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new 2b7d4f9a5b feat: create a datafusion-example for in-memory file format
(#20394)
2b7d4f9a5b is described below
commit 2b7d4f9a5b005905b23128274ad37c3306ffcd15
Author: Kumar Ujjawal <[email protected]>
AuthorDate: Mon Mar 23 17:30:16 2026 +0530
feat: create a datafusion-example for in-memory file format (#20394)
## Which issue does this PR close?
<!--
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enhancements and this helps us generate change logs for our releases.
You can link an issue to this PR using the GitHub syntax. For example
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- Should close #18802 if we go this route.
## Rationale for this change
As mentioned in the original issues: there has been few questions over
in discussions about reading csv/json/parquet files from memory instead
of from disk/object store. The proposal was to add support for this or
create the example to show how to do that. I picked the latter.
<!--
Why are you proposing this change? If this is already explained clearly
in the issue then this section is not needed.
Explaining clearly why changes are proposed helps reviewers understand
your changes and offer better suggestions for fixes.
-->
## What changes are included in this PR?
- Create example for this
<!--
There is no need to duplicate the description in the issue here but it
is sometimes worth providing a summary of the individual changes in this
PR.
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## Are these changes tested?
Yes
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2. Serve as another way to document the expected behavior of the code
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## Are there any user-facing changes?
No
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---------
Co-authored-by: Jax Liu <[email protected]>
Co-authored-by: Adrian Garcia Badaracco
<[email protected]>
Co-authored-by: Martin Grigorov <[email protected]>
---
datafusion-examples/README.md | 25 +++----
.../examples/data_io/in_memory_object_store.rs | 81 ++++++++++++++++++++++
datafusion-examples/examples/data_io/main.rs | 10 ++-
3 files changed, 103 insertions(+), 13 deletions(-)
diff --git a/datafusion-examples/README.md b/datafusion-examples/README.md
index 2cf0ec5240..ebb1bc5fa6 100644
--- a/datafusion-examples/README.md
+++ b/datafusion-examples/README.md
@@ -88,18 +88,19 @@ cargo run --example dataframe -- dataframe
#### Category: Single Process
-| Subcommand | File Path
| Description
|
-| -------------------- |
-----------------------------------------------------------------------------------------
| ------------------------------------------------------ |
-| catalog | [`data_io/catalog.rs`](examples/data_io/catalog.rs)
| Register tables into a custom catalog
|
-| json_shredding |
[`data_io/json_shredding.rs`](examples/data_io/json_shredding.rs)
| Implement filter rewriting for JSON shredding |
-| parquet_adv_idx |
[`data_io/parquet_advanced_index.rs`](examples/data_io/parquet_advanced_index.rs)
| Create a secondary index across multiple parquet files |
-| parquet_emb_idx |
[`data_io/parquet_embedded_index.rs`](examples/data_io/parquet_embedded_index.rs)
| Store a custom index inside Parquet files |
-| parquet_enc |
[`data_io/parquet_encrypted.rs`](examples/data_io/parquet_encrypted.rs)
| Read & write encrypted Parquet files |
-| parquet_enc_with_kms |
[`data_io/parquet_encrypted_with_kms.rs`](examples/data_io/parquet_encrypted_with_kms.rs)
| Encrypted Parquet I/O using a KMS-backed factory |
-| parquet_exec_visitor |
[`data_io/parquet_exec_visitor.rs`](examples/data_io/parquet_exec_visitor.rs)
| Extract statistics by visiting an ExecutionPlan |
-| parquet_idx |
[`data_io/parquet_index.rs`](examples/data_io/parquet_index.rs)
| Create a secondary index |
-| query_http_csv |
[`data_io/query_http_csv.rs`](examples/data_io/query_http_csv.rs)
| Query CSV files via HTTP |
-| remote_catalog |
[`data_io/remote_catalog.rs`](examples/data_io/remote_catalog.rs)
| Interact with a remote catalog |
+| Subcommand | File Path
| Description
|
+| ---------------------- |
-----------------------------------------------------------------------------------------
| ------------------------------------------------------------------------- |
+| catalog | [`data_io/catalog.rs`](examples/data_io/catalog.rs)
| Register tables into a custom catalog
|
+| in_memory_object_store |
[`data_io/in_memory_object_store.rs`](examples/data_io/in_memory_object_store.rs)
| Read CSV from an in-memory object store (pattern applies to
JSON/Parquet) |
+| json_shredding |
[`data_io/json_shredding.rs`](examples/data_io/json_shredding.rs)
| Implement filter rewriting for JSON shredding
|
+| parquet_adv_idx |
[`data_io/parquet_advanced_index.rs`](examples/data_io/parquet_advanced_index.rs)
| Create a secondary index across multiple parquet files
|
+| parquet_emb_idx |
[`data_io/parquet_embedded_index.rs`](examples/data_io/parquet_embedded_index.rs)
| Store a custom index inside Parquet files
|
+| parquet_enc |
[`data_io/parquet_encrypted.rs`](examples/data_io/parquet_encrypted.rs)
| Read & write encrypted Parquet files
|
+| parquet_enc_with_kms |
[`data_io/parquet_encrypted_with_kms.rs`](examples/data_io/parquet_encrypted_with_kms.rs)
| Encrypted Parquet I/O using a KMS-backed factory |
+| parquet_exec_visitor |
[`data_io/parquet_exec_visitor.rs`](examples/data_io/parquet_exec_visitor.rs)
| Extract statistics by visiting an ExecutionPlan
|
+| parquet_idx |
[`data_io/parquet_index.rs`](examples/data_io/parquet_index.rs)
| Create a secondary index
|
+| query_http_csv |
[`data_io/query_http_csv.rs`](examples/data_io/query_http_csv.rs)
| Query CSV files via HTTP
|
+| remote_catalog |
[`data_io/remote_catalog.rs`](examples/data_io/remote_catalog.rs)
| Interact with a remote catalog
|
## DataFrame Examples
diff --git a/datafusion-examples/examples/data_io/in_memory_object_store.rs
b/datafusion-examples/examples/data_io/in_memory_object_store.rs
new file mode 100644
index 0000000000..9a308f06c5
--- /dev/null
+++ b/datafusion-examples/examples/data_io/in_memory_object_store.rs
@@ -0,0 +1,81 @@
+// 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.
