consolidate flush_backup

-move methods from History to LevelDB

lbry/wallet/server/block_processor.py

@@ -1,17 +1,22 @@
 import time
 import asyncio
+import typing
 from struct import pack, unpack
 from concurrent.futures.thread import ThreadPoolExecutor
-from typing import Optional
+from typing import Optional, List, Tuple
 from prometheus_client import Gauge, Histogram
 import lbry
 from lbry.schema.claim import Claim
+from lbry.wallet.server.tx import Tx
 from lbry.wallet.server.db.writer import SQLDB
 from lbry.wallet.server.daemon import DaemonError
 from lbry.wallet.server.hash import hash_to_hex_str, HASHX_LEN
 from lbry.wallet.server.util import chunks, class_logger
 from lbry.wallet.server.leveldb import FlushData
+from lbry.wallet.transaction import Transaction
 from lbry.wallet.server.udp import StatusServer
+if typing.TYPE_CHECKING:
+    from lbry.wallet.server.leveldb import LevelDB
 
 
 class Prefetcher:
@@ -153,7 +158,7 @@ class BlockProcessor:
         "reorg_count", "Number of reorgs", namespace=NAMESPACE
     )
 
-    def __init__(self, env, db, daemon, notifications):
+    def __init__(self, env, db: 'LevelDB', daemon, notifications):
         self.env = env
         self.db = db
         self.daemon = daemon
@@ -213,13 +218,10 @@ class BlockProcessor:
         chain = [self.tip] + [self.coin.header_hash(h) for h in headers[:-1]]
 
         if hprevs == chain:
+
             start = time.perf_counter()
             await self.run_in_thread_with_lock(self.advance_blocks, blocks)
-            for cache in self.search_cache.values():
-                cache.clear()
-            self.history_cache.clear()
-            self.notifications.notified_mempool_txs.clear()
-            await self._maybe_flush()
+
             processed_time = time.perf_counter() - start
             self.block_count_metric.set(self.height)
             self.block_update_time_metric.observe(processed_time)
@@ -252,7 +254,6 @@ class BlockProcessor:
         else:
             self.logger.info(f'faking a reorg of {count:,d} blocks')
 
-
         async def get_raw_blocks(last_height, hex_hashes):
             heights = range(last_height, last_height - len(hex_hashes), -1)
             try:
@@ -262,24 +263,17 @@ class BlockProcessor:
             except FileNotFoundError:
                 return await self.daemon.raw_blocks(hex_hashes)
 
-        def flush_backup():
-            # self.touched can include other addresses which is
-            # harmless, but remove None.
-            self.touched.discard(None)
-            self.db.flush_backup(self.flush_data(), self.touched)
-
         try:
             await self.flush(True)
-
             start, last, hashes = await self.reorg_hashes(count)
             # Reverse and convert to hex strings.
             hashes = [hash_to_hex_str(hash) for hash in reversed(hashes)]
             self.logger.info("reorg %i block hashes", len(hashes))
+
             for hex_hashes in chunks(hashes, 50):
                 raw_blocks = await get_raw_blocks(last, hex_hashes)
                 self.logger.info("got %i raw blocks", len(raw_blocks))
                 await self.run_in_thread_with_lock(self.backup_blocks, raw_blocks)
-                await self.run_in_thread_with_lock(flush_backup)
                 last -= len(raw_blocks)
 
             await self.run_in_thread_with_lock(self.db.sql.delete_claims_above_height, self.height)
@@ -358,8 +352,7 @@ class BlockProcessor:
 
     async def flush(self, flush_utxos):
         def flush():
-            self.db.flush_dbs(self.flush_data(), flush_utxos,
-                              self.estimate_txs_remaining)
+            self.db.flush_dbs(self.flush_data(), self.estimate_txs_remaining)
         await self.run_in_thread_with_lock(flush)
 
     async def _maybe_flush(self):
@@ -378,7 +371,7 @@ class BlockProcessor:
         one_MB = 1000*1000
         utxo_cache_size = len(self.utxo_cache) * 205
         db_deletes_size = len(self.db_deletes) * 57
-        hist_cache_size = self.db.history.unflushed_memsize()
+        hist_cache_size = len(self.db.hist_unflushed) * 180 + self.db.hist_unflushed_count * 4
         # Roughly ntxs * 32 + nblocks * 42
         tx_hash_size = ((self.tx_count - self.db.fs_tx_count) * 32
                         + (self.height - self.db.fs_height) * 42)
@@ -420,13 +413,20 @@ class BlockProcessor:
         self.headers.extend(headers)
         self.tip = self.coin.header_hash(headers[-1])
 
-    def advance_txs(self, height, txs, header, block_hash):
+        self.db.flush_dbs(self.flush_data(), self.estimate_txs_remaining)
+
+        for cache in self.search_cache.values():
+            cache.clear()
+        self.history_cache.clear()
+        self.notifications.notified_mempool_txs.clear()
+
+    def advance_txs(self, height, txs: List[Tuple[Tx, bytes]], header, block_hash):
         self.block_hashes.append(block_hash)
         self.block_txs.append((b''.join(tx_hash for tx, tx_hash in txs), [tx.raw for tx, _ in txs]))
 
         undo_info = []
-        tx_num = self.tx_count
         hashXs_by_tx = []
+        tx_num = self.tx_count
 
