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  3. Developer Guide
  4. Setting Configuration Parameters
  5. Appendix B: GUC Parameter Description
  6. Cluster Transaction Parameters

Cluster Transaction Parameters

This section describes the settings and value ranges of cluster transaction parameters.

transaction_isolation

Parameter description: Specifies the isolation level of the current transaction.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

The options are as follows:

  • serializable: equal to read committed in DWS.
  • read committed: by default, reads the transaction data only after the transaction is submitted.
  • repeatable read: equal to read committed in DWS.
  • read uncommitted: may read the transaction data before the transaction is submitted. This parameter value may result in data inconsistencies and therefore is not recommended. It can be used if CN faults cannot be rectified in a timely manner, thereby avoiding inconsistencies between the GTM and CN/DN. This parameter value can also be used for emergent read transactions. However, this parameter value is not recommended for write transactions. If this parameter value is used for write transactions, data inconsistencies may occur.

Default value: read committed

transaction_read_only

Parameter description: specifies that the current transaction is a read-only transaction.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on indicates that the current transaction is a read-only transaction.
  • off indicates that the current transaction can be a read/write transaction.

Default value: off

xc_maintenance_mode

Parameter description: specifies whether the system is in maintenance mode.

This parameter is a SUSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on indicates that concurrent update is allowed.
  • off indicates that concurrent update is disallowed.

Enable the maintenance mode with caution to avoid cluster data inconsistencies.

Default value: off

allow_concurrent_tuple_update

Parameter description: Specifies whether to allow concurrent update.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on indicates that concurrent update is allowed.
  • off indicates that concurrent update is disallowed.

Default value: on

gtm_backup_barrier

Parameter description: specifies whether to create a restoration point for the GTM starting point.

This parameter is a SUSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on indicates that a restoration point will be created for the GTM starting point.
  • off indicates that a restoration point will not be created for the GTM starting point.

Default value: off

transaction_deferrable

Parameter description: specifies whether to delay the execution of a read-only serial transaction without incurring an execution failure. Assume this parameter is set to on. When the server detects that the tuples read by a read-only transaction are being modified by other transactions, it delays the execution of the read-only transaction until the other transactions finish modifying the tuples. Currently, this parameter is not used in DWS. The default_transaction_deferrable parameter similar to this parameter is used to specify whether to allow delayed execution of a transaction.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on indicates that the execution of a read-only serial transaction can be delayed.
  • off indicates that the execution of a read-only serial transaction cannot be delayed.

Default value: off

enforce_two_phase_commit

Parameter description: This parameter has been discarded in DWS.

enable_show_any_tuples

Parameter description: This parameter is available only in a read-only transaction and is used for analysis. When this parameter is set to on/true, all versions of tuples in the table are displayed.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on/true indicates that all versions of tuples in the table are displayed.
  • off/false indicates that no versions of tuples in the table are displayed.

Default value: off

enable_redistribute

Parameter description: Whether unmatched nodes are redistributed.

This parameter is a SUSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on indicates that unmatched nodes are redistributed.
  • off indicates that unmatched nodes are not redistributed.

Default value: off