[iceberg] Warn when the Iceberg metadata committer factory is missing from the classpath

paimon-core/src/main/java/org/apache/paimon/iceberg/IcebergCommitCallback.java

@@ -23,6 +23,7 @@
 import org.apache.paimon.data.BinaryRow;
 import org.apache.paimon.data.GenericArray;
 import org.apache.paimon.data.GenericRow;
+import org.apache.paimon.factories.Factory;
 import org.apache.paimon.factories.FactoryException;
 import org.apache.paimon.factories.FactoryUtil;
 import org.apache.paimon.fs.FileStatus;
@@ -165,9 +166,23 @@ public IcebergCommitCallback(FileStoreTable table, String commitUser) {
                     FactoryUtil.discoverFactory(
                             IcebergCommitCallback.class.getClassLoader(),
                             IcebergMetadataCommitterFactory.class,
-                            storageType.toString());
-        } catch (FactoryException ignore) {
+                            storageType.committerFactoryIdentifier());
+        } catch (FactoryException e) {
             metadataCommitterFactory = null;
+            // storage types without a committer have no factory by design, so a miss is expected
+            if (storageType.requiresMetadataCommitter()) {
+                LOG.warn(
+                        "No IcebergMetadataCommitterFactory for '{}={}' found on the classpath, so "
+                                + "table {} will not be synced to the external catalog (commits and "
+                                + "metadata files are unaffected). Check that the module providing it "
+                                + "is deployed and that its META-INF/services/{} entry survived "
+                                + "shading. Cause: {}",
+                        IcebergOptions.METADATA_ICEBERG_STORAGE.key(),
+                        storageType,
+                        table.fullName(),
+                        Factory.class.getName(),
+                        e.getMessage());
+            }
         }
         this.metadataCommitter =
                 metadataCommitterFactory == null ? null : metadataCommitterFactory.create(table);

paimon-core/src/main/java/org/apache/paimon/iceberg/IcebergOptions.java

@@ -198,27 +198,46 @@ public int previousVersionsMax() {
 
     /** Where to store Iceberg metadata. */
     public enum StorageType implements DescribedEnum {
-        DISABLED("disabled", "Disable Iceberg compatibility support."),
-        TABLE_LOCATION("table-location", "Store Iceberg metadata in each table's directory."),
+        DISABLED("disabled", "Disable Iceberg compatibility support.", false),
+        TABLE_LOCATION(
+                "table-location", "Store Iceberg metadata in each table's directory.", false),
         HADOOP_CATALOG(
                 "hadoop-catalog",
                 "Store Iceberg metadata in a separate directory. "
-                        + "This directory can be specified as the warehouse directory of an Iceberg Hadoop catalog."),
+                        + "This directory can be specified as the warehouse directory of an Iceberg Hadoop catalog.",
+                false),
         HIVE_CATALOG(
                 "hive-catalog",
                 "Not only store Iceberg metadata like hadoop-catalog, "
-                        + "but also create Iceberg external table in Hive."),
+                        + "but also create Iceberg external table in Hive.",
+                true),
         REST_CATALOG(
                 "rest-catalog",
                 "Store Iceberg metadata in a REST catalog. "
-                        + "This allows integration with Iceberg REST catalog services.");
+                        + "This allows integration with Iceberg REST catalog services.",
+                true);
 
         private final String value;
         private final String description;
+        private final boolean requiresMetadataCommitter;
 
-        StorageType(String value, String description) {
+        StorageType(String value, String description, boolean requiresMetadataCommitter) {
             this.value = value;
             this.description = description;
+            this.requiresMetadataCommitter = requiresMetadataCommitter;
+        }
+
+        /** Whether this storage type syncs metadata to an external catalog via a committer. */
+        public boolean requiresMetadataCommitter() {
+            return requiresMetadataCommitter;
+        }
+
+        /**
+         * Identifier this storage type's {@code IcebergMetadataCommitterFactory} is registered
+         * under.
+         */
+        public String committerFactoryIdentifier() {
+            return value;
         }
 
         @Override

paimon-hive/paimon-hive-catalog/src/main/java/org/apache/paimon/iceberg/IcebergHiveMetadataCommitterFactory.java

@@ -25,7 +25,7 @@ public class IcebergHiveMetadataCommitterFactory implements IcebergMetadataCommi
 
     @Override
     public String identifier() {
-        return IcebergOptions.StorageType.HIVE_CATALOG.toString();
+        return IcebergOptions.StorageType.HIVE_CATALOG.committerFactoryIdentifier();
     }
 
     @Override

paimon-iceberg/src/main/java/org/apache/paimon/iceberg/IcebergRESTMetadataCommitterFactory.java

@@ -24,7 +24,7 @@
 public class IcebergRESTMetadataCommitterFactory implements IcebergMetadataCommitterFactory {
     @Override
     public String identifier() {
-        return IcebergOptions.StorageType.REST_CATALOG.toString();
+        return IcebergOptions.StorageType.REST_CATALOG.committerFactoryIdentifier();
     }
 
     @Override