Server Configuration Parameters

There are many LightDB-A server configuration parameters that affect the behavior of the LightDB-A 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 describes the parameter data types and values.
• Setting Parameters describes limitations on who can change them and where or when they can be set.
• Parameter Categories organizes parameters by functionality.
• Configuration Parameters lists the parameter descriptions in alphabetic order.

Parameter Types and Values

All parameter names are case-insensitive. Every parameter takes a value of one of the following types: Boolean, integer, floating point, enum, or string.

Boolean values may be specified as ON, OFF, TRUE, FALSE, YES, NO, 1, 0 (all case-insensitive).

Enum-type parameters are specified in the same manner as string parameters, but are restricted to a limited set of values. Enum parameter values are 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 LightDB-A 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), at the database- and role-level (ALTER ROLE...IN DATABASE...SET, or at the session-level (using SET). System parameters can only be set in the postgresql.conf file.

In LightDB-A Database, the coordinator 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 (coordinator and segments). Others parameters are considered coordinator parameters. Coordinator parameters need only be set at the coordinator instance.

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