Please add a way to list named databases

[NightTsarina]

Hi,

I have been trying to find a way to list all the named databases present in an environment, but neither here nor in the C library there seems to be any functionality to do so. The naive solution of iterating all keys in the unnamed database only works if you don't store any normal keys there. The closest I've got is to try and db_open every key found, but that would not be practical in the general case, and I am not sure if it would work depending on the flags used to create the DB.

The only reliable way I've found to do this requires accessing the internal C structures and check the Node flags ((node->mn_flags & (F_DUPDATA|F_SUBDATA)) != F_SUBDATA) as the mdb_dbi_open function does (code).

The mdb_stat tool has a way to iterate databases, which seems to be to iterate all keys in the main DB and check for the absence of a \x00 value (?): https://sources.debian.org/src/lmdb/0.9.24-1/libraries/liblmdb/mdb_stat.c/#L229

It would be great to have this functionality added to the python bindings.

[jnwatson]

While it isn't explicitly said anywhere, my opinion is that it is bad form to use both named databases and populate keys in the main database.

Regardless, your point stands. I agree this would be useful functionality.