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# Supported Spark Data Sources

## File Formats

### Parquet

When `spark.comet.scan.enabled` is enabled, Parquet scans will be performed natively by Comet if all data types
in the schema are supported. When this option is not enabled, the scan will fall back to Spark. In this case,
enabling `spark.comet.convert.parquet.enabled` will immediately convert the data into Arrow format, allowing native
execution to happen after that, but the process may not be efficient.

### Apache Iceberg

Comet accelerates Iceberg scans of Parquet files. See the [Iceberg Guide] for more information.

[Iceberg Guide]: iceberg.md

### CSV

Comet provides experimental native CSV scan support. When `spark.comet.scan.csv.v2.enabled` is enabled, CSV files
are read natively for improved performance. This feature is experimental and performance benefits are
workload-dependent.

Alternatively, when `spark.comet.convert.csv.enabled` is enabled, data from Spark's CSV reader is immediately
converted into Arrow format, allowing native execution to happen after that.

### JSON

Comet does not provide native JSON scan, but when `spark.comet.convert.json.enabled` is enabled, data is immediately
converted into Arrow format, allowing native execution to happen after that.

## Data Catalogs

### Apache Iceberg

See the dedicated [Comet and Iceberg Guide](iceberg.md).

## Supported Storages

Comet supports most standard storage systems, such as local file system and object storage.

### HDFS

Apache DataFusion Comet native reader seamlessly scans files from remote HDFS for [supported formats](#supported-spark-data-sources)

### Using experimental native DataFusion reader

Unlike to native Comet reader the Datafusion reader fully supports nested types processing. This reader is currently experimental only

To build Comet with native DataFusion reader and remote HDFS support it is required to have a JDK installed

Example:
Build a Comet for `spark-3.5` provide a JDK path in `JAVA_HOME`
Provide the JRE linker path in `RUSTFLAGS`, the path can vary depending on the system. Typically JRE linker is a part of installed JDK

```shell
export JAVA_HOME="/opt/homebrew/opt/openjdk@11"
make release PROFILES="-Pspark-3.5" COMET_FEATURES=hdfs RUSTFLAGS="-L $JAVA_HOME/libexec/openjdk.jdk/Contents/Home/lib/server"
```

Start Comet with experimental reader and HDFS support as [described](installation.md/#run-spark-shell-with-comet-enabled)
and add additional parameters

```shell
--conf spark.comet.scan.impl=native_datafusion \
--conf spark.hadoop.fs.defaultFS="hdfs://namenode:9000" \
--conf spark.hadoop.dfs.client.use.datanode.hostname = true \
--conf dfs.client.use.datanode.hostname = true
```

Query a struct type from Remote HDFS

```shell
spark.read.parquet("hdfs://namenode:9000/user/data").show(false)

root
 |-- id: integer (nullable = true)
 |-- first_name: string (nullable = true)
 |-- personal_info: struct (nullable = true)
 |    |-- firstName: string (nullable = true)
 |    |-- lastName: string (nullable = true)
 |    |-- ageInYears: integer (nullable = true)

25/01/30 16:50:43 INFO core/src/lib.rs: Comet native library version $COMET_VERSION initialized
== Physical Plan ==
* CometColumnarToRow (2)
+- CometNativeScan:  (1)


(1) CometNativeScan:
Output [3]: [id#0, first_name#1, personal_info#4]
Arguments: [id#0, first_name#1, personal_info#4]

(2) CometColumnarToRow [codegen id : 1]
Input [3]: [id#0, first_name#1, personal_info#4]


25/01/30 16:50:44 INFO fs-hdfs-0.1.12/src/hdfs.rs: Connecting to Namenode (hdfs://namenode:9000)
+---+----------+-----------------+
|id |first_name|personal_info    |
+---+----------+-----------------+
|2  |Jane      |{Jane, Smith, 34}|
|1  |John      |{John, Doe, 28}  |
+---+----------+-----------------+



```

Verify the native scan type should be `CometNativeScan`.

More on [HDFS Reader](https://github.com/apache/datafusion-comet/blob/main/native/hdfs/README.md)

### Local HDFS development

- Configure local machine network. Add hostname to `/etc/hosts`

```shell
127.0.0.1	localhost   namenode datanode1 datanode2 datanode3
::1             localhost namenode datanode1 datanode2 datanode3
```

- Start local HDFS cluster, 3 datanodes, namenode url is `namenode:9000`

```shell
docker compose -f kube/local/hdfs-docker-compose.yml up
```

- Check the local namenode is up and running on `http://localhost:9870/dfshealth.html#tab-overview`
- Build a project with HDFS support

```shell
JAVA_HOME="/opt/homebrew/opt/openjdk@11" make release PROFILES="-Pspark-3.5" COMET_FEATURES=hdfs RUSTFLAGS="-L /opt/homebrew/opt/openjdk@11/libexec/openjdk.jdk/Contents/Home/lib/server"
```