         # Use local vars for speed in the loops
         put_utxo = self.utxo_cache.__setitem__
@@ -462,7 +462,15 @@ class BlockProcessor:
             self.db.total_transactions.append(tx_hash)
             tx_num += 1
 
-        self.db.history.add_unflushed(hashXs_by_tx, self.tx_count)
+        # self.db.add_unflushed(hashXs_by_tx, self.tx_count)
+        first_tx_num = self.tx_count
+        _unflushed = self.db.hist_unflushed
+        _count = 0
+        for _tx_num, _hashXs in enumerate(hashXs_by_tx, start=first_tx_num):
+            for _hashX in set(_hashXs):
+                _unflushed[_hashX].append(_tx_num)
+            _count += len(_hashXs)
+        self.db.hist_unflushed_count += _count
         self.tx_count = tx_num
         self.db.tx_counts.append(tx_num)
 
@@ -493,6 +501,10 @@ class BlockProcessor:
             self.height -= 1
             self.db.tx_counts.pop()
 
+        # self.touched can include other addresses which is
+        # harmless, but remove None.
+        self.touched.discard(None)
+        self.db.flush_backup(self.flush_data(), self.touched)
         self.logger.info(f'backed up to height {self.height:,d}')
 
     def backup_txs(self, txs):
@@ -603,11 +615,11 @@ class BlockProcessor:
         # Value: hashX
         prefix = b'h' + tx_hash[:4] + idx_packed
         candidates = {db_key: hashX for db_key, hashX
-                      in self.db.utxo_db.iterator(prefix=prefix)}
+                      in self.db.db.iterator(prefix=prefix)}
+
         for hdb_key, hashX in candidates.items():
             tx_num_packed = hdb_key[-4:]
             if len(candidates) > 1:
-
                 tx_num, = unpack('<I', tx_num_packed)
                 try:
                     hash, height = self.db.fs_tx_hash(tx_num)
@@ -622,7 +634,7 @@ class BlockProcessor:
             # Key: b'u' + address_hashX + tx_idx + tx_num
             # Value: the UTXO value as a 64-bit unsigned integer
             udb_key = b'u' + hashX + hdb_key[-6:]
-            utxo_value_packed = self.db.utxo_db.get(udb_key)
+            utxo_value_packed = self.db.db.get(udb_key)
             if utxo_value_packed is None:
                 self.logger.warning(
                     "%s:%s is not found in UTXO db for %s", hash_to_hex_str(tx_hash), tx_idx, hash_to_hex_str(hashX)
@@ -631,6 +643,7 @@ class BlockProcessor:
             # Remove both entries for this UTXO
             self.db_deletes.append(hdb_key)
             self.db_deletes.append(udb_key)
+
             return hashX + tx_num_packed + utxo_value_packed
 
         self.logger.error('UTXO {hash_to_hex_str(tx_hash)} / {tx_idx} not found in "h" table')

