Rework the DB API a bit

lib/coins.py

@@ -19,6 +19,7 @@ import sys
 from lib.hash import Base58, hash160, double_sha256, hash_to_str
 from lib.script import ScriptPubKey
 from lib.tx import Deserializer
+from lib.util import subclasses
 
 
 class CoinError(Exception):
@@ -34,21 +35,12 @@ class Coin(object):
     VALUE_PER_COIN = 100000000
     CHUNK_SIZE=2016
 
-    @staticmethod
-    def coin_classes():
-        '''Return a list of coin classes in declaration order.'''
-        is_coin = lambda obj: (inspect.isclass(obj)
-                               and issubclass(obj, Coin)
-                               and obj != Coin)
-        pairs = inspect.getmembers(sys.modules[__name__], is_coin)
-        return [pair[1] for pair in pairs]
-
     @classmethod
     def lookup_coin_class(cls, name, net):
         '''Return a coin class given name and network.
 
         Raise an exception if unrecognised.'''
-        for coin in cls.coin_classes():
+        for coin in subclasses(Coin):
             if (coin.NAME.lower() == name.lower()
                     and coin.NET.lower() == net.lower()):
                 return coin

lib/util.py

@@ -9,6 +9,7 @@
 
 
 import array
+import inspect
 import logging
 import sys
 from collections import Container, Mapping
@@ -77,6 +78,14 @@ def deep_getsizeof(obj):
 
     return size(obj)
 
+def subclasses(base_class, strict=True):
+    '''Return a list of subclasses of base_class in its module.'''
+    def select(obj):
+        return (inspect.isclass(obj) and issubclass(obj, base_class)
+                and (not strict or obj != base_class))
+
+    pairs = inspect.getmembers(sys.modules[base_class.__module__], select)
+    return [pair[1] for pair in pairs]
 
 def chunks(items, size):
     '''Break up items, an iterable, into chunks of length size.'''

server/block_processor.py

@@ -22,7 +22,7 @@ from server.daemon import DaemonError
 from lib.hash import hash_to_str
 from lib.script import ScriptPubKey
 from lib.util import chunks, LoggedClass
-from server.storage import LMDB, RocksDB, LevelDB, NoDatabaseException
+from server.storage import open_db
 
 
 def formatted_time(t):
@@ -161,17 +161,17 @@ class BlockProcessor(LoggedClass):
         self.coin = env.coin
         self.reorg_limit = env.reorg_limit
 
-        # Chain state (initialize to genesis in case of new DB)
-        self.db_height = -1
-        self.db_tx_count = 0
-        self.db_tip = b'\0' * 32
-        self.flush_count = 0
-        self.utxo_flush_count = 0
-        self.wall_time = 0
-        self.first_sync = True
-
         # Open DB and metadata files.  Record some of its state.
-        self.db = self.open_db(self.coin, env.db_engine)
+        db_name = '{}-{}'.format(self.coin.NAME, self.coin.NET)
+        self.db = open_db(db_name, env.db_engine)
+        if self.db.is_new:
+            self.logger.info('created new {} database {}'
+                             .format(env.db_engine, db_name))
+        else:
+            self.logger.info('successfully opened {} database {}'
+                             .format(env.db_engine, db_name))
+
+        self.init_state()
         self.tx_count = self.db_tx_count
         self.height = self.db_height
         self.tip = self.db_tip
@@ -313,28 +313,17 @@ class BlockProcessor(LoggedClass):
 
         return self.fs_cache.block_hashes(start, count)
 
-    def open_db(self, coin, db_engine):
-        db_name = '{}-{}'.format(coin.NAME, coin.NET)
-        db_engine_class = {
-            "leveldb": LevelDB,
-            "rocksdb": RocksDB,
-            "lmdb": LMDB
-        }[db_engine.lower()]
-        try:
-            db = db_engine_class(db_name, create_if_missing=False,
-                                 error_if_exists=False, compression=None)
-        except NoDatabaseException:
-            db = db_engine_class(db_name, create_if_missing=True,
-                                 error_if_exists=True, compression=None)
-            self.logger.info('created new {} database {}'.format(db_engine, db_name))
+    def init_state(self):
+        if self.db.is_new:
+            self.db_height = -1
+            self.db_tx_count = 0
+            self.db_tip = b'\0' * 32
+            self.flush_count = 0
+            self.utxo_flush_count = 0
+            self.wall_time = 0
+            self.first_sync = True
         else:
-            self.logger.info('successfully opened {} database {}'.format(db_engine, db_name))
-            self.read_state(db)
-
-        return db
-
-    def read_state(self, db):
-        state = db.get(b'state')
+            state = self.db.get(b'state')
             state = ast.literal_eval(state.decode())
             if state['genesis'] != self.coin.GENESIS_HASH:
                 raise ChainError('DB genesis hash {} does not match coin {}'

server/storage.py

@@ -1,43 +1,83 @@
+# Copyright (c) 2016, the ElectrumX authors
+#
+# All rights reserved.
+#
+# See the file "LICENCE" for information about the copyright
+# and warranty status of this software.
+
+'''Backend database abstraction.
+
+The abstraction needs to be improved to not heavily penalise LMDB.
+'''
+
 import os
 from functools import partial
 
