A distributed file system that provides high-throughput access to application data.

Capabilities

This service can be used to:

• [x] stat
• [x] read
• [x] write
• [x] create_dir
• [x] delete
• [ ] copy
• [ ] rename
• [x] list
• [ ] scan
• [ ] presign
• [x] blocking

Differences with webhdfs

[Webhdfs][crate::services::Webhdfs] is powered by hdfs's RESTful HTTP API.

Features

HDFS support needs to enable feature services-hdfs.

Configuration

• root: Set the work dir for backend.
• name_node: Set the name node for backend.

Refer to [HdfsBuilder]'s public API docs for more information.

Environment

HDFS needs some environment set correctly.

• JAVA_HOME: the path to java home, could be found via java -XshowSettings:properties -version
• HADOOP_HOME: the path to hadoop home, opendal relays on this env to discover hadoop jars and set CLASSPATH automatically.

Most of the time, setting JAVA_HOME and HADOOP_HOME is enough. But there are some edge cases:

• If meeting errors like the following:

error while loading shared libraries: libjvm.so: cannot open shared object file: No such file or directory

Java's lib are not including in pkg-config find path, please set LD_LIBRARY_PATH:

export LD_LIBRARY_PATH=${JAVA_HOME}/lib/server:${LD_LIBRARY_PATH}

The path of libjvm.so could be different, please keep an eye on it.

• If meeting errors like the following:

(unable to get stack trace for java.lang.NoClassDefFoundError exception: ExceptionUtils::getStackTrace error.)

CLASSPATH is not set correctly or your hadoop installation is incorrect.

To set CLASSPATH:

export CLASSPATH=$(find $HADOOP_HOME -iname "*.jar" | xargs echo | tr ' ' ':'):${CLASSPATH}

Example

Via Builder

use std::sync::Arc;

use anyhow::Result;
use opendal::services::Hdfs;
use opendal::Operator;

#[tokio::main]
async fn main() -> Result<()> {
    // Create fs backend builder.
    let mut builder = Hdfs::default();
    // Set the name node for hdfs.
    builder.name_node("hdfs://127.0.0.1:9000");
    // Set the root for hdfs, all operations will happen under this root.
    //
    // NOTE: the root must be absolute path.
    builder.root("/tmp");

    // `Accessor` provides the low level APIs, we will use `Operator` normally.
    let op: Operator = Operator::new(builder)?.finish();

    Ok(())
}