lbry/wallet/server/history.py

@@ -1,324 +0,0 @@
-# Copyright (c) 2016-2018, Neil Booth
-# Copyright (c) 2017, the ElectrumX authors
-#
-# All rights reserved.
-#
-# See the file "LICENCE" for information about the copyright
-# and warranty status of this software.
-
-"""History by script hash (address)."""
-
-import array
-import ast
-import bisect
-import time
-from collections import defaultdict
-from functools import partial
-
-from lbry.wallet.server import util
-from lbry.wallet.server.util import pack_be_uint16, unpack_be_uint16_from
-from lbry.wallet.server.hash import hash_to_hex_str, HASHX_LEN
-
-
-class History:
-
-    DB_VERSIONS = [0]
-
-    def __init__(self):
-        self.logger = util.class_logger(__name__, self.__class__.__name__)
-        # For history compaction
-        self.max_hist_row_entries = 12500
-        self.unflushed = defaultdict(partial(array.array, 'I'))
-        self.unflushed_count = 0
-        self.db = None
-
-    def open_db(self, db_class, for_sync, utxo_flush_count, compacting):
-        self.db = db_class('hist', for_sync)
-        self.read_state()
-        self.clear_excess(utxo_flush_count)
-        # An incomplete compaction needs to be cancelled otherwise
-        # restarting it will corrupt the history
-        if not compacting:
-            self._cancel_compaction()
-        return self.flush_count
-
-    def close_db(self):
-        if self.db:
-            self.db.close()
-            self.db = None
-
-    def read_state(self):
-        state = self.db.get(b'state\0\0')
-        if state:
-            state = ast.literal_eval(state.decode())
-            if not isinstance(state, dict):
-                raise RuntimeError('failed reading state from history DB')
-            self.flush_count = state['flush_count']
-            self.comp_flush_count = state.get('comp_flush_count', -1)
-            self.comp_cursor = state.get('comp_cursor', -1)
-            self.db_version = state.get('db_version', 0)
-        else:
-            self.flush_count = 0
-            self.comp_flush_count = -1
-            self.comp_cursor = -1
-            self.db_version = max(self.DB_VERSIONS)
-
-        self.logger.info(f'history DB version: {self.db_version}')
-        if self.db_version not in self.DB_VERSIONS:
-            msg = f'this software only handles DB versions {self.DB_VERSIONS}'
-            self.logger.error(msg)
-            raise RuntimeError(msg)
-        self.logger.info(f'flush count: {self.flush_count:,d}')
-
-    def clear_excess(self, utxo_flush_count):
-        # < might happen at end of compaction as both DBs cannot be
-        # updated atomically
-        if self.flush_count <= utxo_flush_count:
-            return
-
-        self.logger.info('DB shut down uncleanly.  Scanning for '
-                         'excess history flushes...')
-
-        keys = []
-        for key, hist in self.db.iterator(prefix=b''):
-            flush_id, = unpack_be_uint16_from(key[-2:])
-            if flush_id > utxo_flush_count:
-                keys.append(key)
-
-        self.logger.info(f'deleting {len(keys):,d} history entries')
-
-        self.flush_count = utxo_flush_count
-        with self.db.write_batch() as batch:
-            for key in keys:
-                batch.delete(key)
-            self.write_state(batch)
-
-        self.logger.info('deleted excess history entries')
-
-    def write_state(self, batch):
-        """Write state to the history DB."""
-        state = {
-            'flush_count': self.flush_count,
-            'comp_flush_count': self.comp_flush_count,
-            'comp_cursor': self.comp_cursor,
-            'db_version': self.db_version,
-        }
-        # History entries are not prefixed; the suffix \0\0 ensures we
-        # look similar to other entries and aren't interfered with
-        batch.put(b'state\0\0', repr(state).encode())
-
-    def add_unflushed(self, hashXs_by_tx, first_tx_num):
-        unflushed = self.unflushed
-        count = 0
-        for tx_num, hashXs in enumerate(hashXs_by_tx, start=first_tx_num):
-            hashXs = set(hashXs)
-            for hashX in hashXs:
-                unflushed[hashX].append(tx_num)
-            count += len(hashXs)
-        self.unflushed_count += count
-
-    def unflushed_memsize(self):
-        return len(self.unflushed) * 180 + self.unflushed_count * 4
-
-    def assert_flushed(self):
-        assert not self.unflushed
-
-    def flush(self):
-        start_time = time.time()
-        self.flush_count += 1
-        flush_id = pack_be_uint16(self.flush_count)
-        unflushed = self.unflushed
-
-        with self.db.write_batch() as batch:
-            for hashX in sorted(unflushed):
-                key = hashX + flush_id
-                batch.put(key, unflushed[hashX].tobytes())
-            self.write_state(batch)
-
-        count = len(unflushed)
-        unflushed.clear()
-        self.unflushed_count = 0
-
-        if self.db.for_sync:
-            elapsed = time.time() - start_time
-            self.logger.info(f'flushed history in {elapsed:.1f}s '
-                             f'for {count:,d} addrs')
-
-    def backup(self, hashXs, tx_count):
-        # Not certain this is needed, but it doesn't hurt
-        self.flush_count += 1
-        nremoves = 0
-        bisect_left = bisect.bisect_left
-
-        with self.db.write_batch() as batch:
-            for hashX in sorted(hashXs):
-                deletes = []
-                puts = {}
-                for key, hist in self.db.iterator(prefix=hashX, reverse=True):
-                    a = array.array('I')
-                    a.frombytes(hist)
-                    # Remove all history entries >= tx_count
-                    idx = bisect_left(a, tx_count)
-                    nremoves += len(a) - idx
-                    if idx > 0:
-                        puts[key] = a[:idx].tobytes()
-                        break
-                    deletes.append(key)
-
-                for key in deletes:
-                    batch.delete(key)
-                for key, value in puts.items():
-                    batch.put(key, value)
-            self.write_state(batch)
-
-        self.logger.info(f'backing up removed {nremoves:,d} history entries')
-
-    # def get_txnums(self, hashX, limit=1000):
