About PXF Filter Pushdown
PXF supports filter pushdown. When filter pushdown is enabled, the constraints from the
WHERE clause of a
SELECT query can be extracted and passed to the external data source for filtering. This process can improve query performance, and can also reduce the amount of data that is transferred to Greenplum Database.
You enable or disable filter pushdown for all external table protocols, including
pxf, by setting the
gp_external_enable_filter_pushdown server configuration parameter. The default value of this configuration parameter is
on; set it to
off to disable filter pushdown. For example:
SHOW gp_external_enable_filter_pushdown; SET gp_external_enable_filter_pushdown TO 'on';
Note: Some external data sources do not support filter pushdown. Also, filter pushdown may not be supported with certain data types or operators. If a query accesses a data source that does not support filter push-down for the query constraints, the query is instead executed without filter pushdown (the data is filtered after it is transferred to Greenplum Database).
PXF accesses data sources using different connectors, and filter pushdown support is determined by the specific connector implementation. The following PXF connectors support filter pushdown:
- Hive Connector
- HBase Connector
- JDBC Connector
PXF filter pushdown can be used with these data types:
TIMESTAMP(JDBC connector only)
PXF filter pushdown can be used with these operators:
INoperator on arrays of
TEXTfields) (JDBC connector only)
To summarize, all of the following criteria must be met for filter pushdown to occur:
- You enable external table filter pushdown by setting the
gp_external_enable_filter_pushdownserver configuration parameter to
- The Greenplum Database protocol that you use to access external data source must support filter pushdown. The
pxfexternal table protocol supports pushdown.
- The external data source that you are accessing must support pushdown. For example, HBase and Hive support pushdown.
- For queries on external tables that you create with the
pxfprotocol, the underlying PXF connector must also support filter pushdown. For example, the PXF Hive, HBase, and JDBC connectors support pushdown.