AnonimaUzanto / py-lmdb

Universal Python binding for the LMDB 'Lightning' Database

This is a universal Python binding for the LMDB ‘Lightning’ Database.

See the documentation for more information.

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This is a fork especially for the use with the Monero project.

It is aimed at interacting with the Monero's blockchain database implemented in lmdb.

The main difference is the use of dupsort and dupfixed databases, that need custom compare functions by setting mdb_set_dupsort.

The implementaton of those compare functions is hardcoded - as can be found in the Monero source code (/src/blockchain_db/lmdb/db_lmdb.cpp):

• mdb_set_dupsort can compare 32 bit hashes by using set_dupsort_hash32().
  • The sort key is the transaction hash in database b"block_heights" (See example below).
  • Monero source code: int BlockchainLMDB::compare_hash32(const MDB_val *a, const MDB_val *b).
• mdb_set_dupsort can compare 64 bit integers by using set_dupsort_uint64().
  • The sort key is the block height in database b"block_info".
  • Monero source codeint BlockchainLMDB::compare_uint64(const MDB_val *a, const MDB_val *b).

Some databases require a dupsort using compare_hash32, some use compare_uint64.

Example:

env = lmdb.open("/some_path/Monero/lmdb", subdir=True, lock=False, readonly=True, max_dbs=10)
block_heights_db = env.open_db(b"block_heights", integerkey=True, dupsort=True, dupfixed=True)
with env.begin(db=block_heights_db) as txn:                                                                                  
    txn.set_dupsort_hash32(db=block_heights_db)
    if cursor.set_key_dup(key=b'\x00\x00\x00\x00\x00\x00\x00\x00', value=b'\x0b\x1d\x88\xb1\xea\xe9\x8a\xea\xc2\xb7\xe6\xb1V\xdd\\\xac\xc20\xc4\x88\x92E\x84\x85\t\x16\xde\xea\xf2\xac8\xd1*\xfe\x1f\x00\x00\x00\x00\x00')):
        print(cursor.item())
    else:
        print("Nothing found.")

The implementation only works with lmdb.cpython or LMDB_FORCE_CPYTHON=1.

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CI State

Python Version Support Statement

This project has been around for a while. Previously, it supported all the way back to before 2.5. Currently py-lmdb supports Python 2.7, Python >= 3.5, and pypy.

Python 2.7 is now end-of-life. If you are still using Python 2.7, you should strongly considering porting to Python 3.

That said, this project will continue to support running on Python 2.7 until Github Actions remove support for it.