- Run local test

```scala

    withSQLConf(
      CometConf.COMET_ENABLED.key -> "true",
      CometConf.COMET_EXEC_ENABLED.key -> "true",
      CometConf.COMET_NATIVE_SCAN_IMPL.key -> CometConf.SCAN_NATIVE_DATAFUSION,
      SQLConf.USE_V1_SOURCE_LIST.key -> "parquet",
      "fs.defaultFS" -> "hdfs://namenode:9000",
      "dfs.client.use.datanode.hostname" -> "true") {
      val df = spark.read.parquet("/tmp/2")
      df.show(false)
      df.explain("extended")
    }
  }
```

Or use `spark-shell` with HDFS support as described [above](#using-experimental-native-datafusion-reader)

## S3

#### Root CA Certificates

One major difference between Spark and Comet is the mechanism for discovering Root
CA Certificates. Spark uses the JVM to read CA Certificates from the Java Trust Store, but native Comet
scans use system Root CA Certificates (typically stored
in `/etc/ssl/certs` on Linux). These scans will not be able to interact with S3 if the Root CA Certificates are not
installed.

#### Supported Credential Providers

AWS credential providers can be configured using the `fs.s3a.aws.credentials.provider` configuration. The following table shows the supported credential providers and their configuration options:

| Credential provider                                                                                                                                                                          | Description                                                                                                     | Supported Options                                                                                                               |
| -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------- |
| `org.apache.hadoop.fs.s3a.SimpleAWSCredentialsProvider`                                                                                                                                      | Access S3 using access key and secret key                                                                       | `fs.s3a.access.key`, `fs.s3a.secret.key`                                                                                        |
| `org.apache.hadoop.fs.s3a.TemporaryAWSCredentialsProvider`                                                                                                                                   | Access S3 using temporary credentials                                                                           | `fs.s3a.access.key`, `fs.s3a.secret.key`, `fs.s3a.session.token`                                                                |
| `org.apache.hadoop.fs.s3a.auth.AssumedRoleCredentialProvider`                                                                                                                                | Access S3 using AWS STS assume role                                                                             | `fs.s3a.assumed.role.arn`, `fs.s3a.assumed.role.session.name` (optional), `fs.s3a.assumed.role.credentials.provider` (optional) |
| `org.apache.hadoop.fs.s3a.auth.IAMInstanceCredentialsProvider`                                                                                                                               | Access S3 using EC2 instance profile or ECS task credentials (tries ECS first, then IMDS)                       | None (auto-detected)                                                                                                            |
| `org.apache.hadoop.fs.s3a.AnonymousAWSCredentialsProvider`<br/>`com.amazonaws.auth.AnonymousAWSCredentials`<br/>`software.amazon.awssdk.auth.credentials.AnonymousCredentialsProvider`       | Access S3 without authentication (public buckets only)                                                          | None                                                                                                                            |
| `com.amazonaws.auth.EnvironmentVariableCredentialsProvider`<br/>`software.amazon.awssdk.auth.credentials.EnvironmentVariableCredentialsProvider`                                             | Load credentials from environment variables (`AWS_ACCESS_KEY_ID`, `AWS_SECRET_ACCESS_KEY`, `AWS_SESSION_TOKEN`) | None                                                                                                                            |
| `com.amazonaws.auth.InstanceProfileCredentialsProvider`<br/>`software.amazon.awssdk.auth.credentials.InstanceProfileCredentialsProvider`                                                     | Access S3 using EC2 instance metadata service (IMDS)                                                            | None                                                                                                                            |
| `com.amazonaws.auth.ContainerCredentialsProvider`<br/>`software.amazon.awssdk.auth.credentials.ContainerCredentialsProvider`<br/>`com.amazonaws.auth.EC2ContainerCredentialsProviderWrapper` | Access S3 using ECS task credentials                                                                            | None                                                                                                                            |
| `com.amazonaws.auth.WebIdentityTokenCredentialsProvider`<br/>`software.amazon.awssdk.auth.credentials.WebIdentityTokenFileCredentialsProvider`                                               | Authenticate using web identity token file                                                                      | None                                                                                                                            |

Multiple credential providers can be specified in a comma-separated list using the `fs.s3a.aws.credentials.provider` configuration, just as Hadoop AWS supports. If `fs.s3a.aws.credentials.provider` is not configured, Hadoop S3A's default credential provider chain will be used. All configuration options also support bucket-specific overrides using the pattern `fs.s3a.bucket.{bucket-name}.{option}`.
