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Key-value data stores are databases that use associative arrays or dictionaries as the basic datatype. Keys are data used to look up values. An example of key-value data is shown in Table 1.7, which displays a mapping from names of machine instances to names of partitions associated with each instance.

Table 1.7 Examples of key-value data

Key	Value
Instance1	PartitionA
Instance2	PartitionB
Instance3	PartitionA
Instance4	PartitionC

Key-value data stores are simple, but it is possible to have more complex data structures as values. For example, a JSON object could be stored as a value. This would be reasonable use of a key-value data store if the JSON object was only looked up by the key, and there was no need to search on items within the JSON structure. In situations where items in the JSON structure should be searchable, a document database would be a better option.

Cloud Memorystore is a fully managed key-value data store based on Redis, a popular open source key-value datastore. As of this writing, Cloud Memorystore does not support persistence, so it should not be used for applications that do not need to save data to persistent storage. Open source Redis does support persistence. If you wanted to use Redis for a key-value store and wanted persistent storage, then you could run and manage your own Redis service in Compute Engine or Kubernetes Engine.