Product-related FAQs

1. What is the relationship between ultimate RTO, parallel recovery, and standby node readability?

Answer:

The configurations of ultimate RTO, parallel recovery, and standby node readability are as follows:

• Ultimate RTO: recovery_parse_workers indicates the number of Xlog threads parsed during parallel recovery. recovery_parallelism indicates the actual number of Xlog threads during parallel recovery. When recovery_parse_workers is greater than 1, ultimate RTO recovery is implemented. Only when both recovery_parse_workers and recovery_parallelism are set to a value greater than 1, can parallel recovery be implemented.
• Parallel recovery: recovery_max_workers specifies the maximum number of threads for parallel recovery. recovery_parallelism specifies the actual number of threads for parallel recovery. If the value of recovery_max_workers is greater than 1, parallel recovery is configured. However, only when recovery_max_workers and recovery_parallelism are set to a value greater than 1, can parallel recovery be implemented.
• Standby node readability: hot_standby indicates that a hot standby node can be read during recovery. If the value of hot_standby is true, the standby node can be read.

Parallel recovery is a file-level parallel redo, and the ultimate RTO is a data block-level parallel recovery. Parallel recovery is compatible with standby node readability, but ultimate RTO is incompatible with standby node readability. During configuration of preceding parameters, code check (with CheckExtremeRtoGUCConflicts) is performed. If recovery_parse_workers is set to a value greater than 1 and hot_standby is set to true, an error will be reported.

2. How can I select a candidate primary node for primary/standby switchover when the standby node cannot be read in the ultimate RTO scenario?

Answer:

The standby node cannot be read only when the RTO is ultimate. In serial recovery and parallel recovery, the standby node can be read. If the ultimate RTO is used, only the synchronous mode can be configured, and a node is selected randomly as the primary. After the synchronous mode is used, the data on all nodes is the same.

3. What is the function of the template database? Which tables are contained in the template database?

Answer:

The template database provides a method of quickly creating a database. When creating a database, you can specify the TEMPLATE parameter to create a database by copying a template database.

The template database does not contain any user table. You can view the attributes of the template database in the PG_DATABASE system catalog.

4. When openGauss supports physical replication, does the standby node replay logs by page in parallel mode?

Answer:

openGauss supports two parallel recovery modes: file-level recovery and page-level recovery.