-    #     """Generator that returns an unpruned, sorted list of tx_nums in the
-    #     history of a hashX.  Includes both spending and receiving
-    #     transactions.  By default yields at most 1000 entries.  Set
-    #     limit to None to get them all.  """
-    #     limit = util.resolve_limit(limit)
-    #     for key, hist in self.db.iterator(prefix=hashX):
-    #         a = array.array('I')
-    #         a.frombytes(hist)
-    #         for tx_num in a:
-    #             if limit == 0:
-    #                 return
-    #             yield tx_num
-    #             limit -= 1
-
-    #
-    # History compaction
-    #
-
-    # comp_cursor is a cursor into compaction progress.
-    # -1: no compaction in progress
-    # 0-65535: Compaction in progress; all prefixes < comp_cursor have
-    #     been compacted, and later ones have not.
-    # 65536: compaction complete in-memory but not flushed
-    #
-    # comp_flush_count applies during compaction, and is a flush count
-    #     for history with prefix < comp_cursor.  flush_count applies
-    #     to still uncompacted history.  It is -1 when no compaction is
-    #     taking place.  Key suffixes up to and including comp_flush_count
-    #     are used, so a parallel history flush must first increment this
-    #
-    # When compaction is complete and the final flush takes place,
-    # flush_count is reset to comp_flush_count, and comp_flush_count to -1
-
-    def _flush_compaction(self, cursor, write_items, keys_to_delete):
-        """Flush a single compaction pass as a batch."""
-        # Update compaction state
-        if cursor == 65536:
-            self.flush_count = self.comp_flush_count
-            self.comp_cursor = -1
-            self.comp_flush_count = -1
-        else:
-            self.comp_cursor = cursor
-
-        # History DB.  Flush compacted history and updated state
-        with self.db.write_batch() as batch:
-            # Important: delete first!  The keyspace may overlap.
-            for key in keys_to_delete:
-                batch.delete(key)
-            for key, value in write_items:
-                batch.put(key, value)
-            self.write_state(batch)
-
-    def _compact_hashX(self, hashX, hist_map, hist_list,
-                       write_items, keys_to_delete):
-        """Compress history for a hashX.  hist_list is an ordered list of
-        the histories to be compressed."""
-        # History entries (tx numbers) are 4 bytes each.  Distribute
-        # over rows of up to 50KB in size.  A fixed row size means
-        # future compactions will not need to update the first N - 1
-        # rows.
-        max_row_size = self.max_hist_row_entries * 4
-        full_hist = b''.join(hist_list)
-        nrows = (len(full_hist) + max_row_size - 1) // max_row_size
-        if nrows > 4:
-            self.logger.info('hashX {} is large: {:,d} entries across '
-                             '{:,d} rows'
-                             .format(hash_to_hex_str(hashX),
-                                     len(full_hist) // 4, nrows))
-
-        # Find what history needs to be written, and what keys need to
-        # be deleted.  Start by assuming all keys are to be deleted,
-        # and then remove those that are the same on-disk as when
-        # compacted.
-        write_size = 0
-        keys_to_delete.update(hist_map)
-        for n, chunk in enumerate(util.chunks(full_hist, max_row_size)):
-            key = hashX + pack_be_uint16(n)
-            if hist_map.get(key) == chunk:
-                keys_to_delete.remove(key)
-            else:
-                write_items.append((key, chunk))
-                write_size += len(chunk)
-
-        assert n + 1 == nrows
-        self.comp_flush_count = max(self.comp_flush_count, n)
-
-        return write_size
-
-    def _compact_prefix(self, prefix, write_items, keys_to_delete):
-        """Compact all history entries for hashXs beginning with the
-        given prefix.  Update keys_to_delete and write."""
-        prior_hashX = None
-        hist_map = {}
-        hist_list = []
-
-        key_len = HASHX_LEN + 2
-        write_size = 0
-        for key, hist in self.db.iterator(prefix=prefix):
-            # Ignore non-history entries
-            if len(key) != key_len:
-                continue
-            hashX = key[:-2]
-            if hashX != prior_hashX and prior_hashX:
-                write_size += self._compact_hashX(prior_hashX, hist_map,
-                                                  hist_list, write_items,
-                                                  keys_to_delete)
-                hist_map.clear()
-                hist_list.clear()
-            prior_hashX = hashX
-            hist_map[key] = hist
-            hist_list.append(hist)
-
-        if prior_hashX:
-            write_size += self._compact_hashX(prior_hashX, hist_map, hist_list,
-                                              write_items, keys_to_delete)
-        return write_size
-
-    def _compact_history(self, limit):
-        """Inner loop of history compaction.  Loops until limit bytes have
-        been processed.
-        """
-        keys_to_delete = set()
-        write_items = []   # A list of (key, value) pairs
-        write_size = 0
-
-        # Loop over 2-byte prefixes
-        cursor = self.comp_cursor
-        while write_size < limit and cursor < 65536:
-            prefix = pack_be_uint16(cursor)
-            write_size += self._compact_prefix(prefix, write_items,
-                                               keys_to_delete)
-            cursor += 1
-
-        max_rows = self.comp_flush_count + 1
-        self._flush_compaction(cursor, write_items, keys_to_delete)
-
-        self.logger.info('history compaction: wrote {:,d} rows ({:.1f} MB), '
-                         'removed {:,d} rows, largest: {:,d}, {:.1f}% complete'
-                         .format(len(write_items), write_size / 1000000,
-                                 len(keys_to_delete), max_rows,
-                                 100 * cursor / 65536))
-        return write_size
-
-    def _cancel_compaction(self):
-        if self.comp_cursor != -1:
-            self.logger.warning('cancelling in-progress history compaction')
-            self.comp_flush_count = -1
-            self.comp_cursor = -1

