ClickHouse/docs/en/operations/table_engines/hdfs.md

HDFS

This engine provides integration with Apache Hadoop ecosystem by allowing to manage data on HDFSvia ClickHouse. This engine is similar to the File and URL engines, but provides Hadoop-specific features.

Usage

ENGINE = HDFS(URI, format)

The format parameter specifies one of the available file formats. To perform SELECT queries, the format must be supported for input, and to perform INSERT queries -- for output. The available formats are listed in the Formats section.

Example:

1. Set up the HDFS_engine_table table:

CREATE TABLE hdfs_engine_table (name String, value UInt32) ENGINE=HDFS('hdfs://hdfs1:9000/other_storage', 'TSV')

2. Query the data:

SELECT * FROM hdfs_engine_table LIMIT 2

┌─name─┬─value─┐
│ one  │     1 │
│ two  │     2 │
└──────┴───────┘

Details of Implementation

• Reads and writes can be parallel
• Not supported:
  • ALTER and SELECT...SAMPLE operations.
  • Indexes.
  • Replication.

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