EntityManager.find() with filter+limit can spawn thousands of recursive sequential queries

[smcroskey]

Because of how explicit limits are applied, we've run into situations where a single find() call can spawn thousands of sequential queries internally. With a small enough limit, and with a filter that would ordinarily return no results, it effectively turns into a very slow scan of a partition. This is fairly unexpected behavior when specifying an explicit limit; furthermore, there's no way for TypeDorm to provide a limit directly to the DynamoDB query call without also triggering this potential runaway recursive query.

Suggestions:

• There should be an option to specify whether the limit should be a DyanmoDB-only limit (IOW, the number results returned could be less than the limit provided, and guarantee only one query is made) or the TypeDorm notion of a limit (where it guarantees continually querying until either the limit is reached or the results are exhausted)
• When using the TypeDorm notion of limit, recursive queries could potentially use exponentially increasing limits (or perhaps no limit at all) so that when a small limit is provided, it doesn't turn into a flood of sequential internal queries returning 0 results
• Additionally, it may make sense to use a reasonable cap so that a single find(...) call will not spawn more than X queries internally, or look at more than X records (like a query/scanLimit). E.g. 2000+ queries from a single find(...) is probably never intended.

[m-szaf]

An additional suggestion would be providing a RCU limit which describes the max read capacity units the find operation should use before stopping - regardless of reaching a provided limit. This may be better as it is more predictable in terms of cost.

[m-szaf]

👋 @whimzyLive Feature add PR for this issue is here 🙏