lbry/wallet/server/leveldb.py

@@ -17,9 +17,10 @@ import time
 import zlib
 import typing
 from typing import Optional, List, Tuple, Iterable
+from functools import partial
 from asyncio import sleep
-from bisect import bisect_right
-from collections import namedtuple
+from bisect import bisect_right, bisect_left
+from collections import namedtuple, defaultdict
 from glob import glob
 from struct import pack, unpack
 from concurrent.futures.thread import ThreadPoolExecutor
@@ -28,19 +29,25 @@ from lbry.utils import LRUCacheWithMetrics
 from lbry.wallet.server import util
 from lbry.wallet.server.hash import hash_to_hex_str, HASHX_LEN
 from lbry.wallet.server.merkle import Merkle, MerkleCache
-from lbry.wallet.server.util import formatted_time
+from lbry.wallet.server.util import formatted_time, pack_be_uint16, unpack_be_uint16_from
 from lbry.wallet.server.storage import db_class
-from lbry.wallet.server.history import History
 
 
 UTXO = namedtuple("UTXO", "tx_num tx_pos tx_hash height value")
-HEADER_PREFIX = b'H'
-TX_COUNT_PREFIX = b'T'
-TX_HASH_PREFIX = b'X'
+HISTORY_PREFIX = b'A'
 TX_PREFIX = b'B'
-TX_NUM_PREFIX = b'N'
 BLOCK_HASH_PREFIX = b'C'
+HEADER_PREFIX = b'H'
+TX_NUM_PREFIX = b'N'
+TX_COUNT_PREFIX = b'T'
+UNDO_PREFIX = b'U'
+TX_HASH_PREFIX = b'X'
 
+HASHX_UTXO_PREFIX = b'h'
+HIST_STATE = b'state-hist'
+UTXO_STATE = b'state-utxo'
+UTXO_PREFIX = b'u'
+HASHX_HISTORY_PREFIX = b'x'
 
 
 @attr.s(slots=True)
@@ -65,6 +72,7 @@ class LevelDB:
     """
 
     DB_VERSIONS = [6]
+    HIST_DB_VERSIONS = [0]
 
     class DBError(Exception):
         """Raised on general DB errors generally indicating corruption."""
@@ -78,8 +86,14 @@ class LevelDB:
         self.logger.info(f'switching current directory to {env.db_dir}')
 
         self.db_class = db_class(env.db_dir, self.env.db_engine)
-        self.history = History()
-        self.utxo_db = None
+        self.db = None
+
+        self.hist_unflushed = defaultdict(partial(array.array, 'I'))
+        self.hist_unflushed_count = 0
+        self.hist_flush_count = 0
+        self.hist_comp_flush_count = -1
+        self.hist_comp_cursor = -1
+
         self.tx_counts = None
         self.headers = None
         self.last_flush = time.time()
@@ -96,6 +110,19 @@ class LevelDB:
         self._tx_and_merkle_cache = LRUCacheWithMetrics(2 ** 17, metric_name='tx_and_merkle', namespace="wallet_server")
         self.total_transactions = None
 
+    # def add_unflushed(self, hashXs_by_tx, first_tx_num):
+    #     unflushed = self.history.unflushed
+    #     count = 0
+    #     for tx_num, hashXs in enumerate(hashXs_by_tx, start=first_tx_num):
+    #         hashXs = set(hashXs)
+    #         for hashX in hashXs:
+    #             unflushed[hashX].append(tx_num)
+    #         count += len(hashXs)
+    #     self.history.unflushed_count += count
+
+    # def unflushed_memsize(self):
+    #     return len(self.history.unflushed) * 180 + self.history.unflushed_count * 4
+
     async def _read_tx_counts(self):
         if self.tx_counts is not None:
             return
@@ -105,7 +132,7 @@ class LevelDB:
         def get_counts():
             return tuple(
                 util.unpack_be_uint64(tx_count)
-                for tx_count in self.tx_db.iterator(prefix=TX_COUNT_PREFIX, include_key=False)
+                for tx_count in self.db.iterator(prefix=TX_COUNT_PREFIX, include_key=False)
             )
 
         tx_counts = await asyncio.get_event_loop().run_in_executor(self.executor, get_counts)
@@ -120,7 +147,7 @@ class LevelDB:
 
     async def _read_txids(self):
         def get_txids():
-            return list(self.tx_db.iterator(prefix=TX_HASH_PREFIX, include_key=False))
+            return list(self.db.iterator(prefix=TX_HASH_PREFIX, include_key=False))
 
         start = time.perf_counter()
         self.logger.info("loading txids")
@@ -136,7 +163,7 @@ class LevelDB:
 
         def get_headers():
             return [
-                header for header in self.headers_db.iterator(prefix=HEADER_PREFIX, include_key=False)
+                header for header in self.db.iterator(prefix=HEADER_PREFIX, include_key=False)
             ]
 
         headers = await asyncio.get_event_loop().run_in_executor(self.executor, get_headers)
@@ -152,31 +179,97 @@ class LevelDB:
                 f.write(f'ElectrumX databases and metadata for '
                         f'{self.coin.NAME} {self.coin.NET}'.encode())
 
-        assert self.headers_db is None
-        self.headers_db = self.db_class('headers', for_sync)
-        if self.headers_db.is_new:
-            self.logger.info('created new headers db')
-        self.logger.info(f'opened headers DB (for sync: {for_sync})')
+        assert self.db is None
+        self.db = self.db_class(f'lbry-{self.env.db_engine}', for_sync)
+        if self.db.is_new:
+            self.logger.info('created new db: %s', f'lbry-{self.env.db_engine}')
+        self.logger.info(f'opened DB (for sync: {for_sync})')
 
-        assert self.tx_db is None
-        self.tx_db = self.db_class('tx', for_sync)
-        if self.tx_db.is_new:
-            self.logger.info('created new tx db')
-        self.logger.info(f'opened tx DB (for sync: {for_sync})')
-
-        assert self.utxo_db is None
-        # First UTXO DB
-        self.utxo_db = self.db_class('utxo', for_sync)
-        if self.utxo_db.is_new:
-            self.logger.info('created new utxo db')
-        self.logger.info(f'opened utxo db (for sync: {for_sync})')
         self.read_utxo_state()
 
