[GitHub] [arrow] alamb commented on a change in pull request #8731: [Rust] [RFC] Native Rust Arrow SQL IO

[GitBox <gi...@apache.org>]

alamb commented on a change in pull request #8731:
URL: https://github.com/apache/arrow/pull/8731#discussion_r532030344



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File path: rust/datafusion/src/physical_plan/sql.rs
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@@ -0,0 +1,246 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//! Execution plan for reading Parquet files
+
+use std::any::Any;
+use std::sync::Arc;
+use std::task::{Context, Poll};
+use std::{fmt, thread};
+
+use super::{RecordBatchStream, SendableRecordBatchStream};
+use crate::error::{DataFusionError, Result};
+use crate::physical_plan::ExecutionPlan;
+use crate::physical_plan::Partitioning;
+use arrow::datatypes::SchemaRef;
+use arrow::error::{ArrowError, Result as ArrowResult};
+use arrow::record_batch::RecordBatch;
+use arrow_sql::postgres::PostgresReadIterator;
+use crossbeam::channel::{bounded, Receiver, RecvError, Sender};
+use fmt::Debug;
+
+use async_trait::async_trait;
+use futures::stream::Stream;
+
+/// Execution plan for scanning a SQL data source
+#[derive(Debug, Clone)]
+pub struct SqlExec {
+    /// SQL connection
+    connection: String,
+    /// SQL query
+    query: String,
+    /// Schema after projection is applied
+    schema: SchemaRef,
+    /// Projection for which columns to load
+    projection: Vec<usize>,
+    /// Batch size
+    batch_size: usize,
+}
+
+impl SqlExec {
+    /// Create a new SQL reader execution plan
+    pub fn try_new(
+        connection: &str,
+        query: &str,
+        projection: Option<Vec<usize>>,
+        batch_size: usize,
+    ) -> Result<Self> {
+        // TODO: we could/should determine the type of database at this point

Review comment:
       I think @andygrove 's suggestion of using some generic database connectivity layer here (e.g. RDBC https://github.com/tokio-rs/rdbc) rather than building our own registry / set of database drivers would be a good idea to avoid duplicating the (substantial) effort needed for various database connectivity. 

##########
File path: rust/sql/src/lib.rs
##########
@@ -0,0 +1,79 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#![allow(dead_code)]
+
+use arrow::datatypes::{Schema, SchemaRef};
+use arrow::error::Result;
+use arrow::record_batch::RecordBatch;
+
+// supported database modules
+pub mod postgres;
+
+///
+/// a SQL data source, used to read data from a SQL database into Arrow batches
+pub trait SqlDataSource {

Review comment:
       This code seems similar to https://github.com/tokio-rs/rdbc (e.g. `Connection`, `Driver` and `ResultSet`)

##########
File path: rust/sql/src/postgres/reader.rs
##########
@@ -0,0 +1,938 @@
+// Licensed to the Apache Software Foundation (ASF) under one

Review comment:
       This is pretty cool (a partial implementation of hte postgres line protocol and conversions to/from arrow). I wonder if we could leverage something like https://github.com/sfackler/rust-postgres rather than taking on a new independent implementation




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