hive - Multiple Spark applications with HiveContext

Question

Having two separate pyspark applications that instantiate a HiveContext in place of a SQLContext lets one of the two applications fail with the error:

Exception: ("You must build Spark with Hive. Export 'SPARK_HIVE=true' and run build/sbt assembly", Py4JJavaError(u'An error occurred while calling None.org.apache.spark.sql.hive.HiveContext. ', JavaObject id=o34039))

The other application terminates successfully.

I am using Spark 1.6 from the Python API and want to make use of some Dataframe functions, that are only supported with a HiveContext (e.g. collect_set). I've had the same issue on 1.5.2 and earlier.

This is enough to reproduce:

import time
from pyspark import SparkContext, SparkConf
from pyspark.sql import SQLContext

conf = SparkConf()
sc = SparkContext(conf=conf)
sq = HiveContext(sc)

data_source = '/tmp/data.parquet'
df = sq.read.parquet(data_source)
time.sleep(60)

The sleep is just to keep the script running while I start the other process.

If I have two instances of this script running, the above error shows when reading the parquet-file. When I replace HiveContext with SQLContext everything's fine.

Does anyone know why that is?

Answer 1

By default Hive(Context) is using embedded Derby as a metastore. It is intended mostly for testing and supports only one active user. If you want to support multiple running applications you should configure a standalone metastore. At this moment Hive supports PostgreSQL, MySQL, Oracle and MySQL. Details of configuration depend on a backend and option (local / remote) but generally speaking you'll need:

• a running RDBMS server
• a metastore database created using provided scripts
• a proper Hive configuration

Cloudera provides a comprehensive guide you may find useful: Configuring the Hive Metastore.

Theoretically it should be also possible to create separate Derby metastores with a proper configuration (see Hive Admin Manual - Local/Embedded Metastore Database) or to use Derby in Server Mode.

For development you can start applications in different working directories. This will create separate metastore_db for each application and avoid the issue of multiple active users. Providing separate Hive configuration should work as well but is less useful in development:

When not configured by the hive-site.xml, the context automatically creates metastore_db in the current directory