Keys iterator of the store::UnorderedMap consumes gas while skipping (skip). FreeList iterator is not lazy.

[fadeevab]

skip is not cheap (FreeList::Iterator::skip) because it's not lazy, it reads every value while moving to the nth position to figure out whether a slot is occupied or not. Skipping over a few thousand elements may be impossible because gas will be consumed earlier.

~30TGas to skip 300 elements

So if you have 10k accounts in the map, you can't practically skip 2-3k accounts, e.g. you can't view/print most of the map.

[fadeevab]

@frol Iterating by keys is broken. Ideally, it's better to:

1. Fix the map (although, I don't see how),
   - OR -
2. Rename the current store::UnorderedMap to "something else map", e.g. FragmentedMap.
3. pop operation could be added for fast O(1) removals to the original UnorderedMap.

[ruseinov]

I suggest to combine this with that. Let's answer questions there, estimate and proceed.

[fadeevab]

@ruseinov yes, agree

[frol]

Closing as "duplicate"