MogDB Transaction

This section describes the settings and value ranges of MogDB 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 GUC parameters.

Value range: a string of case-sensitive characters. The values include:

• serializable: This value is equivalent to REPEATABLE READ in MogDB.
• read committed: Only the data in committed transactions will be read.
• repeatable read: Only the data committed before transaction start is read. Uncommitted data or data committed in other concurrent transactions cannot be read.
• default: The value is the same as that of default_transaction_isolation.

Default value: read committed

transaction_read_only

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

This parameter is fixed to on during the database recovery process or in the standby machine; otherwise, it is fixed to the value of default_transaction_read_only.

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

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 method 3 in Table 1 GUC parameters.

Value range: Boolean

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

NOTICE: Enable the maintenance mode with caution to avoid MogDB 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 GUC parameters.

Value range: Boolean

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

Default value: on

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 MogDB. Similar to this parameter, the default_transaction_deferrable 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 GUC parameters.

Value range: Boolean

• on indicates that the execution of a transaction can be delayed.
• off indicates that the execution of a transaction cannot be delayed.

Default value: off

enforce_two_phase_commit

Parameter description: Specifies whether to forcibly use two-phase commit. This parameter is reserved for compatibility with earlier versions and is invalid in the current version.

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

Value range: Boolean

• on indicates that two-phase commit is forcibly used.
• off indicates that two-phase commit is not forcibly used.

Default value: on

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 GUC parameters.

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

replication_type

Parameter description: Specifies what nodes are deployed for the HA mode. The nodes can consist of a primary, a standby, and a secondary node; or consist of a primary and multiple standby nodes; or consist of a primary node.

This parameter is a POSTMASTER parameter. Set it based on instructions provided in Table 1 GUC parameters.

You are advised not to modify this parameter.

Value range: 0 to 2

• 0 indicates that the HA nodes consist of a primary, a standby, and a secondary node, This mode is not currently supported.
• 1 indicates that the HA nodes consist of a primary and multiple standby nodes. Full scene coverage, this value is recommended.
• 2 indicates that single host mode. This mode cannot expand the standby nodes.

Default value: 1