchTableException, TableAlreadyExistsException}
+import org.apache.spark.sql.catalyst.analysis.{NoSuchDatabaseException, NoSuchTableException, TableAlreadyExistsException}
 import org.apache.spark.sql.catalyst.catalog.{CatalogDatabase, CatalogTable, CatalogTableType, CatalogUtils, SessionCatalog}
 import org.apache.spark.sql.connector.catalog.{CatalogManager, CatalogV2Util, FunctionCatalog, Identifier, NamespaceChange, SupportsNamespaces, Table, TableCatalog, TableChange, V1Table}
 import org.apache.spark.sql.connector.catalog.NamespaceChange.RemoveProperty
@@ -245,7 +245,12 @@ class V2SessionCatalog(catalog: SessionCatalog)
   override def loadNamespaceMetadata(namespace: Array[String]): util.Map[String, String] = {
     namespace match {
       case Array(db) =>
-        catalog.getDatabaseMetadata(db).toMetadata
+        try {
+          catalog.getDatabaseMetadata(db).toMetadata
+        } catch {
+          case _: NoSuchDatabaseException =>
+            throw QueryCompilationErrors.noSuchNamespaceError(namespace)
+        }
 
       case _ =>
         throw QueryCompilationErrors.noSuchNamespaceError(namespace)

sql/core/src/test/scala/org/apache/spark/sql/execution/command/v1/DescribeNamespaceSuite.scala

@@ -59,5 +59,6 @@ trait DescribeNamespaceSuiteBase extends command.DescribeNamespaceSuiteBase
  * table catalog.
  */
 class DescribeNamespaceSuite extends DescribeNamespaceSuiteBase with CommandSuiteBase {
+  override def notFoundMsgPrefix: String = if (conf.useV1Command) "Database" else "Namespace"
   override def commandVersion: String = super[DescribeNamespaceSuiteBase].commandVersion
 }

sql/core/src/test/scala/org/apache/spark/sql/execution/datasources/v2/V2SessionCatalogSuite.scala

@@ -850,7 +850,7 @@ class V2SessionCatalogNamespaceSuite extends V2SessionCatalogBaseSuite {
   test("loadNamespaceMetadata: fail missing namespace") {
     val catalog = newCatalog()
 
-    val exc = intercept[NoSuchDatabaseException] {
+    val exc = intercept[NoSuchNamespaceException] {
       catalog.loadNamespaceMetadata(testNs)
     }
 

sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/command/DescribeNamespaceSuite.scala

@@ -24,5 +24,6 @@ import org.apache.spark.sql.execution.command.v1
  * table catalog.
  */
 class DescribeNamespaceSuite extends v1.DescribeNamespaceSuiteBase with CommandSuiteBase {
+  override def notFoundMsgPrefix: String = if (conf.useV1Command) "Database" else "Namespace"
   override def commandVersion: String = super[DescribeNamespaceSuiteBase].commandVersion
 }