Note: If you are looking for the Memorystore for Redis Cluster documentation,seeAbout scaling instance capacity.

This page describes how your Memorystore for Redis instance behaves during scaling.To learn how to scale a Redis instance, seeScaling Redis Instances.

Depending on the instance's tier, scaling an instance has performance andstorage implications for your application. There are also some limitations toscaling instances based on the amount of memory that is currently in use. Thispage describes how scaling an instance can affect your application and whenyou can scale an instance.

Note: When you scale an instance, there might be a gap of 3-5 minutes when thecore metricsfor the instance don't appear. During this time, the instance is available. Afterthe time interval completes, the metrics appear.

Best practices for scaling an instance

• For Standard Tier instances, to increase the speed and reliability ofyour scaling operation, scale your instance during periods of low instancetraffic. To learn how to monitor instance traffic, seeMonitoring Redis instances.

• When reducing a Standard Tier instance's capacity, you must choose a sizegreater than the amount of data being stored or scaling fails.

  • For example, if your have a 10 GB instance that has 5.5 GB of data storedin it, you can resize the instance to a minimum of 6 GB. The amount of storageyour instance uses is visible on its details page in theGoogle Cloud console.

Instance scaling behavior

Data is preserved during scaling for both Basic and Standard Tier instances.During scaling the instance undergoes a short connection reset of a coupleminutes, or less. Applications should incorporate retry logic in the code to beable to reconnect to the instance. The IP address and connection string remainthe same.

Because of the short term connection break, there may be a small amount of staleor inconsistent data that didn't write or update to the cache for the shortamount of time the instance was unavailable.

If you issue a write during the connection break, Memorystorereturns the errorREADONLY You can't write against a read only replica. Thiserror is transient, and only lasts a few seconds. It resolves once the scalingoperation completes.

Write load when scaling

You should scale an instance during a period of low instance traffic to minimize the performance impact on your application. A high write load, or high memory pressure, can cause an scaling operation to take significantly longer and can cause the operation to fail. For more information seeScaling and version upgrade operations.

Expired keys

When you scale a Standard Tier instance, expired keys are not synced. If you haveexpired keys in your Redis instance before you scale, you will have fewer keysafter the instance is scaled.