nstance status before changing the billing mode.
Why Is Available Memory of Instances Less than Total Memory and Why Is Memory Usage of Instances Greater than Zero?
The available memory is less than the total memory because some memory is reserved for system overhead and data persistence. DCS instances use a certain amount of memory for Redis-server buffers and internal data structures. This is why memory usage of DCS instances is greater than zero.
Will Cached Data Be Retained After an Instance Is Restarted?
By default, the instances support AOF persistence, which cannot be disabled. Data is retained after these instances are restarted.
Does Redis API Support Fuzzy Query Using Methods Other than the Keys Command?
In case of a large amount of data, the Keys operation blocks subsequent read/write requests if used for query. Redis provides SCAN, and SSCAN and HSCAN for the set type. It returns a fixed number according to the configured number parameter. This way, not all matched data is returned at the same time like the Keys command, and Redis will not slow down.
How Do I Find Big Keys in Redis?
It is recommended not to use big keys as much as possible, because the main thread of Redis will be blocked for operating on big keys. The following shows how to find big keys used in services. Run the redis-cli command with the --bigkeys option (redis-cli -h -p -a --bigkeys). After the command is executed, a statistical analysis is performed on the size of the key value in the database, and it will generate the information of the largest big key in each data type. For example, for String type, it will output the big key with the largest byte length, and for the set type, it will output the big key with the most elements. Note: For a big key of the set type, the set with the most elements is not necessarily the one with the largest memory footprint.
You can also use the Redis RDB snapshot file analysis tool to analyze the memory usage of all keys in instances. Link: https://github.com/sripathikrishnan/redis-rdb-tools?spm=a2c4g.11186623.0.0.140745d6UhJnC6
How Do I Find Hot Keys in Redis?
Starting from Redis 4.0, the Redis-CLI client provides the --hotkeys parameter (redis-cli -h -p -a --hotkeys) to query and analyze the hot keys for a running instance. Note: The --hotkeys parameter can be used only when the Redis instance uses the LFU memory eviction policy.
How Do I Check for Memory Fragments?
Redis is an in-memory database, and memory utilization determines its operation efficiency. To monitor the real-time memory usage, Redis provides the info memory command to query the memory usage. mem_fragmentation_ratio indicates the current memory fragmentation ratio of Redis. The memory fragmentation ratio is calculated based on the following formula: mem_fragmentation_ratio = used_memory_rss/used_memory. used_memory_rss is the memory size actually used by users and used_memory is the allocated memory size. For example, a key actually uses 6 bytes of memory space, but the Redis memory mechanism allocates 8 bytes. The memory fragmentation ratio is displayed on the metric monitoring page. You can query the history memory fragmentation ratio.
What Is the Size of Each Database in Redis and How Can I Choose Databases?
Each DCS Redis instance has 256 databases named from DB0 to DB255. The size of each database is not restricted. But the available database space is limited by the overall space of the Redis instance.
You can run the SELECT command to switch among different databases. For example, to switch to DB108, you can run the following command:
Why Is Available Memory of Instances Less than Total Memory and Why Is Memory Usage of Instances Greater than Zero?
The available memory is less than the total memory because some memory is reserved for system overhead and data persistence of active/standby instances.
Why Can't I Delete an Instance?
You can only delete a running instance.
Is Cross-AZ Deployment Supported?
Standard active/standby instances and clusters support cross-AZ deployment. You can select cross-AZ deployment when creating an instance.
Can I Change the AZ for an Instance?
No. You can only create a new instance to change the AZ.
Do Redis Instances Support Read-write Separation?
No.
How Can I Secure My DCS Redis Instances?
Access control: Enable password authentication in Redis. You can set a strong password to restrict access to Redis instances. Specifically, you can set a password in the requirepass parameter of the Redis configuration file and use the AUTH command for authentication on the client. In addition, configure the bind parameter to limit allowable IP addresses and ensure that only trusted clients can access Redis.
You can also place a Redis instance in a secure network environment. For example, use a firewall or security group to set proper network policies that restrict access to Redis ports. This way, only trusted hosts or networks are allowed to access Redis instances.
How Can I Estimate the Redis Memory Footprint?
For details, see Redis Official Website.
Why Is the Status of an Instance Displayed as "Frozen"?
Generally, the Frozen status is displayed because it is a subscription-based instance and is not renewed after expiration. Please renew your instance in time to avoid data loss.