+
+//! See `main.rs` for how to run it.
+//!
+//! This follows the recommended approach: implement the `ObjectStore` trait
+//! (or use an existing implementation), register it with DataFusion, and then
+//! read a URL "path" from that store.
+//! See the in-memory reference implementation:
+//!
https://docs.rs/object_store/latest/object_store/memory/struct.InMemory.html
+
+use std::sync::Arc;
+
+use arrow::datatypes::{DataType, Field, Schema};
+use datafusion::assert_batches_eq;
+use datafusion::common::Result;
+use datafusion::execution::object_store::ObjectStoreUrl;
+use datafusion::prelude::{CsvReadOptions, SessionContext};
+use object_store::memory::InMemory;
+use object_store::path::Path;
+use object_store::{ObjectStore, ObjectStoreExt, PutPayload};
+
+/// Demonstrates reading CSV data from an in-memory object store.
+///
+/// The same pattern applies to JSON/Parquet: register a store for a URL
+/// prefix, write bytes into the store, then read via that URL.
+pub async fn in_memory_object_store() -> Result<()> {
+ let store: Arc<dyn ObjectStore> = Arc::new(InMemory::new());
+ let ctx = SessionContext::new();
+ let object_store_url = ObjectStoreUrl::parse("memory://")?;
+ // Register a URL prefix to route reads through this object store.
+ ctx.register_object_store(object_store_url.as_ref(), Arc::clone(&store));
+
+ let schema = Schema::new(vec![
+ Field::new("id", DataType::Int64, false),
+ Field::new("name", DataType::Utf8, false),
+ ]);
+
+ println!("=== CSV from memory ===");
+ let csv_path = Path::from("/people.csv");
+ let csv_data = b"id,name\n1,Alice\n2,Bob\n";
+ // Write bytes into the in-memory object store.
+ store
+ .put(&csv_path, PutPayload::from_static(csv_data))
+ .await?;
+ // Read using the URL that matches the registered prefix.
+ let csv = ctx
+ .read_csv(
+ "memory:///people.csv",
+ CsvReadOptions::new().schema(&schema),
+ )
+ .await?
+ .collect()
+ .await?;
+ #[rustfmt::skip]
+ let expected = [
+ "+----+-------+",
+ "| id | name |",
+ "+----+-------+",
+ "| 1 | Alice |",
+ "| 2 | Bob |",
+ "+----+-------+",
+ ];
+ assert_batches_eq!(expected, &csv);
+
+ Ok(())
+}
diff --git a/datafusion-examples/examples/data_io/main.rs
b/datafusion-examples/examples/data_io/main.rs
index 0039585d15..4656a83670 100644
--- a/datafusion-examples/examples/data_io/main.rs
+++ b/datafusion-examples/examples/data_io/main.rs
@@ -21,7 +21,7 @@
//!
//! ## Usage
//! ```bash
-//! cargo run --example data_io --
[all|catalog|json_shredding|parquet_adv_idx|parquet_emb_idx|parquet_enc_with_kms|parquet_enc|parquet_exec_visitor|parquet_idx|query_http_csv|remote_catalog]
+//! cargo run --example data_io --
[all|catalog|in_memory_object_store|json_shredding|parquet_adv_idx|parquet_emb_idx|parquet_enc_with_kms|parquet_enc|parquet_exec_visitor|parquet_idx|query_http_csv|remote_catalog]
//! ```
//!
//! Each subcommand runs a corresponding example:
@@ -30,6 +30,9 @@
//! - `catalog`
//! (file: catalog.rs, desc: Register tables into a custom catalog)
//!
+//! - `in_memory_object_store`
+//! (file: in_memory_object_store.rs, desc: Read CSV from an in-memory
object store (pattern applies to JSON/Parquet))
+//!
//! - `json_shredding`
//! (file: json_shredding.rs, desc: Implement filter rewriting for JSON
shredding)
//!
@@ -58,6 +61,7 @@
//! (file: remote_catalog.rs, desc: Interact with a remote catalog)
mod catalog;
+mod in_memory_object_store;
mod json_shredding;
mod parquet_advanced_index;
mod parquet_embedded_index;
@@ -77,6 +81,7 @@ use strum_macros::{Display, EnumIter, EnumString,
VariantNames};
enum ExampleKind {
All,
Catalog,
+ InMemoryObjectStore,
JsonShredding,
ParquetAdvIdx,
ParquetEmbIdx,
@@ -104,6 +109,9 @@ impl ExampleKind {
}
}
ExampleKind::Catalog => catalog::catalog().await?,
+ ExampleKind::InMemoryObjectStore => {
+ in_memory_object_store::in_memory_object_store().await?
+ }
ExampleKind::JsonShredding =>
json_shredding::json_shredding().await?,
ExampleKind::ParquetAdvIdx => {
parquet_advanced_index::parquet_advanced_index().await?
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