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. This parameter is reserved and does not take effect in this version. 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

enable_show_any_tuples

Parameter description: This parameter is available only in a read-only transaction and is used for analysis.

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

pgxc_node_name

Parameter description: Specifies the name of a node.

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

When a standby node requests to replicate logs on the primary node, if the application_name parameter is not set, the pgxc_node_name parameter is used as the name of the streaming replication slot of the standby node on the primary node. The streaming replication slot is named in the following format: Value of this parameter_IP address of the standby node_Port number of the standby node. The IP address and port number of the standby node are obtained from the IP address and port number of the standby node specified by the replconninfo parameter. The maximum length of a streaming replication slot name is 61 characters. If the length of the concatenated string exceeds 61 characters, the truncated pgxc_node_name will be used for concatenation to ensure that the length of the streaming replication slot name is less than or equal to 61 characters.

Note: After this parameter is modified, the database instance will fail to be connected. You are advised not to modify this parameter.

Value range: a string

Default value: current node name

enable_defer_calculate_snapshot

Parameter description: Specifies the delay in calculating xmin and oldestxmin. Calculation is triggered only when 1000 transactions are executed or the interval is 1s. If this parameter is set to on, the overhead of calculating snapshots can be reduced in heavy-load scenarios, but the progress of oldestxmin is slow, affecting tuple recycling. If this parameter is set to off, xmin and oldestxmin can be calculated in real time, but the overhead for calculating snapshots increases.

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

Value range: Boolean

• on indicates that snapshots xmin and oldestxmin are calculated with a delay.
• off indicates that snapshot xmin and oldestxmin are calculated in real time.

Default value: on

async_submit

Parameter description: You can control at session level whether to use transaction asynchronous commit or not. This option is only available when "enable_thread_pool = on" and "synchronous_commit" are valid if "off" is not selected. .

Value range: Boolean

• on indicates that transaction asynchronously commit is enabled, all transaction commits on this session will be completed asynchronously.

• off indicates that all transactions on that session are committed according to the original logic.

Default value: off