Add DistributedPlanError::NonDistributable rule and do not distribute SHOW COLUMNS

src/distributed_physical_optimizer_rule.rs

@@ -10,6 +10,7 @@ use datafusion::physical_plan::ExecutionPlanProperties;
 use datafusion::physical_plan::coalesce_partitions::CoalescePartitionsExec;
 use datafusion::physical_plan::joins::{HashJoinExec, PartitionMode};
 use datafusion::physical_plan::sorts::sort_preserving_merge::SortPreservingMergeExec;
+use datafusion::physical_plan::streaming::StreamingTableExec;
 use datafusion::{
     common::tree_node::{Transformed, TreeNode},
     config::ConfigOptions,
@@ -196,7 +197,23 @@ impl DistributedPhysicalOptimizerRule {
     pub fn distribute_plan(
         plan: Arc<dyn ExecutionPlan>,
     ) -> Result<Arc<dyn ExecutionPlan>, DataFusionError> {
-        let stage = Self::_distribute_plan_inner(Uuid::new_v4(), plan, &mut 1, 0, 1)?;
+        let stage = match Self::_distribute_plan_inner(Uuid::new_v4(), plan.clone(), &mut 1, 0, 1) {
+            Ok(stage) => stage,
+            Err(err) => {
+                return match get_distribute_plan_err(&err) {
+                    Some(DistributedPlanError::NonDistributable(_)) => plan
+                        .transform_down(|plan| {
+                            // If the node cannot be distributed, rollback all the network boundaries.
+                            if let Some(nb) = plan.as_network_boundary() {
+                                return Ok(Transformed::yes(nb.rollback()?));
+                            }
+                            Ok(Transformed::no(plan))
+                        })
+                        .map(|v| v.data),
+                    _ => Err(err),
+                };
+            }
+        };
         let plan = stage.plan.decoded()?;
         Ok(Arc::new(DistributedExec::new(Arc::clone(plan))))
     }
@@ -219,6 +236,11 @@ impl DistributedPhysicalOptimizerRule {
                 }
             }
 
+            // We cannot distribute [StreamingTableExec] nodes, so abort distribution.
+            if plan.as_any().is::<StreamingTableExec>() {
+                return Err(non_distributable_err(StreamingTableExec::static_name()))
+            }
+
             if let Some(node) = plan.as_any().downcast_ref::<PartitionIsolatorExec>() {
                 // If there's only 1 task, no need to perform any isolation.
                 if n_tasks == 1 {
@@ -259,6 +281,11 @@ impl DistributedPhysicalOptimizerRule {
                             }
                             dnode = Referenced::Arced(dnode.as_ref().with_input_task_count(*limit)?);
                         }
+                        Some(DistributedPlanError::NonDistributable(_)) => {
+                            // This full plan is non-distributable, so abort any task and stage
+                            // assignation.
+                            return Err(e);
+                        }
                     },
                 }
             };
@@ -376,14 +403,17 @@ enum DistributedPlanError {
     /// Prompts the planner to limit the amount of tasks used in the stage that is currently
     /// being planned.
     LimitTasks(usize),
+    /// Signals the planner that this whole plan is non-distributable. This can happen if
+    /// certain nodes are present, like [StreamingTableExec], which are typically used in
+    /// queries that rather performing some execution, they perform some introspection.
+    NonDistributable(&'static str),
 }
 
 impl Display for DistributedPlanError {
     fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
         match self {
-            DistributedPlanError::LimitTasks(n) => {
-                write!(f, "LimitTasksErr: {n}")
-            }
+            DistributedPlanError::LimitTasks(n) => write!(f, "LimitTasksErr: {n}"),
+            DistributedPlanError::NonDistributable(name) => write!(f, "NonDistributable: {name}"),
         }
     }
 }
@@ -396,6 +426,12 @@ pub fn limit_tasks_err(limit: usize) -> DataFusionError {
     DataFusionError::External(Box::new(DistributedPlanError::LimitTasks(limit)))
 }
 
+/// Builds a [DistributedPlanError::NonDistributable] error. This error prompts the distributed
+/// planner to not distribute the query at all.
+pub fn non_distributable_err(name: &'static str) -> DataFusionError {
+    DataFusionError::External(Box::new(DistributedPlanError::NonDistributable(name)))
+}
+
 fn get_distribute_plan_err(err: &DataFusionError) -> Option<&DistributedPlanError> {
     let DataFusionError::External(err) = err else {
         return None;
@@ -630,6 +666,20 @@ mod tests {
         ");
     }
 
+    #[tokio::test]
+    async fn test_show_columns() {
+        let query = r#"SHOW COLUMNS from weather"#;
+        let plan = sql_to_explain(query, 2).await.unwrap();
+        assert_snapshot!(plan, @r"
+        CoalescePartitionsExec
+          ProjectionExec: expr=[table_catalog@0 as table_catalog, table_schema@1 as table_schema, table_name@2 as table_name, column_name@3 as column_name, data_type@5 as data_type, is_nullable@4 as is_nullable]
+            CoalesceBatchesExec: target_batch_size=8192
+              FilterExec: table_name@2 = weather
+                RepartitionExec: partitioning=RoundRobinBatch(4), input_partitions=1
+                  StreamingTableExec: partition_sizes=1, projection=[table_catalog, table_schema, table_name, column_name, is_nullable, data_type]
+        ");
+    }
+
     async fn sql_to_explain(query: &str, tasks: usize) -> Result<String, DataFusionError> {
         sql_to_explain_with_rule(
             query,
@@ -644,7 +694,9 @@ mod tests {
         query: &str,
         rule: DistributedPhysicalOptimizerRule,
     ) -> Result<String, DataFusionError> {
-        let config = SessionConfig::new().with_target_partitions(4);
+        let config = SessionConfig::new()
+            .with_target_partitions(4)
+            .with_information_schema(true);
 
