How does Dynamodb Sort the query results when there is no range key avaialble?

Question

I've a Dynamodb table that contains only a hash key (partition key). There is no range key (sort key) for this table. Hash key is a numeric value (eg:- 1,2,3... N) When I query or Scan this table, which order they send the results in? If there is a range key, it obviously sorts the results in ascending order based on the range key value. But in this case without a RANGE KEY, how does it behave?

Answer 1

DynamoDB does not offer any ordering guarantees (implicit or explicit) for scanning items from a table. The items are more or less returned in the order that the internal hashing function maps items to partitions of the table but there are no implicit or explicit ordering guarantees.

Even with a sort key, the ordering is implied only within the items of the same partition key. So even if you had a range key on the table, that would only allow you to query items in order for a specific hash key at a time.

If you need to order all items in a table then you have a few options:

• scan all data and order on the client
• create a global secondary index with a common value for partition key for all items and query that
• design a complementary storage layer to provide ordering

It's important to stress that the first two options above are only good for relatively small tables. Once you reach about 10GB in the table having a GSI with a common key will act as a significant bottle-neck and of course scanning and order the whole table becomes problematic as well.