What Is the Connection Address of an Instance?
The connection address of an instance adopts a uniform format: virtual IP+ fixed port. After capacity expansion, the virtual IP address automatically switches to the new VM. The IP address remains unchanged for applications and you are not required to change the application code. You can check the connection address on the console. For details, see Connection Addressees.
What Is the Expiration Time of an Instance?
A subscription-based instance expires at the end of a calendar month. A pay-as-you-go instance expires when the resources are exhausted.
What Are the Supported Instance Types?
There are four types of instances, namely, stand-alone and active/standby instances, and stand-alone and active/standby clusters.
What is the Maintenance Time for an Instance?
We recommend that you set the maintenance window to off-peak hours based on your business requirements. This prevents interruptions to your business.
What Are the Supported Functions of Instance Application Data Management?
On the instance data management menu, the data of different database groups is displayed on pages. On these pages, you can query the total number of keys in a database group, and add, delete, change and view the page information for a single key.
What Is the Size of the Available Memory for Instances?
Some resources are occupied by the system. As a result, the memory available for Redis instances is smaller than the standard value. You are advised to expand the capacity when 80% of Redis memory is used up, and set the expiration time for keys to release memory properly.
What Is the Possible State of an Instance?
Possible states: Enabling, Running, About to Expire, and Expired.
Why Is the Frontend Empty in the Instance List?
For stand-alone and active/standby instances, the application directly connects to Redis nodes through a virtual IP without an intermediate proxy layer. Therefore, the access cluster in the instance list is empty.
What Is the Relationship Between an Instance Name and an Instance ID?
An instance ID is the unique identifier of a Redis instance, and an instance name is the alias of the instance. In the new version, you can change the instance name but cannot change the instance ID.
Is the Processing Method for Instances in Different Billing Modes the Same After Unsubscription?
If you unsubscribe from a subscription-based instance, the instance will be frozen and will be automatically released after 15 days by default. A pay-as-you-go instance is released immediately after unsubscription.
How Does the System Distribute the Slots in a Single Node or Cluster?
The slots of stand-alone and active/standby instances range from 0 to 16383. A cluster has 1638 slots evenly distributed among Redis shards.
How Do I Deal with Errors when Using redis_exporter?
You can run the redis_exporter command and resolve the problems according to the error message returned.
Does Redis Have Back-end Management Software?
No. You can view relevant performance data on the monitoring page of the console. For details, see Product Monitoring.
Why Does an OOM Error Occur During a Redis Connection?
Error in execution; nested exception is io.lettuce.core.RedisCommandExecutionException: OOM command not allowed when used memory > 'maxmemory' is returned during a Redis connection. An out-of-memory (OOM) error indicates that the maximum memory is exceeded. You can check the memory usage on the resource monitoring page.
What Should I Do to Handle a Timeout Error when Reading Data from Redis?
l Check whether the timeout value is set too small.
l Check whether the error is returned after an operation is performed on a big key. It is recommended that the key size be no greater than 10 KB.
l Adjust the PingConnectionInterval parameter based on the error information.
Are External Extensions, Plugins, or Modules Supported?
Currently, they are not supported.
What Are Hash Tags? What Are the Functions of Hash Tags?
Redis uses hash tags, a special tagging mechanism, to store the keys with the same hash slot on the same Redis node. Hash tags ensure that associated keys are mapped to the same hash slot, which improves the performance and availability of Redis clusters in certain scenarios. Keys with the same hash tag are assigned to the same slot in a Redis cluster to ensure that these keys are stored on the same Redis node. This helps store associated data close to each other and improves the efficiency of data access.
Can I Customize or Change the Port for an Instance?
It is not supported currently. You can view port information on the instance details page of the console. For details, see Viewing Instance Information.
Can I Change the Access Address of an Instance?
It is not supported currently. You can view the access address on the console. For details, see Viewing Connection Addresses.
Why Does It Take a Long Time to Start a Cluster Instance?
If a large amount of data is continuously written into an instance during startup, the state and synchronization processes will be affected. You are recommended to start writing data to an instance only after the instance has been started.
How Do I View the IP Addresses of Nodes in a Redis Cluster?
Run the CLUSTER NODES command. The information about all the nodes in a Redis cluster is displayed, including node IDs, IP addresses and port numbers.