         # Then history DB
-        self.utxo_flush_count = self.history.open_db(
-            self.db_class, for_sync, self.utxo_flush_count, compacting
-        )
-        self.clear_excess_undo_info()
+        state = self.db.get(HIST_STATE)
+        if state:
+            state = ast.literal_eval(state.decode())
+            if not isinstance(state, dict):
+                raise RuntimeError('failed reading state from history DB')
+            self.hist_flush_count = state['flush_count']
+            self.hist_comp_flush_count = state.get('comp_flush_count', -1)
+            self.hist_comp_cursor = state.get('comp_cursor', -1)
+            self.hist_db_version = state.get('db_version', 0)
+        else:
+            self.hist_flush_count = 0
+            self.hist_comp_flush_count = -1
+            self.hist_comp_cursor = -1
+            self.hist_db_version = max(self.HIST_DB_VERSIONS)
+
+        self.logger.info(f'history DB version: {self.hist_db_version}')
+        if self.hist_db_version not in self.HIST_DB_VERSIONS:
+            msg = f'this software only handles DB versions {self.HIST_DB_VERSIONS}'
+            self.logger.error(msg)
+            raise RuntimeError(msg)
+        self.logger.info(f'flush count: {self.hist_flush_count:,d}')
+
+        # self.history.clear_excess(self.utxo_flush_count)
+        # < might happen at end of compaction as both DBs cannot be
+        # updated atomically
+        if self.hist_flush_count > self.utxo_flush_count:
+            self.logger.info('DB shut down uncleanly.  Scanning for '
+                             'excess history flushes...')
+
+            keys = []
+            for key, hist in self.db.iterator(prefix=HASHX_HISTORY_PREFIX):
+                k = key[1:]
+                flush_id, = unpack_be_uint16_from(k[-2:])
+                if flush_id > self.utxo_flush_count:
+                    keys.append(k)
+
+            self.logger.info(f'deleting {len(keys):,d} history entries')
+
+            self.hist_flush_count = self.utxo_flush_count
+            with self.db.write_batch() as batch:
+                for key in keys:
+                    batch.delete(HASHX_HISTORY_PREFIX + key)
+                state = {
+                    'flush_count': self.hist_flush_count,
+                    'comp_flush_count': self.hist_comp_flush_count,
+                    'comp_cursor': self.hist_comp_cursor,
+                    'db_version': self.hist_db_version,
+                }
+                # History entries are not prefixed; the suffix \0\0 ensures we
+                # look similar to other entries and aren't interfered with
+                batch.put(HIST_STATE, repr(state).encode())
+
+            self.logger.info('deleted excess history entries')
+
+        self.utxo_flush_count = self.hist_flush_count
+
+        min_height = self.min_undo_height(self.db_height)
+        keys = []
+        for key, hist in self.db.iterator(prefix=UNDO_PREFIX):
+            height, = unpack('>I', key[-4:])
+            if height >= min_height:
+                break
+            keys.append(key)
+
+        if keys:
+            with self.db.write_batch() as batch:
+                for key in keys:
+                    batch.delete(key)
+            self.logger.info(f'deleted {len(keys):,d} stale undo entries')
+
+        # delete old block files
+        prefix = self.raw_block_prefix()
+        paths = [path for path in glob(f'{prefix}[0-9]*')
+                 if len(path) > len(prefix)
+                 and int(path[len(prefix):]) < min_height]
+        if paths:
+            for path in paths:
+                try:
+                    os.remove(path)
+                except FileNotFoundError:
+                    pass
+            self.logger.info(f'deleted {len(paths):,d} stale block files')
 
         # Read TX counts (requires meta directory)
         await self._read_tx_counts()
@@ -185,10 +278,7 @@ class LevelDB:
         await self._read_headers()
 
     def close(self):
-        self.utxo_db.close()
-        self.history.close_db()
-        self.headers_db.close()
-        self.tx_db.close()
+        self.db.close()
         self.executor.shutdown(wait=True)
         self.executor = None
 
@@ -209,18 +299,12 @@ class LevelDB:
         """Open the databases for serving.  If they are already open they are
         closed first.
         """
-        self.logger.info('closing DBs to re-open for serving')
-        if self.utxo_db:
-            self.logger.info('closing DBs to re-open for serving')
-            self.utxo_db.close()
-            self.history.close_db()
-            self.utxo_db = None
-        if self.headers_db:
-            self.headers_db.close()
-            self.headers_db = None
-        if self.tx_db:
-            self.tx_db.close()
-            self.tx_db = None
+        if self.db:
+            return
+            # self.logger.info('closing DBs to re-open for serving')
+            # self.db.close()
+            # self.history.close_db()
+            # self.db = None
 
