Stream CSV file during schema inference

datafusion/core/src/datasource/file_format/csv.rs

@@ -19,16 +19,17 @@
 
 use std::any::Any;
 
+use std::collections::HashSet;
 use std::sync::Arc;
 
-use arrow::datatypes::Schema;
+use arrow::datatypes::{DataType, Field, Schema};
 use arrow::{self, datatypes::SchemaRef};
 use async_trait::async_trait;
 use bytes::Buf;
 
 use datafusion_common::DataFusionError;
 
-use futures::TryFutureExt;
+use futures::{pin_mut, StreamExt, TryStreamExt};
 use object_store::{ObjectMeta, ObjectStore};
 
 use super::FileFormat;
@@ -37,7 +38,9 @@ use crate::datasource::file_format::DEFAULT_SCHEMA_INFER_MAX_RECORD;
 use crate::error::Result;
 use crate::execution::context::SessionState;
 use crate::logical_expr::Expr;
-use crate::physical_plan::file_format::{CsvExec, FileScanConfig};
+use crate::physical_plan::file_format::{
+    newline_delimited_stream, CsvExec, FileScanConfig,
+};
 use crate::physical_plan::ExecutionPlan;
 use crate::physical_plan::Statistics;
 
@@ -122,27 +125,75 @@ impl FileFormat for CsvFormat {
 
         let mut records_to_read = self.schema_infer_max_rec.unwrap_or(usize::MAX);
 
-        for object in objects {
-            let data = store
+        'iterating_objects: for object in objects {
+            // stream to only read as many rows as needed into memory
+            let stream = store
                 .get(&object.location)
-                .and_then(|r| r.bytes())
-                .await
-                .map_err(|e| DataFusionError::External(Box::new(e)))?;
-
-            let decoder = self.file_compression_type.convert_read(data.reader())?;
-            let (schema, records_read) = arrow::csv::reader::infer_reader_schema(
-                decoder,
-                self.delimiter,
-                Some(records_to_read),
-                self.has_header,
-            )?;
-            schemas.push(schema.clone());
-            if records_read == 0 {
-                continue;
+                .await?
+                .into_stream()
+                .map_err(|e| DataFusionError::External(Box::new(e)));
+            let stream = newline_delimited_stream(stream);
+            pin_mut!(stream);
+
+            let mut column_names = vec![];
+            let mut column_type_possibilities = vec![];
+            let mut first_chunk = true;
+
+            'reading_object: while let Some(data) = stream.next().await.transpose()? {
+                let (Schema { fields, .. }, records_read) =
+                    arrow::csv::reader::infer_reader_schema(
+                        self.file_compression_type.convert_read(data.reader())?,
+                        self.delimiter,
+                        Some(records_to_read),
+                        // only consider header for first chunk
+                        self.has_header && first_chunk,
+                    )?;
+                records_to_read -= records_read;
+
+                if first_chunk {
+                    // set up initial structures for recording inferred schema across chunks
+                    (column_names, column_type_possibilities) = fields
+                        .into_iter()
+                        .map(|field| {
+                            let mut possibilities = HashSet::new();
+                            if records_read > 0 {
+                                // at least 1 data row read, record the inferred datatype
+                                possibilities.insert(field.data_type().clone());
+                            }
+                            (field.name().clone(), possibilities)
+                        })
+                        .unzip();
+                    first_chunk = false;
+                } else {
+                    if fields.len() != column_type_possibilities.len() {
+                        return Err(DataFusionError::Execution(
+                            format!(
+                                "Encountered unequal lengths between records on CSV file whilst inferring schema. \
+                                    Expected {} records, found {} records",
+                                    column_type_possibilities.len(),
+                                fields.len()
+                            )
+                        ));
+                    }
+
+                    column_type_possibilities.iter_mut().zip(fields).for_each(
+                        |(possibilities, field)| {
+                            possibilities.insert(field.data_type().clone());
+                        },
+                    );
+                }
+
+                if records_to_read == 0 {
+                    break 'reading_object;
+                }
             }
-            records_to_read -= records_read;
+
+            schemas.push(build_schema_helper(
+                column_names,
+                &column_type_possibilities,
+            ));
             if records_to_read == 0 {
-                break;
+                break 'iterating_objects;
             }
         }
 
