Restrictions on the DR Instance
After a DB instance serves as a DR instance, some basic functions are unavailable and some monitoring metrics cannot be reported. This section describes the restrictions on the DR instance.
Restrictions on the Primary Instance
After a DR relationship is established, the DR instance only allows for storage scaling, specifications change, rebooting, and parameter modification. The basic functions of the primary instance have the following restrictions:
Function |
Supported by the Primary Instance During DR |
---|---|
Rebooting an instance |
Yes |
Modifying parameters |
Yes |
Applying parameters |
Yes |
Resetting a password |
Yes |
Performing a full backup |
Yes |
Creating a differential backup |
Yes |
Deleting a backup |
Yes |
Modifying the backup policy |
Yes |
Restoring data to the original instance |
No |
Restoring data to a new instance |
Yes |
Scaling up storage space |
Yes |
Scaling down storage space |
Y |
Adding nodes (only for distributed instances) |
No |
Changing instance specifications (only for centralized instances) |
Yes |
Upgrading a minor version |
Yes |
Viewing slow query logs |
Yes |
Viewing metrics |
Yes |
Deleting an instance |
No |
Deleting an automated backup |
N/A |
Rebuilding a deleted instance from the recycle bin |
N/A |
Backing up and restoring data in a single table |
Yes |
Balancing an instance |
Yes |
Querying the disk usage |
Yes |
Creating a database |
Yes |
Querying a database |
Yes |
Creating a schema and user |
Yes |
Deleting a schema and user |
Yes |
Performing database operations |
Yes |
Using DAS for database management |
Yes |
Repairing a node |
Yes |
Replacing a node |
Yes |
Forcibly starting a minority of AZs |
No |
Resuming AZs |
No |
Switching AZs |
Yes |
Resetting configurations (for DR) |
Yes |
Adding replicas |
No |
Managing tags |
Yes |
Binding an EIP |
Yes |
Restrictions on Monitoring Metrics
After the DR relationship is established, some monitoring metrics of the DR instance are unavailable. The following table lists the monitoring metrics of the DR instance.
If the deployment model of an instance is 1 primary + 1 standby + 1 log, the log node does not have a data disk, and the following node-level metrics related to data disks cannot be displayed for the node:
- Disk IOPS
- Disk Write Throughput
- Disk Read Throughput
- Time Required for per Data Disk Write
- Time Required for per Data Disk Read
Category |
Sub-category |
Metric |
Displayed for Distributed DR Instance |
Displayed for Centralized DR Instance |
---|---|---|---|---|
Instance level |
- |
Used Instance Disk Size |
Yes |
No |
Total Instance Disk Size |
Yes |
No |
||
Instance Disk Usage |
Yes |
No |
||
Deadlocks |
No |
No |
||
Response Time of 80% SQL Statements |
No |
No |
||
Response Time of 95% SQL Statements |
No |
No |
||
Buffer Hit Rate |
No |
No |
||
Node level |
- |
CPU Usage |
Yes |
Yes |
Memory Usage |
Yes |
Yes |
||
Data Write Volume |
Yes |
Yes |
||
Outgoing Data Volume |
Yes |
Yes |
||
Disk IOPS |
Yes |
Yes |
||
Disk Write Throughput |
Yes |
Yes |
||
Disk Read Throughput |
Yes |
Yes |
||
Time Required for per Data Disk Write |
Yes |
Yes |
||
Time Required for per Data Disk Read |
Yes |
Yes |
||
Swap Memory Usage |
Yes |
Yes |
||
Total Swap Memory |
Yes |
Yes |
||
IOPS Usage (This metric applies only to nodes that use EVS disks.) |
Yes |
Yes |
||
Disk I/O Bandwidth Usage (This metric applies only to nodes that use EVS disks.) |
Yes |
Yes |
||
Component level |
CN |
User Logins, User Logouts, Lock Waiting Session Rate, Active Session Rate, CN Connections, User Committed Transactions, User Rollback Transactions, Background Committed Transactions, Background Rollback Transactions, Average Response Time of User Transactions, User Transaction Rollback Rate, Background Transaction Rollback Rate, Data Definition Language, Data Manipulation Language, Data Control Language, DDL and DCL Rate, Data Volume to Be Flushed to Disks, Physical Reads per Second, Physical Writes per Second, Online Sessions, Active Sessions, Online Session Rate, Used Dynamic Memory, Dynamic Memory Usage, Maximum Execution Duration of Database Transactions, Idle Transactions, Slow SQL Statements in the System Database, Slow SQL Statements in the User Database, and Xlog Rate |
No |
N/A |
Primary DN |
Used Disk Size, Total Disk Size, Disk Usage, Data Volume to Be Flushed to Disks, Physical Reads per Second, and Physical Writes per Second |
N/A |
N/A |
|
Standby Redo Progress, User Logins, User Logouts, Lock Waiting Session Rate, Active Session Rate, User Committed Transactions, User Rollback Transactions, Background Committed Transactions, Background Rollback Transactions, Average Response Time of User Transactions, User Transaction Rollback Rate, Background Transaction Rollback Rate, Data Definition Language, Data Manipulation Language, Data Control Language, DDL and DCL Rate, Online Sessions, Active Sessions, Online Session Rate, Used Dynamic Memory, Dynamic Memory Usage, Size of WALs Retained in the Replication Slot, and Xlog Rate |
N/A |
N/A |
||
Standby DN |
Used Disk Size |
Yes |
Yes |
|
Total Disk Size |
Yes |
Yes |
||
Disk Usage |
Yes |
Yes |
||
Primary Node Flow Control Duration |
No |
No |
||
Standby Node RTO |
No |
No |
||
Standby Node Redo Progress |
No |
N/A |
||
Lock-Waiting Session Rate |
No |
No |
||
Active Session Rate |
No |
No |
||
Online Session Rate |
No |
No |
||
Online Sessions |
No |
No |
||
Dynamic Memory Usage |
No |
No |
Restrictions on Major Version Upgrade in the DR Mode
Only gray upgrade is supported.
- Upgrade the primary instance. Ensure the upgrade is not submitted.
- Upgrade the DR instance.
- Submit the upgrade of the DR instance first and then the primary instance until the DR instance upgrade is complete
Restrictions on Minor Version Upgrade in the DR Mode
Only gray upgrade is supported.
- Upgrade the primary and DR instances at the same time.
- Submit the upgrade of the DR instance first and then the primary instance.
- Before submitting the upgrade of the DR instance, ensure that the upgrade of primary instance is complete.
- Submit the upgrade of the DR instance first and then the primary instance.
- If the DR instance upgrade has been submitted, the upgrade of the primary instance cannot be rolled back.
- During the upgrade of the primary and DR instances, do not perform a switchover.
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