Add new user doc to translate logical plan to physical plan (#12026)

* Add new user doc to translate logical plan to physical plan #7306 * prettier * Run doc examples as part of cargo --doc * Update first example to run * Fix next example * fix last example * prettier * clarify table source * prettier * Revert changes --------- Co-authored-by: Andrew Lamb <[email protected]>
apache · Aug 21, 2024 · 78f58c8 · 78f58c8
1 parent 1c7209b
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diff --git a/datafusion/core/src/lib.rs b/datafusion/core/src/lib.rs
@@ -678,6 +678,12 @@ doc_comment::doctest!(
     library_user_guide_sql_api
 );
 
+#[cfg(doctest)]
+doc_comment::doctest!(
+    "../../../docs/source/library-user-guide/building-logical-plans.md",
+    library_user_guide_logical_plans
+);
+
 #[cfg(doctest)]
 doc_comment::doctest!(
     "../../../docs/source/library-user-guide/using-the-dataframe-api.md",

diff --git a/datafusion/expr/src/logical_plan/mod.rs b/datafusion/expr/src/logical_plan/mod.rs
@@ -26,7 +26,7 @@ pub mod tree_node;
 
 pub use builder::{
     build_join_schema, table_scan, union, wrap_projection_for_join_if_necessary,
-    LogicalPlanBuilder, UNNAMED_TABLE,
+    LogicalPlanBuilder, LogicalTableSource, UNNAMED_TABLE,
 };
 pub use ddl::{
     CreateCatalog, CreateCatalogSchema, CreateExternalTable, CreateFunction,

diff --git a/docs/source/library-user-guide/building-logical-plans.md b/docs/source/library-user-guide/building-logical-plans.md
@@ -31,44 +31,52 @@ explained in more detail in the [Query Planning and Execution Overview] section
 DataFusion's [LogicalPlan] is an enum containing variants representing all the supported operators, and also
 contains an `Extension` variant that allows projects building on DataFusion to add custom logical operators.
 
-It is possible to create logical plans by directly creating instances of the [LogicalPlan] enum as follows, but is is
+It is possible to create logical plans by directly creating instances of the [LogicalPlan] enum as shown, but it is
 much easier to use the [LogicalPlanBuilder], which is described in the next section.
 
 Here is an example of building a logical plan directly:
 
-<!-- source for this example is in datafusion_docs::library_logical_plan::plan_1 -->
-
 ```rust
-// create a logical table source
-let schema = Schema::new(vec![
-    Field::new("id", DataType::Int32, true),
-    Field::new("name", DataType::Utf8, true),
-]);
-let table_source = LogicalTableSource::new(SchemaRef::new(schema));
-
-// create a TableScan plan
-let projection = None; // optional projection
-let filters = vec![]; // optional filters to push down
-let fetch = None; // optional LIMIT
-let table_scan = LogicalPlan::TableScan(TableScan::try_new(
-    "person",
-    Arc::new(table_source),
-    projection,
-    filters,
-    fetch,
-)?);
-
-// create a Filter plan that evaluates `id > 500` that wraps the TableScan
-let filter_expr = col("id").gt(lit(500));
-let plan = LogicalPlan::Filter(Filter::try_new(filter_expr, Arc::new(table_scan))?);
-
-// print the plan
-println!("{}", plan.display_indent_schema());
+use datafusion::common::DataFusionError;
+use datafusion::arrow::datatypes::{DataType, Field, Schema, SchemaRef};
+use datafusion::logical_expr::{Filter, LogicalPlan, TableScan, LogicalTableSource};
+use datafusion::prelude::*;
+use std::sync::Arc;
+
+fn main() -> Result<(), DataFusionError> {
+    // create a logical table source
+    let schema = Schema::new(vec![
+        Field::new("id", DataType::Int32, true),
+        Field::new("name", DataType::Utf8, true),
+    ]);
+    let table_source = LogicalTableSource::new(SchemaRef::new(schema));
+
+    // create a TableScan plan
+    let projection = None; // optional projection
+    let filters = vec![]; // optional filters to push down
+    let fetch = None; // optional LIMIT
+    let table_scan = LogicalPlan::TableScan(TableScan::try_new(
+        "person",
+        Arc::new(table_source),
+        projection,
+        filters,
+        fetch,
+        )?
+    );
+
+    // create a Filter plan that evaluates `id > 500` that wraps the TableScan
+    let filter_expr = col("id").gt(lit(500));
+    let plan = LogicalPlan::Filter(Filter::try_new(filter_expr, Arc::new(table_scan)) ? );
+
+    // print the plan
+    println!("{}", plan.display_indent_schema());
+    Ok(())
+}
 ```
 
