Feature/spark disable create table in default db

docs/generated/spark_catalog_configuration.html

@@ -38,6 +38,12 @@
             <td>String</td>
             <td>The default database name.</td>
         </tr>
+        <tr>
+            <td><h5>disable-create-table-in-default-db</h5></td>
+            <td style="word-wrap: break-word;">false</td>
+            <td>Boolean</td>
+            <td>If true, creating table in default database is not allowed and the default database will not be automatically created during catalog initialization.</td>
+        </tr>
         <tr>
             <td><h5>v1Function.enabled</h5></td>
             <td style="word-wrap: break-word;">true</td>

paimon-spark/paimon-spark-common/src/main/java/org/apache/paimon/spark/SparkCatalog.java

@@ -99,6 +99,7 @@
 import static org.apache.paimon.CoreOptions.TYPE;
 import static org.apache.paimon.TableType.FORMAT_TABLE;
 import static org.apache.paimon.spark.SparkCatalogOptions.DEFAULT_DATABASE;
+import static org.apache.paimon.spark.SparkCatalogOptions.DISABLE_CREATE_TABLE_IN_DEFAULT_DB;
 import static org.apache.paimon.spark.SparkCatalogOptions.V1FUNCTION_ENABLED;
 import static org.apache.paimon.spark.SparkTypeUtils.CURRENT_DEFAULT_COLUMN_METADATA_KEY;
 import static org.apache.paimon.spark.SparkTypeUtils.toPaimonType;
@@ -129,6 +130,7 @@ public class SparkCatalog extends SparkBaseCatalog
 
     private Catalog catalog;
     private String defaultDatabase;
+    private boolean disableCreateTableInDefaultDatabase;
     private boolean v1FunctionEnabled;
     @Nullable private PaimonV1FunctionRegistry v1FunctionRegistry;
 
@@ -144,22 +146,28 @@ public void initialize(String name, CaseInsensitiveStringMap options) {
         this.catalog = CatalogFactory.createCatalog(catalogContext);
         this.defaultDatabase =
                 options.getOrDefault(DEFAULT_DATABASE.key(), DEFAULT_DATABASE.defaultValue());
+        this.disableCreateTableInDefaultDatabase =
+                options.getBoolean(
+                        DISABLE_CREATE_TABLE_IN_DEFAULT_DB.key(),
+                        DISABLE_CREATE_TABLE_IN_DEFAULT_DB.defaultValue());
         this.v1FunctionEnabled =
                 options.getBoolean(V1FUNCTION_ENABLED.key(), V1FUNCTION_ENABLED.defaultValue())
                         && DelegateCatalog.rootCatalog(catalog) instanceof RESTCatalog;
         if (v1FunctionEnabled) {
             this.v1FunctionRegistry = new PaimonV1FunctionRegistry(sparkSession);
         }
-        try {
-            catalog.getDatabase(defaultDatabase);
-        } catch (Catalog.DatabaseNotExistException e) {
-            LOG.info(
-                    "Default database '{}' does not exist, caused by: {}, start to create it",
-                    defaultDatabase,
-                    ExceptionUtils.stringifyException(e));
+        if (!disableCreateTableInDefaultDatabase) {
             try {
-                createNamespace(defaultNamespace(), new HashMap<>());
-            } catch (NamespaceAlreadyExistsException ignored) {
+                catalog.getDatabase(defaultDatabase);
+            } catch (Catalog.DatabaseNotExistException e) {
+                LOG.info(
+                        "Default database '{}' does not exist, caused by: {}, start to create it",
+                        defaultDatabase,
+                        ExceptionUtils.stringifyException(e));
+                try {
+                    createNamespace(defaultNamespace(), new HashMap<>());
+                } catch (NamespaceAlreadyExistsException ignored) {
+                }
             }
         }
     }
@@ -374,6 +382,12 @@ public org.apache.spark.sql.connector.catalog.Table createTable(
             Transform[] partitions,
             Map<String, String> properties)
             throws TableAlreadyExistsException, NoSuchNamespaceException {
+        if (disableCreateTableInDefaultDatabase
+                && ident.namespace().length == 1
+                && ident.namespace()[0].equals(defaultDatabase)) {
+            throw new UnsupportedOperationException(
+                    "Creating table in default database is disabled, please specify a database name.");
+        }
         try {
             catalog.createTable(
                     toIdentifier(ident, catalogName),

paimon-spark/paimon-spark-common/src/main/java/org/apache/paimon/spark/SparkCatalogOptions.java

@@ -38,6 +38,14 @@ public class SparkCatalogOptions {
                     .defaultValue(Catalog.DEFAULT_DATABASE)
                     .withDescription("The default database name.");
 
+    public static final ConfigOption<Boolean> DISABLE_CREATE_TABLE_IN_DEFAULT_DB =
+            key("disable-create-table-in-default-db")
+                    .booleanType()
+                    .defaultValue(false)
+                    .withDescription(
+                            "If true, creating table in default database is not allowed "
+                                    + "and the default database will not be automatically created during catalog initialization.");
+
     public static final ConfigOption<Boolean> V1FUNCTION_ENABLED =
             key("v1Function.enabled")
                     .booleanType()

paimon-spark/paimon-spark-ut/src/test/java/org/apache/paimon/spark/SparkCatalogDisableDefaultDbTest.java

