Create policy based on size

[rturk]

Constrains in mobile phones are mostly related to storage. Discuss Create policy based on size X bytes (GB, MB, KB) ...

[timfpark]

Yup - makes sense - would love a PR for this. I mostly used count in my initial implementation because the items I am storing in my app are all the same size...

[vincentjames501]

+1

[DarkMatterMatt]

I'd like to PR this.

I see a two main ways to do it:

1. Have a single _size entry (similar to _lru) that gets updated every time an entry is added/removed. This would add ~50% of the number of backend calls when adding/removing items because of having to get/set _size as well as _lru. When removing the item we will also have to backend.getItem the value (as well as backend.removeItem) in order to update _size.
2. Track the _size and _lru in a single _metadata entry (e.g. metadata = { size: 0, lru = [[key1], [size1]] }). This requires more code changes, but I think it would result in a better implementation. When removing key1 we could just subtract size1 from the current size.