Core: Update metadata location without updating lastUpdatedMillis (#1…

…1151)

Using `TableMetadata.buildFrom(metadata).withMetadataLocation(metadataLocation).build()` would do the following things:
- update `lastUpdatedMillis`
- write a new `metadata-log` entry

However, in `LoadTableResponse` / `RestSessionCatalog` the goal is to only update the metadata location without updating the two mentioned things above.

core/src/main/java/org/apache/iceberg/TableMetadata.java

@@ -966,6 +966,15 @@ private Builder(TableMetadata base) {
 
     public Builder withMetadataLocation(String newMetadataLocation) {
       this.metadataLocation = newMetadataLocation;
+      if (null != base) {
+        // carry over lastUpdatedMillis from base and set previousFileLocation to null to avoid
+        // writing a new metadata log entry
+        // this is safe since setting metadata location doesn't cause any changes and no other
+        // changes can be added when metadata location is configured
+        this.lastUpdatedMillis = base.lastUpdatedMillis();
+        this.previousFileLocation = null;
+      }
+
       return this;
     }
 

core/src/test/java/org/apache/iceberg/TestTableMetadata.java

@@ -1685,4 +1685,38 @@ public void testV3TimestampNanoTypeSupport() {
         ImmutableMap.of(),
         3);
   }
+
+  @Test
+  public void onlyMetadataLocationIsUpdatedWithoutTimestampAndMetadataLogEntry() {
+    String uuid = "386b9f01-002b-4d8c-b77f-42c3fd3b7c9b";
+    TableMetadata metadata =
+        TableMetadata.buildFromEmpty()
+            .assignUUID(uuid)
+            .setLocation("location")
+            .setCurrentSchema(TEST_SCHEMA, 3)
+            .addPartitionSpec(PartitionSpec.unpartitioned())
+            .addSortOrder(SortOrder.unsorted())
+            .discardChanges()
+            .withMetadataLocation("original-metadata-location")
+            .build();
+
+    assertThat(metadata.previousFiles()).isEmpty();
+    assertThat(metadata.metadataFileLocation()).isEqualTo("original-metadata-location");
+
+    // this will only update the metadata location without writing a new metadata log entry or
+    // updating lastUpdatedMillis
+    TableMetadata newMetadata =
+        TableMetadata.buildFrom(metadata).withMetadataLocation("new-metadata-location").build();
+    assertThat(newMetadata.lastUpdatedMillis()).isEqualTo(metadata.lastUpdatedMillis());
+    assertThat(newMetadata.metadataFileLocation()).isEqualTo("new-metadata-location");
+    assertThat(newMetadata.previousFiles()).isEmpty();
+
+    TableMetadata updatedMetadata =
+        TableMetadata.buildFrom(newMetadata)
+            .withMetadataLocation("updated-metadata-location")
+            .build();
+    assertThat(updatedMetadata.lastUpdatedMillis()).isEqualTo(newMetadata.lastUpdatedMillis());
+    assertThat(updatedMetadata.metadataFileLocation()).isEqualTo("updated-metadata-location");
+    assertThat(updatedMetadata.previousFiles()).isEmpty();
+  }
 }