@@ -0,0 +1,145 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.paimon.spark;
+
+import org.apache.paimon.fs.Path;
+import org.apache.paimon.spark.extensions.PaimonSparkSessionExtensions;
+
+import org.apache.spark.sql.SparkSession;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatCode;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+/** Tests for {@code disable-create-table-in-default-db} option in Spark. */
+public class SparkCatalogDisableDefaultDbTest {
+
+    private SparkSession spark;
+
+    @AfterEach
+    public void stopSpark() {
+        if (spark != null) {
+            spark.stop();
+            spark = null;
+        }
+    }
+
+    @Test
+    public void testDisableCreateTableInDefaultDb(@TempDir java.nio.file.Path tempDir) {
+        Path warehousePath = new Path("file:" + tempDir.toString());
+        spark =
+                SparkSession.builder()
+                        .master("local[2]")
+                        .config("spark.sql.catalog.paimon", SparkCatalog.class.getName())
+                        .config("spark.sql.catalog.paimon.warehouse", warehousePath.toString())
+                        .config(
+                                "spark.sql.catalog.paimon.disable-create-table-in-default-db",
+                                "true")
+                        .config(
+                                "spark.sql.extensions",
+                                PaimonSparkSessionExtensions.class.getName())
+                        .getOrCreate();
+
+        // Creating table in default database should fail
+        assertThatThrownBy(
+                        () ->
+                                spark.sql(
+                                        "CREATE TABLE paimon.default.t1 (a INT, b STRING) USING paimon"))
+                .hasMessageContaining(
+                        "Creating table in default database is disabled, please specify a database name.");
+
+        // Creating a non-default database should succeed
+        assertThatCode(() -> spark.sql("CREATE DATABASE paimon.my_db")).doesNotThrowAnyException();
+
+        // Creating table in a non-default database should succeed
+        assertThatCode(
+                        () ->
+                                spark.sql(
+                                        "CREATE TABLE paimon.my_db.t1 (a INT, b STRING) USING paimon"))
+                .doesNotThrowAnyException();
+
+        // Verify the table is accessible
+        spark.sql("INSERT INTO paimon.my_db.t1 VALUES (1, 'hello')").collect();
+        assertThat(
+                        spark.sql("SELECT * FROM paimon.my_db.t1").collectAsList().stream()
+                                .map(Object::toString))
+                .containsExactly("[1,hello]");
+    }
+
+    @Test
+    public void testDisableCreateTableWithCustomDefaultDb(@TempDir java.nio.file.Path tempDir) {
+        Path warehousePath = new Path("file:" + tempDir.toString());
+        spark =
+                SparkSession.builder()
+                        .master("local[2]")
+                        .config("spark.sql.catalog.paimon", SparkCatalog.class.getName())
+                        .config("spark.sql.catalog.paimon.warehouse", warehousePath.toString())
+                        .config(
+                                "spark.sql.catalog.paimon.disable-create-table-in-default-db",
+                                "true")
+                        .config("spark.sql.catalog.paimon.defaultDatabase", "custom_default")
+                        .config(
+                                "spark.sql.extensions",
+                                PaimonSparkSessionExtensions.class.getName())
+                        .getOrCreate();
+
+        // Creating table in custom default database should fail
+        assertThatThrownBy(
+                        () ->
+                                spark.sql(
+                                        "CREATE TABLE paimon.custom_default.t1 (a INT, b STRING) USING paimon"))
+                .hasMessageContaining(
+                        "Creating table in default database is disabled, please specify a database name.");
+
+        // Creating a different database and table should succeed
+        assertThatCode(() -> spark.sql("CREATE DATABASE paimon.other_db"))
+                .doesNotThrowAnyException();
+        assertThatCode(
+                        () ->
+                                spark.sql(
+                                        "CREATE TABLE paimon.other_db.t1 (a INT, b STRING) USING paimon"))
+                .doesNotThrowAnyException();
+    }
+
+    @Test
+    public void testDefaultDatabaseNotCreatedWhenDisabled(@TempDir java.nio.file.Path tempDir) {
+        Path warehousePath = new Path("file:" + tempDir.toString());
+        spark =
+                SparkSession.builder()
+                        .master("local[2]")
+                        .config("spark.sql.catalog.paimon", SparkCatalog.class.getName())
+                        .config("spark.sql.catalog.paimon.warehouse", warehousePath.toString())
+                        .config(
+                                "spark.sql.catalog.paimon.disable-create-table-in-default-db",
+                                "true")
+                        .config(
+                                "spark.sql.extensions",
+                                PaimonSparkSessionExtensions.class.getName())
+                        .getOrCreate();
+
+        // Default database should not have been auto-created
+        assertThat(
+                        spark.sql("SHOW DATABASES IN paimon").collectAsList().stream()
+                                .map(r -> r.getString(0)))
+                .doesNotContain("default");
+    }
+}