@@ -176,14 +227,50 @@ impl FileFormat for CsvFormat {
     }
 }
 
+fn build_schema_helper(names: Vec<String>, types: &[HashSet<DataType>]) -> Schema {
+    let fields = names
+        .into_iter()
+        .zip(types)
+        .map(|(field_name, data_type_possibilities)| {
+            // ripped from arrow::csv::reader::infer_reader_schema_with_csv_options
+            // determine data type based on possible types
+            // if there are incompatible types, use DataType::Utf8
+            match data_type_possibilities.len() {
+                1 => Field::new(
+                    field_name,
+                    data_type_possibilities.iter().next().unwrap().clone(),
+                    true,
+                ),
+                2 => {
+                    if data_type_possibilities.contains(&DataType::Int64)
+                        && data_type_possibilities.contains(&DataType::Float64)
+                    {
+                        // we have an integer and double, fall down to double
+                        Field::new(field_name, DataType::Float64, true)
+                    } else {
+                        // default to Utf8 for conflicting datatypes (e.g bool and int)
+                        Field::new(field_name, DataType::Utf8, true)
+                    }
+                }
+                _ => Field::new(field_name, DataType::Utf8, true),
+            }
+        })
+        .collect();
+    Schema::new(fields)
+}
+
 #[cfg(test)]
 mod tests {
     use super::super::test_util::scan_format;
     use super::*;
+    use crate::datasource::file_format::test_util::VariableStream;
     use crate::physical_plan::collect;
     use crate::prelude::{SessionConfig, SessionContext};
+    use bytes::Bytes;
+    use chrono::DateTime;
     use datafusion_common::cast::as_string_array;
     use futures::StreamExt;
+    use object_store::path::Path;
 
     #[tokio::test]
     async fn read_small_batches() -> Result<()> {
@@ -291,6 +378,57 @@ mod tests {
         Ok(())
     }
 
+    #[tokio::test]
+    async fn test_infer_schema_stream() -> Result<()> {
+        let session_ctx = SessionContext::new();
+        let state = session_ctx.state();
+        let variable_object_store =
+            Arc::new(VariableStream::new(Bytes::from("1,2,3,4,5\n"), 200));
+        let object_meta = ObjectMeta {
+            location: Path::parse("/")?,
+            last_modified: DateTime::default(),
+            size: usize::MAX,
+        };
+
+        let num_rows_to_read = 100;
+        let csv_format = CsvFormat {
+            has_header: false,
+            schema_infer_max_rec: Some(num_rows_to_read),
+            ..Default::default()
+        };
+        let inferred_schema = csv_format
+            .infer_schema(
+                &state,
+                &(variable_object_store.clone() as Arc<dyn ObjectStore>),
+                &[object_meta],
+            )
+            .await?;
+
+        let actual_fields: Vec<_> = inferred_schema
+            .fields()
+            .iter()
+            .map(|f| format!("{}: {:?}", f.name(), f.data_type()))
+            .collect();
+        assert_eq!(
+            vec![
+                "column_1: Int64",
+                "column_2: Int64",
+                "column_3: Int64",
+                "column_4: Int64",
+                "column_5: Int64"
+            ],
+            actual_fields
+        );
+        // ensuring on csv infer that it won't try to read entire file
+        // should only read as many rows as was configured in the CsvFormat
+        assert_eq!(
+            num_rows_to_read,
+            variable_object_store.get_iterations_detected()
+        );
+
+        Ok(())
+    }
+
     async fn get_exec(
         state: &SessionState,
         file_name: &str,

datafusion/core/src/datasource/file_format/mod.rs

@@ -87,11 +87,20 @@ pub trait FileFormat: Send + Sync + fmt::Debug {
 
 #[cfg(test)]
 pub(crate) mod test_util {
+    use std::ops::Range;
+    use std::sync::Mutex;
+
     use super::*;
     use crate::datasource::listing::PartitionedFile;
     use crate::datasource::object_store::ObjectStoreUrl;
     use crate::test::object_store::local_unpartitioned_file;
+    use bytes::Bytes;
+    use futures::stream::BoxStream;
+    use futures::StreamExt;
     use object_store::local::LocalFileSystem;
+    use object_store::path::Path;
+    use object_store::{GetResult, ListResult, MultipartId};
+    use tokio::io::AsyncWrite;
 
