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