Cluster Transaction Parameters

transaction_isolation

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

Type: USERSET

Value range:

• READ COMMITTED: Only committed data is read. This is the default.
• READ UNCOMMITTED: GaussDB(DWS) does not support READ UNCOMMITTED. If READ UNCOMMITTED is set, READ COMMITTED is executed instead.
• REPEATABLE READ: Only the data committed before transaction start is read. Uncommitted data or data committed in other concurrent transactions cannot be read.
• SERIALIZABLE: GaussDB(DWS) does not support SERIALIZABLE. If SERIALIZABLE is set, REPEATABLE READ is executed instead.

Default value: READ COMMITTED

transaction_read_only

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

Type: USERSET

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 for CNs and on for DNs

xc_maintenance_mode

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

Type: SUSET

Value range: Boolean

• on indicates that maintenance mode is enabled.
• off indicates that the maintenance mode is disabled.

Default value: off

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

allow_concurrent_tuple_update

Parameter description: Specifies whether to allow concurrent update.

Type: USERSET

Value range: Boolean

• on indicates it is enabled.
• off indicates it is disabled.

Default value: on

gtm_backup_barrier

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

Type: SUSET

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

gtm_conn_check_interval

Parameter description: Sets the CN to check whether the connection between the local thread and the primary GTM is normal.

Type: SUSET

Value range: an integer ranging from 0 to INT_MAX/1000. The unit is second.

Default value: 10s

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 GaussDB(DWS). Similar to this parameter, the default_transaction_deferrable parameter is used to specify whether to allow delayed execution of a transaction.

Type: USERSET

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 is reserved for compatibility with earlier versions. This parameter is invalid in the current version.

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.

Type: USERSET

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

gtm_connect_retries

Parameter description: Specifies the number of GTM reconnection attempts.

Type: SIGHUP

Value range: an integer ranging from 1 to 2147483647.

Default value: 30

enable_redistribute

Parameter description: Specifies whether unmatched nodes are redistributed.

Type: SUSET

Value range: Boolean

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

Default value: off

enable_gtm_free

Parameter description: Specifies whether the GTM-FREE mode is enabled. In large concurrency scenarios, the snapshots delivered by the GTM increase in number and size. The network between the GTM and the CN becomes the performance bottleneck. The GTM-FREE mode is used to eliminate the bottleneck. In this mode, the CN communicates with DNs instead of the GTM. The CN sends queries to each DN, which locally generates snapshots and xids, ensuring external write consistency but not external read consistency.

You are not advised to set this parameter to on in OLTP or OLAP scenarios where strong read consistency is required. This parameter is invalid for GaussDB(DWS).

Type: SUSET

Value range: Boolean

• on indicates that the GTM-FREE mode is enabled and the cluster ensures eventual read consistency.
• off indicates that the GTM-FREE mode is disabled.

Default value: off