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# Copyright (c) 2016-2017, the ElectrumX authors
#
# All rights reserved.
#
# See the file "LICENCE" for information about the copyright
# and warranty status of this software.
'''Backend database abstraction.'''
import os
from functools import partial
import lib.util as util
def db_class(name):
'''Returns a DB engine class.'''
for db_class in util.subclasses(Storage):
if db_class.__name__.lower() == name.lower():
db_class.import_module()
return db_class
raise RuntimeError('unrecognised DB engine "{}"'.format(name))
class Storage(object):
'''Abstract base class of the DB backend abstraction.'''
def __init__(self, name, for_sync):
self.is_new = not os.path.exists(name)
self.for_sync = for_sync or self.is_new
self.open(name, create=self.is_new)
@classmethod
def import_module(cls):
'''Import the DB engine module.'''
raise NotImplementedError
def open(self, name, create):
'''Open an existing database or create a new one.'''
raise NotImplementedError
def close(self):
'''Close an existing database.'''
raise NotImplementedError
def get(self, key):
raise NotImplementedError
def put(self, key, value):
raise NotImplementedError
def write_batch(self):
'''Return a context manager that provides `put` and `delete`.
Changes should only be committed when the context manager
closes without an exception.
'''
raise NotImplementedError
def iterator(self, prefix=b'', reverse=False):
'''Return an iterator that yields (key, value) pairs from the
database sorted by key.
If `prefix` is set, only keys starting with `prefix` will be
included. If `reverse` is True the items are returned in
reverse order.
'''
raise NotImplementedError
class LevelDB(Storage):
'''LevelDB database engine.'''
@classmethod
def import_module(cls):
import plyvel
cls.module = plyvel
def open(self, name, create):
mof = 512 if self.for_sync else 128
# Use snappy compression (the default)
self.db = self.module.DB(name, create_if_missing=create,
max_open_files=mof)
self.close = self.db.close
self.get = self.db.get
self.put = self.db.put
self.iterator = self.db.iterator
self.write_batch = partial(self.db.write_batch, transaction=True,
sync=True)
class RocksDB(Storage):
'''RocksDB database engine.'''
@classmethod
def import_module(cls):
import rocksdb
cls.module = rocksdb
def open(self, name, create):
mof = 512 if self.for_sync else 128
# Use snappy compression (the default)
options = self.module.Options(create_if_missing=create,
use_fsync=True,
target_file_size_base=33554432,
max_open_files=mof)
self.db = self.module.DB(name, options)
self.get = self.db.get
self.put = self.db.put
def close(self):
# PyRocksDB doesn't provide a close method; hopefully this is enough
self.db = self.get = self.put = None
import gc
gc.collect()
def write_batch(self):
return RocksDBWriteBatch(self.db)
def iterator(self, prefix=b'', reverse=False):
return RocksDBIterator(self.db, prefix, reverse)
class RocksDBWriteBatch(object):
'''A write batch for RocksDB.'''
def __init__(self, db):
self.batch = RocksDB.module.WriteBatch()
self.db = db
def __enter__(self):
return self.batch
def __exit__(self, exc_type, exc_val, exc_tb):
if not exc_val:
self.db.write(self.batch)
class RocksDBIterator(object):
'''An iterator for RocksDB.'''
def __init__(self, db, prefix, reverse):
self.prefix = prefix
if reverse:
self.iterator = reversed(db.iteritems())
nxt_prefix = util.increment_byte_string(prefix)
if nxt_prefix:
self.iterator.seek(nxt_prefix)
try:
next(self.iterator)
except StopIteration:
self.iterator.seek(nxt_prefix)
else:
self.iterator.seek_to_last()
else:
self.iterator = db.iteritems()
self.iterator.seek(prefix)
def __iter__(self):
return self
def __next__(self):
k, v = next(self.iterator)
if not k.startswith(self.prefix):
raise StopIteration
return k, v