 This example produces the following plan:
 
-```
+```text
 Filter: person.id > Int32(500) [id:Int32;N, name:Utf8;N]
   TableScan: person [id:Int32;N, name:Utf8;N]
 ```
@@ -78,7 +86,7 @@ Filter: person.id > Int32(500) [id:Int32;N, name:Utf8;N]
 DataFusion logical plans can be created using the [LogicalPlanBuilder] struct. There is also a [DataFrame] API which is
 a higher-level API that delegates to [LogicalPlanBuilder].
 
-The following associated functions can be used to create a new builder:
+There are several functions that can can be used to create a new builder, such as
 
 - `empty` - create an empty plan with no fields
 - `values` - create a plan from a set of literal values
@@ -102,41 +110,107 @@ The following example demonstrates building the same simple query plan as the pr
 <!-- source for this example is in datafusion_docs::library_logical_plan::plan_builder_1 -->
 
 ```rust
-// create a logical table source
-let schema = Schema::new(vec![
-    Field::new("id", DataType::Int32, true),
-    Field::new("name", DataType::Utf8, true),
-]);
-let table_source = LogicalTableSource::new(SchemaRef::new(schema));
-
-// optional projection
-let projection = None;
-
-// create a LogicalPlanBuilder for a table scan
-let builder = LogicalPlanBuilder::scan("person", Arc::new(table_source), projection)?;
-
-// perform a filter operation and build the plan
-let plan = builder
-    .filter(col("id").gt(lit(500)))? // WHERE id > 500
-    .build()?;
-
-// print the plan
-println!("{}", plan.display_indent_schema());
+use datafusion::common::DataFusionError;
+use datafusion::arrow::datatypes::{DataType, Field, Schema, SchemaRef};
+use datafusion::logical_expr::{LogicalPlanBuilder, LogicalTableSource};
+use datafusion::prelude::*;
+use std::sync::Arc;
+
+fn main() -> Result<(), DataFusionError> {
+    // create a logical table source
+    let schema = Schema::new(vec![
+        Field::new("id", DataType::Int32, true),
+        Field::new("name", DataType::Utf8, true),
+    ]);
+    let table_source = LogicalTableSource::new(SchemaRef::new(schema));
+
+    // optional projection
+    let projection = None;
+
+    // create a LogicalPlanBuilder for a table scan
+    let builder = LogicalPlanBuilder::scan("person", Arc::new(table_source), projection)?;
+
+    // perform a filter operation and build the plan
+    let plan = builder
+        .filter(col("id").gt(lit(500)))? // WHERE id > 500
+        .build()?;
+
+    // print the plan
+    println!("{}", plan.display_indent_schema());
+    Ok(())
+}
 ```
 
 This example produces the following plan:
 
-```
+```text
 Filter: person.id > Int32(500) [id:Int32;N, name:Utf8;N]
   TableScan: person [id:Int32;N, name:Utf8;N]
 ```
 
