Fix Explain Analyze (#168)

Author: krinart

datafusion-federation/src/optimizer/mod.rs

@@ -191,14 +191,22 @@ impl FederationOptimizerRule {
                 return Ok((None, ScanResult::Distinct(provider)));
             }
 
-            let Some(optimizer) = provider.optimizer() else {
-                // No optimizer provided
-                return Ok((None, ScanResult::None));
-            };
+            // Analyze plans (EXPLAIN ANALYZE) cannot be converted to SQL by
+            // the Unparser, so they must not be federated as a whole. Only the
+            // inner query should be federated; DataFusion's AnalyzeExec will
+            // handle executing it and collecting metrics.
+            if matches!(plan, LogicalPlan::Analyze(_)) {
+                // Fall through to federate children instead.
+            } else {
+                let Some(optimizer) = provider.optimizer() else {
+                    // No optimizer provided
+                    return Ok((None, ScanResult::None));
+                };
 
-            // If this is the root plan node; federate the entire plan
-            let optimized = optimizer.optimize(plan.clone(), _config, |_, _| {})?;
-            return Ok((Some(optimized), ScanResult::None));
+                // If this is the root plan node; federate the entire plan
+                let optimized = optimizer.optimize(plan.clone(), _config, |_, _| {})?;
+                return Ok((Some(optimized), ScanResult::None));
+            }
         }
 
         // The plan is ambiguous; any input that is not yet optimized and has a

datafusion-federation/src/sql/mod.rs

@@ -766,6 +766,57 @@ mod tests {
         Ok(())
     }
 
+    /// EXPLAIN ANALYZE must not federate the Analyze wrapper — only the inner
+    /// query should be federated. Otherwise the SQL Unparser fails because it
+    /// cannot convert Analyze to SQL.
+    #[tokio::test]
+    async fn explain_analyze_not_federated() -> Result<(), DataFusionError> {
+        let executor = TestExecutor {
+            compute_context: "a".into(),
+        };
+
+        let table_ref = "test_table".to_string();
+        let table = get_test_table_provider(table_ref.clone(), executor);
+
+        let state = crate::default_session_state();
+        let ctx = SessionContext::new_with_state(state);
+        ctx.register_table(table_ref, table).unwrap();
+
+        let plan = ctx
+            .sql("EXPLAIN ANALYZE SELECT * FROM test_table")
+            .await?
+            .into_optimized_plan()?;
+
+        // The top-level node must be Analyze, not Federated.
+        assert!(
+            matches!(plan, LogicalPlan::Analyze(_)),
+            "Expected Analyze at root, got: {}",
+            plan.display_indent()
+        );
+
+        // The inner plan should contain a Federated extension node.
+        let mut found_federated = false;
+        plan.apply(|node| {
+            if let LogicalPlan::Extension(ext) = node {
+                if ext.node.name() == "Federated" {
+                    found_federated = true;
+                    return Ok(TreeNodeRecursion::Stop);
+                }
+            }
+            Ok(TreeNodeRecursion::Continue)
+        })?;
+        assert!(
+            found_federated,
+            "Expected a Federated node inside the Analyze plan"
+        );
+
+        // Physical planning should succeed (this is where it used to fail).
+        let physical_plan = ctx.state().create_physical_plan(&plan).await?;
+        assert_eq!(physical_plan.name(), "AnalyzeExec");
+
+        Ok(())
+    }
+
     #[tokio::test]
     async fn sql_query_rewriter_hook_invoked_and_rewrites_sql() -> Result<(), DataFusionError> {
         let executor = TestExecutor {