Working with HDFS¶

This is a simple guide that demonstrates how to use TileDB on HDFS. HDFS is a distributed Java-based filesystem for storing large amounts of data. It is the underlying distributed storage layer for the Hadoop stack.

Note

The HDFS backend currently only works on POSIX (Linux, OSX) platforms. Windows is currently not supported.

TileDB integrates with HDFS through the libhdfs library (HDFS C-API). The HDFS backend is enabled by default and libhdfs loading happens at runtime based on environment variables:

HDFS environment variables¶
Environment variable	Description
`HADOOP_HOME`	The root of your installed Hadoop distribution. TileDB will search the path `$HADOOP_HOME/lib/native` to find the `libhdfs` shared library.
`JAVA_HOME`	The location of the Java SDK installation. The `JAVA_HOME` variable may be set to the root path for the JAVA SDK, the JRE path, or to the directory containing the `libjvm` library.
`CLASSPATH`	The Java classpath including the Hadoop jar files. The correct `CLASSPATH` variable can be set directly using the hadoop utility: `CLASSPATH=$HADOOP_HOME/bin/hadoop classpath –glob`

If the library cannot be found, or if the Hadoop library cannot locate the correct library dependencies a runtime, an error will be returned.

To use HDFS with TileDB, change the URI you use to an HDFS path:

hdfs://<authority>:<port>/path/to/array

For instance, if you are running a local HDFS namenode on port 9000:

hdfs://localhost:9000/path/to/array

If you want to use the namenode specified in your HDFS configuration files, then change the prefix to:

hdfs:///path/to/array or hdfs://default/path/to/array

Most HDFS configuration variables are defined in Hadoop specific XML files. TileDB allows the following configuration variables to be set at run time through configuration parameters:

TileDB HDFS config parameters¶
Parameter	Description
`vfs.hdfs.username`	Optional runtime username to use when connecting to the HDFS cluster.
`vfs.hdfs.name_node_uri`	Optional namenode URI to use (TileDB will use `"default"` if not specified). URI must be specified in the format `<protocol>://<hostname>:<port>`, ex: `hdfs://localhost:9000`. If the string starts with a protocol type such as `file://` or `s3://`, this protocol will be used instead of the default `hdfs://`.
`vfs.hdfs.kerb_ticket_cache_path`	Path to the Kerberos ticket cache when connecting to an HDFS cluster.