         await self._open_dbs(False, False)
         self.logger.info("opened for serving")
@@ -249,107 +333,7 @@ class LevelDB:
         assert not flush_data.adds
         assert not flush_data.deletes
         assert not flush_data.undo_infos
-        self.history.assert_flushed()
-
-    def flush_dbs(self, flush_data, flush_utxos, estimate_txs_remaining):
-        """Flush out cached state.  History is always flushed; UTXOs are
-        flushed if flush_utxos."""
-        if flush_data.height == self.db_height:
-            self.assert_flushed(flush_data)
-            return
-
-        start_time = time.time()
-        prior_flush = self.last_flush
-        tx_delta = flush_data.tx_count - self.last_flush_tx_count
-
-        # Flush to file system
-        self.flush_fs(flush_data)
-
-        # Then history
-        self.flush_history()
-
-        # Flush state last as it reads the wall time.
-        with self.utxo_db.write_batch() as batch:
-            if flush_utxos:
-                self.flush_utxo_db(batch, flush_data)
-            self.flush_state(batch)
-
-        # Update and put the wall time again - otherwise we drop the
-        # time it took to commit the batch
-        self.flush_state(self.utxo_db)
-
-        elapsed = self.last_flush - start_time
-        self.logger.info(f'flush #{self.history.flush_count:,d} took '
-                         f'{elapsed:.1f}s.  Height {flush_data.height:,d} '
-                         f'txs: {flush_data.tx_count:,d} ({tx_delta:+,d})')
-
-        # Catch-up stats
-        if self.utxo_db.for_sync:
-            flush_interval = self.last_flush - prior_flush
-            tx_per_sec_gen = int(flush_data.tx_count / self.wall_time)
-            tx_per_sec_last = 1 + int(tx_delta / flush_interval)
-            eta = estimate_txs_remaining() / tx_per_sec_last
-            self.logger.info(f'tx/sec since genesis: {tx_per_sec_gen:,d}, '
-                             f'since last flush: {tx_per_sec_last:,d}')
-            self.logger.info(f'sync time: {formatted_time(self.wall_time)}  '
-                             f'ETA: {formatted_time(eta)}')
-
-    def flush_fs(self, flush_data):
-        """Write headers, tx counts and block tx hashes to the filesystem.
-
-        The first height to write is self.fs_height + 1.  The FS
-        metadata is all append-only, so in a crash we just pick up
-        again from the height stored in the DB.
-        """
-        prior_tx_count = (self.tx_counts[self.fs_height]
-                          if self.fs_height >= 0 else 0)
-        assert len(flush_data.block_txs) == len(flush_data.headers)
-        assert flush_data.height == self.fs_height + len(flush_data.headers)
-        assert flush_data.tx_count == (self.tx_counts[-1] if self.tx_counts
-                                       else 0)
-        assert len(self.tx_counts) == flush_data.height + 1
-        assert len(
-            b''.join(hashes for hashes, _ in flush_data.block_txs)
-        ) // 32 == flush_data.tx_count - prior_tx_count
-
-        # Write the headers
-        start_time = time.perf_counter()
-
-        with self.headers_db.write_batch() as batch:
-            batch_put = batch.put
-            for i, header in enumerate(flush_data.headers):
-                batch_put(HEADER_PREFIX + util.pack_be_uint64(self.fs_height + i + 1), header)
-                self.headers.append(header)
-        flush_data.headers.clear()
-
-        height_start = self.fs_height + 1
-        tx_num = prior_tx_count
-
-        with self.tx_db.write_batch() as batch:
-            batch_put = batch.put
-            for block_hash, (tx_hashes, txs) in zip(flush_data.block_hashes, flush_data.block_txs):
-                tx_count = self.tx_counts[height_start]
-                batch_put(BLOCK_HASH_PREFIX + util.pack_be_uint64(height_start), block_hash[::-1])
-                batch_put(TX_COUNT_PREFIX + util.pack_be_uint64(height_start), util.pack_be_uint64(tx_count))
-                height_start += 1
-                offset = 0
-                while offset < len(tx_hashes):
-                    batch_put(TX_HASH_PREFIX + util.pack_be_uint64(tx_num), tx_hashes[offset:offset+32])
-                    batch_put(TX_NUM_PREFIX + tx_hashes[offset:offset+32], util.pack_be_uint64(tx_num))
-                    batch_put(TX_PREFIX + tx_hashes[offset:offset+32], txs[offset // 32])
-                    tx_num += 1
-                    offset += 32
-
-        flush_data.block_txs.clear()
-        flush_data.block_hashes.clear()
-
-        self.fs_height = flush_data.height
-        self.fs_tx_count = flush_data.tx_count
-        elapsed = time.perf_counter() - start_time
-        self.logger.info(f'flushed filesystem data in {elapsed:.2f}s')
-
-    def flush_history(self):
-        self.history.flush()
+        assert not self.hist_unflushed
 
     def flush_utxo_db(self, batch, flush_data):
         """Flush the cached DB writes and UTXO set to the batch."""
@@ -372,15 +356,16 @@ class LevelDB:
             # suffix = tx_idx + tx_num
             hashX = value[:-12]
             suffix = key[-2:] + value[-12:-8]
-            batch_put(b'h' + key[:4] + suffix, hashX)
-            batch_put(b'u' + hashX + suffix, value[-8:])
+            batch_put(HASHX_UTXO_PREFIX + key[:4] + suffix, hashX)
+            batch_put(UTXO_PREFIX + hashX + suffix, value[-8:])
         flush_data.adds.clear()
 
         # New undo information
-        self.flush_undo_infos(batch_put, flush_data.undo_infos)
+        for undo_info, height in flush_data.undo_infos:
+            batch_put(self.undo_key(height), b''.join(undo_info))
         flush_data.undo_infos.clear()
 
-        if self.utxo_db.for_sync:
+        if self.db.for_sync:
             block_count = flush_data.height - self.db_height
             tx_count = flush_data.tx_count - self.db_tx_count
             elapsed = time.time() - start_time
@@ -389,49 +374,196 @@ class LevelDB:
                              f'{spend_count:,d} spends in '
                              f'{elapsed:.1f}s, committing...')
 
