Parameters related to physical restore|V4.3.0| docs|Distributed Database

Parameters related to physical restore

Last Updated：2024-05-29 07:17:41 Updated

This topic describes the parameters in restore statements.

Parameters in the RESTORE statements

Syntax

Restore to a specified timestamp:

ALTER SYSTEM RESTORE dest_tenant_name FROM uri UNTIL TIME='timestamp' WITH 'restore_option' [WITH KEY FROM 'backup_key_path' ENCRYPTED BY 'password'] [DESCRIPTION [=] description];

Restore to a specified SCN:

ALTER SYSTEM RESTORE dest_tenant_name FROM uri UNTIL SCN=scn WITH 'restore_option' [WITH KEY FROM 'backup_key_path' ENCRYPTED BY 'password']  [DESCRIPTION [=] description];

Restore to the latest checkpoint:

ALTER SYSTEM RESTORE dest_tenant_name FROM uri WITH 'restore_option' [WITH KEY FROM 'backup_key_path' ENCRYPTED BY 'password'] [DESCRIPTION [=] description];

Cancel the restore of a tenant:

ALTER SYSTEM CANCEL RESTORE dest_tenant_name;

Parameters

Parameter	Description
dest_tenant_name	The name of the target tenant to which the data is to be restored.
uri	The data backup path `backup_data_dest` and log archive path `log_archive_dest` specified during restore. The value must contain at least one data backup path and one log archive path that are separated with a comma (`,`).
timestamp	The timestamp to which data is restored. Join the parameter name and value with an equal sign (`=`). The timestamp must be in the `YYYY-MM-DD HH24:MI:SS.FF` format, and the fractional part (`FF`) supports 0 to 6 decimal places, accurate to microseconds.
scn	The SCN to which data is restored. Join the parameter name and value with an equal sign (`=`).
restore_option	The restore options, including `pool_list`, `locality`, `primary_zone`, and `concurrency`. Separate the options with ampersands (`&`). We recommend that you set `locality` and `primary_zone` to the same values as those of the source tenant. Otherwise, load balancing may be performed after the tenant is restored and activated as the primary tenant, which compromises the performance. `pool_list`: Required. The name of the resource pool created for the tenant to be restored. Multiple resource pools must be separated with commas (,). `locality`: optional. The locality of replicas of the tenant to be restored, which must match the zone information of `pool_list` of the cluster where the tenant is located. To ensure homogeneity with the source tenant, we recommend that you set the number of full-featured replicas of the tenant to the same as that of the source tenant. By default, if this parameter is not specified, a full-featured replica is set for each zone in `zone_list` of the resource pool. Example: `locality='F@z1,F@z2,F@z3'` `primary_zone`: Optional. The preferred position of the leader of the tenant to be restored, which must match the settings of `pool_list` and `locality`. In other words, the value of this parameter must match the zone information and meet the requirement that the primary region have at least two Paxos members. To ensure homogeneity with the source tenant, we recommend that you set the number of primary zones with the top priority of the tenant to the same as that of the source tenant. If this parameter is not specified, the system randomly distributes leaders in the zones specified by `zone_list` of `locality`. Example: `primary_zone='z1'` `concurrency`: Optional. The degree of parallelism (DOP) for data restore. If `concurrency` is not specified, the `MAX_CPU` value assigned to the tenant is used as the default value. Example: `concurrency=50`
WITH KEY FROM 'backup_key_path' ENCRYPTED BY 'password'	The key backup information of the encrypted tenant. You need to specify the key backup information for a tenant restore only when the tenant is configured with transparent encryption. The parameters are described as follows: `backup_key_path`: the backup path of the key. `password`: the password that you set when you backed up the key.
description	The description. This parameter is optional.

Constraint for specifying the timestamp and SCN

The timestamp and SCN must be greater than or equal to the minimum restore SCN indicated by MIN_RESTORE_SCN in the data backup view CDB_OB_BACKUP_SET_FILES, and smaller than or equal to the maximum archive SCN indicated by CHECKPOINT_SCN in the log archive view CDB_OB_ARCHIVE_LOG. Log archiving may be interrupted. Therefore, you must consider inconsecutive ranges of logs when you specify the restore SCN. The restorable window may be discontinuous.

Assume that:

Two log archive rounds were initiated, with the round_id values of 1 and 2.
Three data backup jobs were initiated, which produced three valid data backup sets: full_backup_set_1, full_backup_set_2, and inc_backup_set_3.

The following figure shows the restorable window for physical restore. The right boundary of a data backup set is specified by MIN_RESTORE_SCN. For example, MIN_RESTORE_SCN of full_backup_set_1 corresponds to scn 300 in the figure. The right boundary of a log archive is specified by CHECKPOINT_SCN. For example, CHECKPOINT_SCN of round 1 corresponds to scn 500 in the figure.

Restorable window

Log archiving may be interrupted. Therefore, you must consider the inconsecutive time ranges when you calculate the restorable window. As a result, the restorable window is discontinuous. In the figure, the restorable window is [scn 300, scn 500] \∪ [scn 900, scn 1500].

Parameters in the restore performance tuning statement

Syntax

ALTER SYSTEM SET ha_high_thread_score =10 TENANT = mysql;

Parameters

Parameter	Description
ha_high_thread_score	The number of worker threads for the restore job queue.

Parameters in the RECOVER statements

Syntax

Replay logs to the specified timestamp:

ALTER SYSTEM RECOVER STANDBY [TENANT [=] tenant_name] UNTIL TIME='timestamp';

Replay logs to the specified SCN:

ALTER SYSTEM RECOVER STANDBY [TENANT [=] tenant_name] UNTIL SCN=scn;

Continuously replay logs from the archive source without specifying the end point:
```
ALTER SYSTEM RECOVER STANDBY [TENANT [=] tenant_name] UNTIL UNLIMITED;
```

Cancel a log replay:

ALTER SYSTEM RECOVER STANDBY TENANT [=] tenant_name CANCEL;

Parameters

Parameter	Description
tenant_name	The name of the tenant.
timestamp	The timestamp to which data is restored. Join the parameter name and value with an equal sign (`=`). The timestamp must be in the `YYYY-MM-DD HH24:MI:SS.FF` format, and the fractional part (`FF`) supports 0 to 6 decimal places, accurate to microseconds.
scn	The SCN to which data is restored. Join the parameter name and value with an equal sign (`=`).
UNLIMITED	Specifies to continuously replay logs from the archive source without specifying the end point.

Parameters in the ACTIVATE STANDBY statement

Syntax

ALTER SYSTEM ACTIVATE STANDBY TENANT tenant_name;

Parameters

Parameter	Description
tenant_name	The name of the standby tenant that is restored. You can use this statement to change the role of only one tenant at a time.