Reading and Writing ORC Data in an Object Store

The PXF object store connectors support reading and writing ORC-formatted data. This section describes how to use PXF to access ORC data in an object store, including how to create and query an external table that references a file in the store.

Note: Accessing ORC-formatted data from an object store is very similar to accessing ORC-formatted data in HDFS. This topic identifies object store-specific information required to read and write ORC data, and links to the PXF Hadoop ORC documentation where appropriate for common information.

Prerequisites

Ensure that you have met the PXF Object Store Prerequisites before you attempt to read data from or write data to an object store.

Data Type Mapping

Refer to Data Type Mapping in the PXF Hadoop ORC documentation for a description of the mapping between Greenplum Database and ORC data types.

Creating the External Table

The PXF <objstore>:orc profiles support reading and writing data in ORC format. PXF supports the following <objstore> profile prefixes:

Object Store	Profile Prefix
Azure Blob Storage	wasbs
Azure Data Lake	adl
Google Cloud Storage	gs
MinIO	s3
S3	s3

Use the following syntax to create a Greenplum Database external table that references an object store file. When you insert records into a writable external table, the block(s) of data that you insert are written to one or more files in the directory that you specified.

CREATE [WRITABLE] EXTERNAL TABLE <table_name>
    ( <column_name> <data_type> [, ...] | LIKE <other_table> )
LOCATION ('pxf://<path-to-file>?PROFILE=<objstore>:orc&SERVER=<server_name>[&<custom-option>=<value>[...]]')
FORMAT 'CUSTOM' (FORMATTER='pxfwritable_import'|'pxfwritable_export')
[DISTRIBUTED BY (<column_name> [, ... ] ) | DISTRIBUTED RANDOMLY];

The specific keywords and values used in the Greenplum Database CREATE EXTERNAL TABLE command are described in the table below.

Keyword	Value
<path‑to‑file>	The path to the directory or file in the object store. When the <server_name> configuration includes a pxf.fs.basePath property setting, PXF considers <path‑to‑file> to be relative to the base path specified. Otherwise, PXF considers it to be an absolute path. <path‑to‑file> must not specify a relative path nor include the dollar sign ($) character.
PROFILE=<objstore>:orc	The PROFILE keyword must identify the specific object store. For example, s3:orc.
SERVER=<server_name>	The named server configuration that PXF uses to access the data.
<custom‑option>=<value>	ORC supports customs options as described in the PXF Hadoop ORC documentation.
FORMAT ‘CUSTOM’	Use FORMAT ‘CUSTOM’ with (FORMATTER='pxfwritable_export') (write) or (FORMATTER='pxfwritable_import') (read).
DISTRIBUTED BY	If you want to load data from an existing Greenplum Database table into the writable external table, consider specifying the same distribution policy or <column_name> on both tables. Doing so will avoid extra motion of data between segments on the load operation.

If you are accessing an S3 object store, you can provide S3 credentials via custom options in the CREATE EXTERNAL TABLE command as described in Overriding the S3 Server Configuration with DDL.

Example

Refer to Example: Reading an ORC File on HDFS in the PXF Hadoop ORC documentation for an example. Modifications that you must make to run the example with an object store include:

• Copying the ORC file to the object store instead of HDFS. For example, to copy the file to S3:

  $ aws s3 cp /tmp/sampledata.orc s3://BUCKET/pxf_examples/orc_example/
  

• Using the CREATE EXTERNAL TABLE syntax and LOCATION keywords and settings described above. For example, if your server name is s3srvcfg:

  CREATE EXTERNAL TABLE sample_orc( location TEXT, month TEXT, num_orders INTEGER, total_sales NUMERIC(10,2), items_sold TEXT[] )
    LOCATION('pxf://BUCKET/pxf_examples/orc_example?PROFILE=s3:orc&SERVER=s3srvcfg')
  FORMAT 'CUSTOM' (FORMATTER='pxfwritable_import');
  

• Using the CREATE WRITABLE EXTERNAL TABLE syntax and LOCATION keywords and settings described above for the writable external table. For example, if your server name is s3srvcfg:

  CREATE WRITABLE EXTERNAL TABLE write_to_sample_orc (location TEXT, month TEXT, num_orders INT, total_sales NUMERIC(10,2), items_sold TEXT[])
    LOCATION ('pxf://BUCKET/pxf_examples/orc_example?PROFILE=s3:orc&SERVER=s3srvcfg')
  FORMAT 'CUSTOM' (FORMATTER='pxfwritable_export');