+## Translating Logical Plan to Physical Plan
+
+Logical plans can not be directly executed. They must be "compiled" into an
+[`ExecutionPlan`], which is often referred to as a "physical plan".
+
+Compared to `LogicalPlan`s `ExecutionPlans` have many more details such as
+specific algorithms and detailed optimizations compared to. Given a
+`LogicalPlan` the easiest way to create an `ExecutionPlan` is using
+[`SessionState::create_physical_plan`] as shown below
+
+```rust
+use datafusion::datasource::{provider_as_source, MemTable};
+use datafusion::common::DataFusionError;
+use datafusion::physical_plan::display::DisplayableExecutionPlan;
+use datafusion::arrow::datatypes::{DataType, Field, Schema, SchemaRef};
+use datafusion::logical_expr::{LogicalPlanBuilder, LogicalTableSource};
+use datafusion::prelude::*;
+use std::sync::Arc;
+
+// Creating physical plans may access remote catalogs and data sources
+// thus it must be run with an async runtime.
+#[tokio::main]
+async fn main() -> Result<(), DataFusionError> {
+
+    // create a default table source
+    let schema = Schema::new(vec![
+        Field::new("id", DataType::Int32, true),
+        Field::new("name", DataType::Utf8, true),
+    ]);
+    // To create an ExecutionPlan we must provide an actual
+    // TableProvider. For this example, we don't provide any data
+    // but in production code, this would have `RecordBatch`es with
+    // in memory data
+    let table_provider = Arc::new(MemTable::try_new(Arc::new(schema), vec![])?);
+    // Use the provider_as_source function to convert the TableProvider to a table source
+    let table_source = provider_as_source(table_provider);
+
+    // create a LogicalPlanBuilder for a table scan without projection or filters
+    let logical_plan = LogicalPlanBuilder::scan("person", table_source, None)?.build()?;
+
+    // Now create the physical plan by calling `create_physical_plan`
+    let ctx = SessionContext::new();
+    let physical_plan = ctx.state().create_physical_plan(&logical_plan).await?;
+
+    // print the plan
+    println!("{}", DisplayableExecutionPlan::new(physical_plan.as_ref()).indent(true));
+    Ok(())
+}
+```
+
+This example produces the following physical plan:
+
+```text
+MemoryExec: partitions=0, partition_sizes=[]
+```
+
 ## Table Sources
 
-The previous example used a [LogicalTableSource], which is used for tests and documentation in DataFusion, and is also
-suitable if you are using DataFusion to build logical plans but do not use DataFusion's physical planner. However, if you
-want to use a [TableSource] that can be executed in DataFusion then you will need to use [DefaultTableSource], which is a
-wrapper for a [TableProvider].
+The previous examples use a [LogicalTableSource], which is used for tests and documentation in DataFusion, and is also
+suitable if you are using DataFusion to build logical plans but do not use DataFusion's physical planner.
+
+However, it is more common to use a [TableProvider]. To get a [TableSource] from a
+[TableProvider], use [provider_as_source] or [DefaultTableSource].
 
 [query planning and execution overview]: https://docs.rs/datafusion/latest/datafusion/index.html#query-planning-and-execution-overview
 [architecture guide]: https://docs.rs/datafusion/latest/datafusion/index.html#architecture
@@ -145,5 +219,8 @@ wrapper for a [TableProvider].
 [dataframe]: using-the-dataframe-api.md
 [logicaltablesource]: https://docs.rs/datafusion-expr/latest/datafusion_expr/logical_plan/builder/struct.LogicalTableSource.html
 [defaulttablesource]: https://docs.rs/datafusion/latest/datafusion/datasource/default_table_source/struct.DefaultTableSource.html
+[provider_as_source]: https://docs.rs/datafusion/latest/datafusion/datasource/default_table_source/fn.provider_as_source.html
 [tableprovider]: https://docs.rs/datafusion/latest/datafusion/datasource/provider/trait.TableProvider.html
 [tablesource]: https://docs.rs/datafusion-expr/latest/datafusion_expr/trait.TableSource.html
+[`executionplan`]: https://docs.rs/datafusion/latest/datafusion/physical_plan/trait.ExecutionPlan.html
+[`sessionstate::create_physical_plan`]: https://docs.rs/datafusion/latest/datafusion/execution/session_state/struct.SessionState.html#method.create_physical_plan