Application Lossless and Transparent

alt_grace_period

Parameter description: alt_grace_period indicates the period during which the data of the source version is not reclaimed after a session is disconnected unexpectedly or a DN is promoted to primary during an unplanned application of the lossless and transparency feature. During this period, data records of the source version are retained to support replay of executed statements using snapshots of the source version. After alt_grace_period expires, the driver uses the snapshot of the source version to replay the executed statements. The original snapshot may become invalid.

Parameter type: integer.

Unit: second

Value range: 0 to 3600

• 0 indicates that the lossless and transparent setting is disabled for unplanned applications.
• A positive number indicates the time when the data of the source version is not reclaimed after the session is disconnected abnormally or the DN is promoted to primary through a switchover. When the value of this parameter is exceeded, the system does not reserve the data of the source version for this feature.

Default value: 0

Setting method: This is a POSTMASTER parameter. Set it based on instructions provided in Table 1. For example, if this parameter is set to 60 without a unit, it indicates 60s. If this parameter is set to 1min, it indicates 1 minute. The unit must be s, min, h, or d if required.

Setting suggestion: Set this parameter to the default value when the lossless and transparent feature of unplanned applications is not used. If the lossless and transparent feature is used for unplanned applications, you are advised to set this parameter to 60 that is, 1 minute.

Risks and impacts of improper settings: If this value is too large, data of the source version will be stacked, affecting the storage space and query execution efficiency.