Query a range of primary keys in dynamodb

2
votes

I want to make sure I get this right,
Based on what I've read so far, you can NOT query a range of primary keys in dynamodb,
like if you have a primary key which is number like the phone number of your customers, you can not get items with primary keys larger than 3010000000 or between 3010000000 and 3020000000
to make it clear, I am not talking about the range key, my questions is about the primary key itself,

so if this is true, there are lots of use cases, like items between dates, users registered after some point, and... , that requiers either table scans,

is this correct?

EDIT: OK, one solution that comes to mind, would be to use only one dummy hash_key for primary key and insert the real key (like phone numbers above) as range keys, does this work?

2
amazon-dynamodb

2 Answers

8
votes

Yes, you can not get a range of hash_key with DynamoDb. But this does not mean you are stuck with your use case.

Let's take the 'dates' use case and say your are building a logging application. You are likely to get lots of records each day.

If you use the day as the hash_key, you can put the full timestamp as the range_key. This way, you can split your query into chunks and get what you want.

Of course, to get the optimal results, you will need to know well the kind of queries. For example, what is the typical range ? With DynamoDb, as well as other key:value store, you most of the time model your data with query in mind, unlike SQL when you model with only data in mind.

Of course, if your items spans on larger/shorter range, just adapt this system.

Concerning the "all under the same dummy hash_key" sounds like a terrible idea. Sorry. I am not a hundred percent sure how it really works but I know DynamoDB does some sharding across so called partitions. I believe 1 hash_key <=> 1 partitions. Moreover, If read closely the documentation, you'll notice that the provisionned throughput is splited evenly between the partitions so that each partitions is only allocated a fraction of what you pay for.

0
votes

Without modifying the keys of your primary DynamoDB table, you can add a GSI with a constant partition key and your primary table's partition key as its sort key.

This will enable you to query on the index's sort key and use the resulting partition keys to get the data you're looking for.