Layers:

LRU cache - exists if we know the answer, undef means "ain't there" Memcached PostgreSQL select PostgreSQL insert

add_layer

Adds a new layer to KV storage. Links it to the current layers as appropriate.

Takes a single parameter:

• $layer - the new layer to add

Returns $self.

remove_layer

Removes an existing layer to KV storage. Unlinks the other layers as appropriate.

Takes a single parameter:

• $layer - the new layer to add

Returns $self.