Feature request: add local cache to Idempotency persistence layer

[saragerion]

Use case

To improve performance, the Idempotency utility can be configured to use a local cache to store idempotency records.

Solution/User Experience

import { IdempotencyConfig } from '@aws-lambda-powertools/idempotency';

const config = new IdempotencyConfig({
  useLocalCache: true,
});

Optionally, the user can also set a max number of items to store in the cache before older ones start get evicted:

import { IdempotencyConfig } from '@aws-lambda-powertools/idempotency';

const config = new IdempotencyConfig({
  useLocalCache: true,
  localCacheMaxItems: 10, // defaults to 256
});

Use the Python implementation as reference and extend the BasePersistenceLayer.

The IdempotencyConfig class already supports the useLocalCache field. The localCacheMaxItems one is not yet implemented and should default to 256.

Below comments from @dreamorosi:

Contrary to Python, Node.js doesn't have a LRU Cache in its standard library. Looking at popular libraries there seem to be two options:

• lru_map 3.7M weekly downloads - last published 3 yrs ago - 27.9 kB unpacked size
• lru-cache 123M weekly downloads - last published 2 days ago - 638 kB

Both libraries appear to be extremely popular. The former, lru_map is a lot less popular than the other and hasn't been updated in a long time, however it has a small footprint when compared to the other alternative.

In terms of features, the lru-cache module has a wide range of features like TTL, retrieval functions from remote, etc. - all these features contribute to the significant size. On the other hand, lru_map only supports one config/feature: the ability to set a maximum of items to keep in the cache.

Our currently published Powertools utilities range between 70 and 110 kB. Given that lru_map supports exactly the features that we need, has zero dependencies, and a relatively stable implementation, I'm inclined to recommend this module over the other larger and more feature complete one.

Alternative solutions

No response

Acknowledgment

• This feature request meets Lambda Powertools Tenets
• Should this be considered in other Lambda Powertools languages? i.e. Python, Java

[github-actions]

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