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I have an Amazon DynamoDB table which is used for both read and write operations. Write operations are performed only when the batch job runs at certain intervals whereas Read operations are happening consistently throughout the day.

I am facing a problem of increased Read latency when there is significant amount of write operations are happening due to the batch jobs. I explored a little bit about having a separate read replica for DynamoDB but nothing much of use. Global tables are not an option because that's not what they are for.

Any ideas how to solve this?

jarmod
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Tyr1on
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    Which Read/Write Capacity Mode are you using for the table? Provisioned? On-Demand? Is autoscaling enabled? Are you performing strongly consistent reads, or eventually consistent reads? Have you considered using DynamoDB Accelerator (DAX)? Or perhaps an in-memory cache in your application to reduce the number of reads sent to DynamoDB? – Mark B Aug 31 '21 at 17:44

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Going by the Dynamo paper, the concept of a read-replica for a record or a table does not exist in Dynamo. Within the same region, you will have multiple copies of a record depending on the replication factor (R+W > N) where N is the replication factor. However when the client reads, one of those records are returned depending on the cluster health.

Depending on how the co-ordinator node is chosen either at the client library or at the cluster, the client can only ask for a record (get) or send a record(put) to either the cluster co-ordinator ( 1 extra hop ) or to the node assigned to the record (single hop to record). There is just no way for the client to say 'give me a read replica from another node'. The replicas are there for fault-tolerance, if one of the nodes containing the master copy of the record dies, replicas will be used.

I am researching the same problem in the context of hot keys. Every record gets assigned to a node in Dynamo. So a million reads on the same record will lead to hot keys, loss of reads/writes etc. How to deal with this ? A read-replica will work great because I can now manage the hot keys at the application and move all extra reads to read-replica(s). This is again fraught with issues.

Pradeep Banavara
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