This topic describes the limits on data types and some features of ApsaraDB for Redis.
Item  Description 
List data type  The numbers of lists and elements in a list are unlimited. The maximum size of each element is 512 MB. We recommend that the number of elements in a list is less than 8,192. The maximum value length is 1 MB. 
Set data type  The numbers of sets and elements in a set are unlimited. The maximum size of each element is 512 MB. We recommend that the number of elements in a set is less than 8,192. The maximum value length is 1 MB. 
Sorted set data type  The numbers of sorted sets and elements in a sorted set are unlimited. The maximum size of each element is 512 MB. We recommend that the number of elements in a sorted set is less than 8,192. The maximum value length is 1 MB. 
Hash data type  The numbers of hash tables and elements in a hash table are not limited. The maximum size of each element is 512 MB. We recommend that the number of elements in a hash table is less than 8,192. The maximum value length is 1 MB. 
Number of databases (DBs)  Each instance supports 256 databases. Note

Supported Redis commands  For more information, see Overview. 
Monitoring and alerting  ApsaraDB for Redis does not provide capacity alerts. You have to configure this feature in Cloud Monitor. For more information, see Alert settings. We recommend that you set alerts for the following metrics: instance faults, instance failover, connection usage, failed operations, capacity usage, write bandwidth usage, and read bandwidth usage. 
Policies to delete expired data 

Idle connection recycling mechanism  ApsaraDB for Redis does not automatically recycle idle connections to ApsaraDB for Redis. You can manage the connections. 
Data persistence policy  ApsaraDB for Redis uses the AOF_FSYNC_EVERYSEC policy and runs the fsync command at a onesecond interval. 