         let state = SessionStateBuilder::new()
             .with_default_features()

tests/introspection.rs

@@ -0,0 +1,85 @@
+#[cfg(all(feature = "integration", test))]
+mod tests {
+    use datafusion::arrow::util::pretty::pretty_format_batches;
+    use datafusion::execution::SessionStateBuilder;
+    use datafusion::physical_optimizer::PhysicalOptimizerRule;
+    use datafusion::physical_plan::execute_stream;
+    use datafusion::prelude::SessionConfig;
+    use datafusion_distributed::test_utils::localhost::start_localhost_context;
+    use datafusion_distributed::test_utils::parquet::register_parquet_tables;
+    use datafusion_distributed::{
+        DefaultSessionBuilder, DistributedPhysicalOptimizerRule,
+        MappedDistributedSessionBuilderExt, assert_snapshot, display_plan_ascii,
+    };
+    use futures::TryStreamExt;
+    use std::error::Error;
+
+    #[tokio::test]
+    async fn distributed_show_columns() -> Result<(), Box<dyn Error>> {
+        let (ctx, _guard) = start_localhost_context(
+            3,
+            DefaultSessionBuilder.map(|mut v: SessionStateBuilder| {
+                v = v.with_config(SessionConfig::default().with_information_schema(true));
+                Ok(v.build())
+            }),
+        )
+        .await;
+        register_parquet_tables(&ctx).await?;
+
+        let df = ctx.sql(r#"SHOW COLUMNS from weather"#).await?;
+        let physical = df.create_physical_plan().await?;
+        let physical_distributed = DistributedPhysicalOptimizerRule::default()
+            .with_network_shuffle_tasks(2)
+            .with_network_coalesce_tasks(2)
+            .optimize(physical.clone(), &Default::default())?;
+
+        let physical_distributed_str = display_plan_ascii(physical_distributed.as_ref());
+
+        assert_snapshot!(physical_distributed_str,
+            @r"
+        CoalescePartitionsExec
+          ProjectionExec: expr=[table_catalog@0 as table_catalog, table_schema@1 as table_schema, table_name@2 as table_name, column_name@3 as column_name, data_type@5 as data_type, is_nullable@4 as is_nullable]
+            CoalesceBatchesExec: target_batch_size=8192
+              FilterExec: table_name@2 = weather
+                RepartitionExec: partitioning=RoundRobinBatch(3), input_partitions=1
+                  StreamingTableExec: partition_sizes=1, projection=[table_catalog, table_schema, table_name, column_name, is_nullable, data_type]
+        ",
+        );
+
+        let batches_distributed = pretty_format_batches(
+            &execute_stream(physical_distributed, ctx.task_ctx())?
+                .try_collect::<Vec<_>>()
+                .await?,
+        )?;
+        assert_snapshot!(batches_distributed, @r"
+        +---------------+--------------+------------+---------------+-----------+-------------+
+        | table_catalog | table_schema | table_name | column_name   | data_type | is_nullable |
+        +---------------+--------------+------------+---------------+-----------+-------------+
+        | datafusion    | public       | weather    | MinTemp       | Float64   | YES         |
+        | datafusion    | public       | weather    | MaxTemp       | Float64   | YES         |
+        | datafusion    | public       | weather    | Rainfall      | Float64   | YES         |
+        | datafusion    | public       | weather    | Evaporation   | Float64   | YES         |
+        | datafusion    | public       | weather    | Sunshine      | Utf8View  | YES         |
+        | datafusion    | public       | weather    | WindGustDir   | Utf8View  | YES         |
+        | datafusion    | public       | weather    | WindGustSpeed | Utf8View  | YES         |
+        | datafusion    | public       | weather    | WindDir9am    | Utf8View  | YES         |
+        | datafusion    | public       | weather    | WindDir3pm    | Utf8View  | YES         |
+        | datafusion    | public       | weather    | WindSpeed9am  | Utf8View  | YES         |
+        | datafusion    | public       | weather    | WindSpeed3pm  | Int64     | YES         |
+        | datafusion    | public       | weather    | Humidity9am   | Int64     | YES         |
+        | datafusion    | public       | weather    | Humidity3pm   | Int64     | YES         |
+        | datafusion    | public       | weather    | Pressure9am   | Float64   | YES         |
+        | datafusion    | public       | weather    | Pressure3pm   | Float64   | YES         |
+        | datafusion    | public       | weather    | Cloud9am      | Int64     | YES         |
+        | datafusion    | public       | weather    | Cloud3pm      | Int64     | YES         |
+        | datafusion    | public       | weather    | Temp9am       | Float64   | YES         |
+        | datafusion    | public       | weather    | Temp3pm       | Float64   | YES         |
+        | datafusion    | public       | weather    | RainToday     | Utf8View  | YES         |
+        | datafusion    | public       | weather    | RISK_MM       | Float64   | YES         |
+        | datafusion    | public       | weather    | RainTomorrow  | Utf8View  | YES         |
+        +---------------+--------------+------------+---------------+-----------+-------------+
+        ");
+
+        Ok(())
+    }
+}