Fault Tolerance

This section describes parameters used for controlling the methods that the server processes an error occurring in the database system.

exit_on_error

Parameter description: Specifies whether to terminate the current session.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

Value range: Boolean

• on indicates that any error will terminate the current session.
• off indicates that only a FATAL error will terminate the current session.

Default value: off

restart_after_crash

Parameter description: Specifies whether MogDB automatically reinitializes the backend process when a backend process crashes.

This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

Value range: Boolean

• on indicates that MogDB automatically reinitializes the backend process when a backend process crashes.

  In some circumstances (for example, when a management tool, such as xCAT, is used to manage MogDB), setting this parameter to on maximizes the availability of the database.

• off indicates a management tool is enabled to obtain control permission and take proper measures when a backend process crashes.

Default value: on

omit_encoding_error

Parameter description: If this parameter is set to on and the client character set of the database is encoded in UTF-8 format, the occurring character encoding conversion errors will be recorded in logs. Additionally, converted characters that have conversion errors will be ignored and replaced with question marks (?).

This parameter is a USERSET parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

Value range: Boolean

• on indicates that characters that have conversion errors will be ignored and replaced with question marks (?), and error information will be recorded in logs.
• off indicates that characters that have conversion errors cannot be converted and error information will be directly displayed.

Default value: off

max_query_retry_times

Parameter description: Specifies the maximum number of times that an SQL statement with errors can be re-executed. SQL statements with the following types of errors can be re-executed:Connection reset by peer, Lock wait timeout, and Connection timed out. If this parameter is set to 0, the re-execution function is disabled.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

Value range: an integer ranging from 0 to 20

Default value: 0

cn_send_buffer_size

Parameter description: Specifies the size of the data buffer used for data transmission on the primary database node.

This parameter is a POSTMASTER parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

Value range: an integer ranging from 8 to 128. The unit is KB.

Default value: 8KB

max_cn_temp_file_size

Parameter description: Specifies the maximum number of temporary files that can be used by the the primary node of the database during automatic SQL statement retries. The value 0 indicates that no temporary file is used.

This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

Value range: an integer ranging from 0 to 10485760. The unit is KB.

Default value: 5GB

retry_ecode_list

Parameter description: Specifies the list of SQL error types that support automatic retry.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

Value range: a string

Default value: YY001 YY002 YY003 YY004 YY005 YY006 YY007 YY008 YY009 YY010 YY011 YY012 YY013 YY014 YY015 53200 08006 08000 57P01 XX003 XX009 YY016

data_sync_retry

Parameter description: Specifies whether to keep running the database when updated data fails to be written into disks by using the fsync function. In some OSs, no error is reported even if fsync has failed for multiple times. As a result, data is lost.

This parameter is a POSTMASTER parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

Value range: Boolean

• on: The database keeps running and fsync is executed again after fsync fails.
• off:PANIC is reported and the database is stopped after fsync fails.

Default value: off