+from lib.util import subclasses
+
+
+def open_db(name, db_engine):
+    '''Returns a database handle.'''
+    for db_class in subclasses(Storage):
+        if db_class.__name__.lower() == db_engine.lower():
+            db_class.import_module()
+            return db_class(name)
+
+    raise RuntimeError('unrecognised DB engine "{}"'.format(db_engine))
+
 
 class Storage(object):
-    def __init__(self, name, create_if_missing=False, error_if_exists=False, compression=None):
-        if not create_if_missing and not os.path.exists(name):
-            raise NoDatabaseException
+    '''Abstract base class of the DB backend abstraction.'''
+
+    def __init__(self, name):
+        self.is_new = not os.path.exists(name)
+        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 get(self, key):
-        raise NotImplementedError()
+        raise NotImplementedError
 
     def put(self, key, value):
-        raise NotImplementedError()
+        raise NotImplementedError
 
     def write_batch(self):
-        """
-        Returns a context manager that provides `put` and `delete`.
-        Changes should only be committed when the context manager closes without an exception.
-        """
-        raise NotImplementedError()
+        '''Return a context manager that provides `put` and `delete`.
 
-    def iterator(self, prefix=b'', reverse=False):
-        """
-        Returns 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.
-        """
-        raise NotImplementedError()
+        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.
 
-class NoDatabaseException(Exception):
-    pass
+        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):
-    def __init__(self, name, create_if_missing=False, error_if_exists=False, compression=None):
-        super().__init__(name, create_if_missing, error_if_exists, compression)
+    '''LevelDB database engine.'''
+
+    @classmethod
+    def import_module(cls):
         import plyvel
-        self.db = plyvel.DB(name, create_if_missing=create_if_missing,
-                            error_if_exists=error_if_exists, compression=compression)
+        cls.module = plyvel
+
+    def open(self, name, create):
+        self.db = self.module.DB(name, create_if_missing=create,
+                                 compression=None)
         self.get = self.db.get
         self.put = self.db.put
         self.iterator = self.db.iterator
@@ -45,25 +85,28 @@ class LevelDB(Storage):
 
 
 class RocksDB(Storage):
-    rocksdb = None
+    '''RocksDB database engine.'''
 
-    def __init__(self, name, create_if_missing=False, error_if_exists=False, compression=None):
-        super().__init__(name, create_if_missing, error_if_exists, compression)
+    @classmethod
+    def import_module(cls):
         import rocksdb
-        RocksDB.rocksdb = rocksdb
-        if not compression:
+        cls.module = rocksdb
+
+    def open(self, name, create):
         compression = "no"
-        compression = getattr(rocksdb.CompressionType, compression + "_compression")
-        self.db = rocksdb.DB(name, rocksdb.Options(create_if_missing=create_if_missing,
+        compression = getattr(self.module.CompressionType,
+                              compression + "_compression")
+        options = self.module.Options(create_if_missing=create,
                                       compression=compression,
                                       target_file_size_base=33554432,
-                                                   max_open_files=1024))
+                                      max_open_files=1024)
+        self.db = self.module.DB(name, options)
         self.get = self.db.get
         self.put = self.db.put
 
     class WriteBatch(object):
         def __init__(self, db):
-            self.batch = RocksDB.rocksdb.WriteBatch()
+            self.batch = RocksDB.module.WriteBatch()
             self.db = db
 
         def __enter__(self):
@@ -99,14 +142,17 @@ class RocksDB(Storage):
 
 
 class LMDB(Storage):
-    lmdb = None
+    '''RocksDB database engine.'''
 
-    def __init__(self, name, create_if_missing=False, error_if_exists=False, compression=None):
-        super().__init__(name, create_if_missing, error_if_exists, compression)
+    @classmethod
+    def import_module(cls):
         import lmdb
-        LMDB.lmdb = lmdb
-        self.env = lmdb.Environment(".", subdir=True, create=create_if_missing, max_dbs=32, map_size=5 * 10 ** 10)
-        self.db = self.env.open_db(create=create_if_missing)
+        cls.module = lmdb
+
+    def open(self, name, create):
+        self.env = cls.module.Environment('.', subdir=True, create=create,
+                                          max_dbs=32, map_size=5 * 10 ** 10)
+        self.db = self.env.open_db(create=create)
 
     def get(self, key):
         with self.env.begin(db=self.db) as tx: