Configuring GUC Parameters

Parameter Types and Values

• The GUC parameters of GaussDB(DWS) are classified into the following types:
  • SUSET: database administrator parameters. This type of parameters take effect immediately after they are set. You do not need to restart the cluster. If a parameter of this type is set in the current session, the parameter takes effect only in the current session.
  • USERSET: common user parameters. This type of parameters take effect immediately after they are set. You do not need to restart the cluster. If a parameter of this type is set in the current session, the parameter takes effect only in the current session.
  • POSTMASTER: database server parameters. This type of parameters take effect only after the cluster is restarted. After you modify a parameter of this type, the system displays a message indicating that the cluster is to be restarted. You are advised to manually restart the cluster during off-peak hours for the setting to take effect.
  • SIGHUP: global database parameters. This type of parameters take effect globally and cannot take effect for single sessions.
  • BACKEND: global database parameters. This type of parameters take effect globally and cannot take effect for single sessions.
• All parameter names are case insensitive. A parameter value can be an integer, floating point number, string, Boolean value, or enumerated value.
  • The Boolean values can be on/off, true/false, yes/no, or 1/0, and are case-insensitive.
  • The enumerated value range is specified in the enumvals column of the system catalog pg_settings.
• For parameters using units, specify their units during the setting, or default units are used.
  • The default units are specified in the unit column of pg_settings.
  • The unit of memory can be KB, MB, or GB.
  • The unit of time can be ms, s, min, h, or d.

Setting GUC Parameters

You can configure GUC parameters in the following ways:

• Method 1: After a cluster is created, you can log in to the GaussDB(DWS) management console and modify the database parameters of the cluster. For details, see "Modifying Database Parameters" in Data Warehouse Service (DWS) User Guide.
• Method 2: Connect to a cluster and run SQL commands to configure the parameters of the SUSET or USERSET type.

  Configure parameters at database, user, or session levels.

  • Set a database-level parameter.

    1	ALTER DATABASE dbname SET paraname TO value;

    The setting takes effect in the next session.

  • Set a user-level parameter.

    1	ALTER USER username SET paraname TO value;

    The setting takes effect in the next session.

  • Set a session-level parameter.

    1	SET paraname TO value;

    Parameter value in the current session is changed. After you exit the session, the setting becomes invalid.

Procedure

The following example shows how to set explain_perf_mode.

1. View the value of explain_perf_mode.

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   SHOW explain_perf_mode; explain_perf_mode ------------------- normal (1 row)

2. Set explain_perf_mode.

   Perform one of the following operations:

   • Set a database-level parameter.

     1	ALTER DATABASE gaussdb SET explain_perf_mode TO pretty;

     If the following information is displayed, the setting has been modified.

     ALTER DATABASE

     The setting takes effect in the next session.

   • Set a user-level parameter.

     1	ALTER USER dbadmin SET explain_perf_mode TO pretty;

     If the following information is displayed, the setting has been modified.

     ALTER USER

     The setting takes effect in the next session.

   • Set a session-level parameter.

     1	SET explain_perf_mode TO pretty;

     If the following information is displayed, the setting has been modified.

     SET

3. Check whether the parameter is correctly set.

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   SHOW explain_perf_mode; explain_perf_mode -------------- pretty (1 row)