Installing and Using Cloudera Impala
Cloudera Impala™ provides fast, interactive SQL queries directly on your Apache Hadoop data stored in HDFS or HBase. In addition to using the same unified storage platform, Impala also uses the same metadata, SQL syntax (Hive SQL), ODBC driver, and user interface (Hue Beeswax) as Apache Hive. This provides a familiar and unified platform for real-time or batch-oriented queries.
Cloudera Impala is an addition to tools available for querying big data. Impala does not replace the batch processing frameworks built on MapReduce such as Hive. Hive and other frameworks built on MapReduce are best suited for long running batch jobs, such as those involving batch processing of Extract, Transform, and Load (ETL) type jobs.
How Cloudera Impala Works with CDH
The Impala solution is composed of the following components:
- Clients - Entities including Hue, ODBC clients, JDBC clients, and the Impala Shell can all interact with Impala. These interfaces are typically used to issue queries or complete administrative tasks such as connecting to Impala.
- Hive Metastore - Stores information about the data available to Impala. For example, the metastore lets Impala know what databases are available and what the structure of those databases is.
- Cloudera Impala - This process, which runs on datanodes, coordinates and executes queries. Each instance of Impala can receive, plan, and coordinate queries from Impala clients. Queries are distributed among Impala nodes, and these nodes then act as workers, executing parallel query fragments.
- HBase and HDFS - Storage for data to be queried.
Queries executed using Impala are handled as follows:
- User applications send SQL queries to Impala through ODBC or JDBC, which provide standardized querying interfaces. The user application may connect to any impaladin the cluster. This impalad becomes the coordinator for the query.
- Impala parses the query and analyzes it to determine what tasks need to be performed by impaladinstances across the cluster. Execution is planned for optimal efficiency.
- Services such as HDFS and HBase are accessed by local impalad instances to provide data.
- Each impaladreturns data to the coordinating impalad, which sends these results to the client.
Primary Impala Features
Impala provides support for:
- Most common SQL-92 features of Hive Query Language (HiveQL) including SELECT, joins, and aggregate functions.
HDFS and HBase storage starting with:
- HDFS file formats: Text file, SequenceFile, RCFile, Avro file, and Parquet.
- Compression codecs: Snappy, GZIP, Deflate, BZIP.
- Common Hive interfaces including:
- Impala command-line interface.
- Kerberos authentication.
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