Use the same DynamoDB attribute as both HASH and RANGE key

Question

I have a DynamoDB that is indexed by a single numerical key. I'd like to be able to both retrieve items having a specific value of the key, and find its maximum value by querying and requesting a single item in inverse sorting order. When I try to define 2 indices as in the excerpt below on the same key I get the error 'Two keys can not have the same name'.

"KeySchema": [
  {
    "AttributeName": "logs",
    "KeyType": "HASH"
  },
  {
    "AttributeName": "logs",
    "KeyType": "RANGE"
  }
]

It's an integer, which the application increments by 1 every time it adds a new record. In SQL I would have used a SERIAL or AUTOINCREMENT style key for this. — Isac Casapu, Mar 14 '19 at 12:34

score 0 · Accepted Answer · answered Mar 14 '19 at 12:47

0

You could define your key schema with only the hash key, no range key

"KeySchema": [
  {
    "AttributeName": "logs",
    "KeyType": "HASH"
  }
]

To request an item using a specific 'logs' value, use GetItem.

To find the highest value you would need to perform a Scan. This would be a poor way to find the highest value as it would mean evaluating every item in your table. It would be slow and expensive.

You might want to reassess your approach. If you are simply trying to create unique IDs, this is not the right approach for DynamoDB. What you should do is:

Generate a long UUID
Do a GetItem to verify that the UUID is available. This is very cheap and fast in DynamoDB
Use the UUID

answered Mar 14 '19 at 12:47

F_SO_K

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The existing system, which I'm trying to improve, uses the ID as a hash-only key, and does a scan. – Isac Casapu Mar 14 '19 at 13:34
You could move to creating long random UUIDs and not effect the old data. Basically you replace the slow Scan with a very fast GetItem to check the random ID is available. – F_SO_K Mar 14 '19 at 13:38
I agree the current design is quite questionable, and this is why I'm exploring alternatives – Isac Casapu Mar 14 '19 at 14:58
Does this answer your question? – F_SO_K Mar 14 '19 at 15:14
I was hoping for something else, but I accept it as it does appear to represent industry best practice. – Isac Casapu Mar 14 '19 at 15:31

Use the same DynamoDB attribute as both HASH and RANGE key

1 Answers1