Server Configuration Parameters

Server Configuration Parameters

There are many Greenplum server configuration parameters that affect the behavior of the Greenplum Database system. Many of these configuration parameters have the same names, settings, and behaviors as in a regular PostgreSQL database system.

Parameter Types and Values

All parameter names are case-insensitive. Every parameter takes a value of one of four types: Boolean, integer, floating point, or string. Boolean values may be written as ON, OFF, TRUE, FALSE, YES, NO, 1, 0 (all case-insensitive).

Some settings specify a memory size or time value. Each of these has an implicit unit, which is either kilobytes, blocks (typically eight kilobytes), milliseconds, seconds, or minutes. Valid memory size units are kB (kilobytes), MB (megabytes), and GB (gigabytes). Valid time units are ms (milliseconds), s (seconds), min (minutes), h (hours), and d (days). Note that the multiplier for memory units is 1024, not 1000. A valid time expression contains a number and a unit. When specifying a memory or time unit using the SET command, enclose the value in quotes. For example:

SET statement_mem TO '200MB';
Note: There is no space between the value and the unit names.

Setting Parameters

Many of the configuration parameters have limitations on who can change them and where or when they can be set. For example, to change certain parameters, you must be a Greenplum Database superuser. Other parameters require a restart of the system for the changes to take effect. A parameter that is classified as session can be set at the system level (in the postgresql.conf file), at the database-level (using ALTER DATABASE), at the role-level (using ALTER ROLE), or at the session-level (using SET). System parameters can only be set in the postgresql.conf file.

In Greenplum Database, the master and each segment instance has its own postgresql.conf file (located in their respective data directories). Some parameters are considered local parameters, meaning that each segment instance looks to its own postgresql.conf file to get the value of that parameter. You must set local parameters on every instance in the system (master and segments). Others parameters are considered master parameters. Master parameters need only be set at the master instance.

This table describes the values in the Settable Classifications column of the table in the description of a server configuration parameter.

Table 1. Settable Classifications
Set Classification Description
master or local A master parameter only needs to be set in the postgresql.conf file of the Greenplum master instance. The value for this parameter is then either passed to (or ignored by) the segments at run time.

A local parameter must be set in the postgresql.conf file of the master AND each segment instance. Each segment instance looks to its own configuration to get the value for the parameter. Local parameters always requires a system restart for changes to take effect.

session or system Session parameters can be changed on the fly within a database session, and can have a hierarchy of settings: at the system level (postgresql.conf), at the database level (ALTER DATABASE...SET), at the role level (ALTER ROLE...SET), or at the session level (SET). If the parameter is set at multiple levels, then the most granular setting takes precedence (for example, session overrides role, role overrides database, and database overrides system).

A system parameter can only be changed via the postgresql.conf file(s).

restart or reload When changing parameter values in the postgrsql.conf file(s), some require a restart of Greenplum Database for the change to take effect. Other parameter values can be refreshed by just reloading the server configuration file (using gpstop -u), and do not require stopping the system.
superuser These session parameters can only be set by a database superuser. Regular database users cannot set this parameter.
read only These parameters are not settable by database users or superusers. The current value of the parameter can be shown but not altered.