LMDB usage with long or variable length keys

[Alex V.]

I am new to key-value stores. I would like to use it like big persistent 
associative array and I want to be able to use long length keys. For 
example file path or URL. What technique should I use to implement such 
dictionary on top of LMDB? Probably some kind of hashing and collision 
resolution? Or just recompile with MDB_MAXKEYSIZE=2047 or something like 
this? Or LMDB is a wrong tool for this job?