     pub async fn scan_format(
         state: &SessionState,
@@ -136,4 +145,121 @@ pub(crate) mod test_util {
             .await?;
         Ok(exec)
     }
+
+    /// Mock ObjectStore to provide an variable stream of bytes on get
+    /// Able to keep track of how many iterations of the provided bytes were repeated
+    #[derive(Debug)]
+    pub struct VariableStream {
+        bytes_to_repeat: Bytes,
+        max_iterations: usize,
+        iterations_detected: Arc<Mutex<usize>>,
+    }
+
+    impl std::fmt::Display for VariableStream {
+        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            write!(f, "VariableStream")
+        }
+    }
+
+    #[async_trait]
+    impl ObjectStore for VariableStream {
+        async fn put(&self, _location: &Path, _bytes: Bytes) -> object_store::Result<()> {
+            unimplemented!()
+        }
+
+        async fn put_multipart(
+            &self,
+            _location: &Path,
+        ) -> object_store::Result<(MultipartId, Box<dyn AsyncWrite + Unpin + Send>)>
+        {
+            unimplemented!()
+        }
+
+        async fn abort_multipart(
+            &self,
+            _location: &Path,
+            _multipart_id: &MultipartId,
+        ) -> object_store::Result<()> {
+            unimplemented!()
+        }
+
+        async fn get(&self, _location: &Path) -> object_store::Result<GetResult> {
+            let bytes = self.bytes_to_repeat.clone();
+            let arc = self.iterations_detected.clone();
+            Ok(GetResult::Stream(
+                futures::stream::repeat_with(move || {
+                    let arc_inner = arc.clone();
+                    *arc_inner.lock().unwrap() += 1;
+                    Ok(bytes.clone())
+                })
+                .take(self.max_iterations)
+                .boxed(),
+            ))
+        }
+
+        async fn get_range(
+            &self,
+            _location: &Path,
+            _range: Range<usize>,
+        ) -> object_store::Result<Bytes> {
+            unimplemented!()
+        }
+
+        async fn get_ranges(
+            &self,
+            _location: &Path,
+            _ranges: &[Range<usize>],
+        ) -> object_store::Result<Vec<Bytes>> {
+            unimplemented!()
+        }
+
+        async fn head(&self, _location: &Path) -> object_store::Result<ObjectMeta> {
+            unimplemented!()
+        }
+
+        async fn delete(&self, _location: &Path) -> object_store::Result<()> {
+            unimplemented!()
+        }
+
+        async fn list(
+            &self,
+            _prefix: Option<&Path>,
+        ) -> object_store::Result<BoxStream<'_, object_store::Result<ObjectMeta>>>
+        {
+            unimplemented!()
+        }
+
+        async fn list_with_delimiter(
+            &self,
+            _prefix: Option<&Path>,
+        ) -> object_store::Result<ListResult> {
+            unimplemented!()
+        }
+
+        async fn copy(&self, _from: &Path, _to: &Path) -> object_store::Result<()> {
+            unimplemented!()
+        }
+
+        async fn copy_if_not_exists(
+            &self,
+            _from: &Path,
+            _to: &Path,
+        ) -> object_store::Result<()> {
+            unimplemented!()
+        }
+    }
+
+    impl VariableStream {
+        pub fn new(bytes_to_repeat: Bytes, max_iterations: usize) -> Self {
+            Self {
+                bytes_to_repeat,
+                max_iterations,
+                iterations_detected: Arc::new(Mutex::new(0)),
+            }
+        }
+
+        pub fn get_iterations_detected(&self) -> usize {
+            *self.iterations_detected.lock().unwrap()
+        }
+    }
 }

datafusion/core/src/physical_plan/file_format/mod.rs

@@ -28,6 +28,7 @@ mod parquet;
 
 pub(crate) use self::csv::plan_to_csv;
 pub use self::csv::CsvExec;
+pub(crate) use self::delimited_stream::newline_delimited_stream;
 pub(crate) use self::parquet::plan_to_parquet;
 pub use self::parquet::{ParquetExec, ParquetFileMetrics, ParquetFileReaderFactory};
 use arrow::{