-        self.utxo_flush_count = self.history.flush_count
+        self.utxo_flush_count = self.hist_flush_count
         self.db_height = flush_data.height
         self.db_tx_count = flush_data.tx_count
         self.db_tip = flush_data.tip
 
-    def flush_state(self, batch):
-        """Flush chain state to the batch."""
+    def write_history_state(self, batch):
+        state = {
+            'flush_count': self.hist_flush_count,
+            'comp_flush_count': self.hist_comp_flush_count,
+            'comp_cursor': self.hist_comp_cursor,
+            'db_version': self.db_version,
+        }
+        # History entries are not prefixed; the suffix \0\0 ensures we
+        # look similar to other entries and aren't interfered with
+        batch.put(HIST_STATE, repr(state).encode())
+
+    def flush_dbs(self, flush_data: FlushData, estimate_txs_remaining):
+        """Flush out cached state.  History is always flushed; UTXOs are
+        flushed if flush_utxos."""
+        if flush_data.height == self.db_height:
+            self.assert_flushed(flush_data)
+            return
+
+        start_time = time.time()
+        prior_flush = self.last_flush
+        tx_delta = flush_data.tx_count - self.last_flush_tx_count
+
+        # Flush to file system
+        # self.flush_fs(flush_data)
+        prior_tx_count = (self.tx_counts[self.fs_height]
+                          if self.fs_height >= 0 else 0)
+
+        assert len(flush_data.block_txs) == len(flush_data.headers)
+        assert flush_data.height == self.fs_height + len(flush_data.headers)
+        assert flush_data.tx_count == (self.tx_counts[-1] if self.tx_counts
+                                       else 0)
+        assert len(self.tx_counts) == flush_data.height + 1
+        assert len(
+            b''.join(hashes for hashes, _ in flush_data.block_txs)
+        ) // 32 == flush_data.tx_count - prior_tx_count
+
+
+        # Write the headers
+        start_time = time.perf_counter()
+
+        with self.db.write_batch() as batch:
+            batch_put = batch.put
+            height_start = self.fs_height + 1
+            tx_num = prior_tx_count
+            for i, (header, block_hash, (tx_hashes, txs)) in enumerate(zip(flush_data.headers, flush_data.block_hashes, flush_data.block_txs)):
+                batch_put(HEADER_PREFIX + util.pack_be_uint64(height_start), header)
+                self.headers.append(header)
+                tx_count = self.tx_counts[height_start]
+                batch_put(BLOCK_HASH_PREFIX + util.pack_be_uint64(height_start), block_hash[::-1])
+                batch_put(TX_COUNT_PREFIX + util.pack_be_uint64(height_start), util.pack_be_uint64(tx_count))
+                height_start += 1
+                offset = 0
+                while offset < len(tx_hashes):
+                    batch_put(TX_HASH_PREFIX + util.pack_be_uint64(tx_num), tx_hashes[offset:offset + 32])
+                    batch_put(TX_NUM_PREFIX + tx_hashes[offset:offset + 32], util.pack_be_uint64(tx_num))
+                    batch_put(TX_PREFIX + tx_hashes[offset:offset + 32], txs[offset // 32])
+
+                    tx_num += 1
+                    offset += 32
+            flush_data.headers.clear()
+            flush_data.block_txs.clear()
+            flush_data.block_hashes.clear()
+            # flush_data.claim_txo_cache.clear()
+            # flush_data.support_txo_cache.clear()
+
+            self.fs_height = flush_data.height
+            self.fs_tx_count = flush_data.tx_count
+
+
+            # Then history
+            self.hist_flush_count += 1
+            flush_id = pack_be_uint16(self.hist_flush_count)
+            unflushed = self.hist_unflushed
+
+            for hashX in sorted(unflushed):
+                key = hashX + flush_id
+                batch_put(HASHX_HISTORY_PREFIX + key, unflushed[hashX].tobytes())
+            self.write_history_state(batch)
+
+            unflushed.clear()
+            self.hist_unflushed_count = 0
+
+
+            #########################
+
+            # Flush state last as it reads the wall time.
+            self.flush_utxo_db(batch, flush_data)
+
+            # self.flush_state(batch)
+            #
             now = time.time()
             self.wall_time += now - self.last_flush
             self.last_flush = now
             self.last_flush_tx_count = self.fs_tx_count
             self.write_utxo_state(batch)
 
+        # # Update and put the wall time again - otherwise we drop the
+        # # time it took to commit the batch
+        # # self.flush_state(self.db)
+        # now = time.time()
+        # self.wall_time += now - self.last_flush
+        # self.last_flush = now
+        # self.last_flush_tx_count = self.fs_tx_count
+        # self.write_utxo_state(batch)
+
+        elapsed = self.last_flush - start_time
+        self.logger.info(f'flush #{self.hist_flush_count:,d} took '
+                         f'{elapsed:.1f}s.  Height {flush_data.height:,d} '
+                         f'txs: {flush_data.tx_count:,d} ({tx_delta:+,d})')
+
+        # Catch-up stats
+        if self.db.for_sync:
+            flush_interval = self.last_flush - prior_flush
+            tx_per_sec_gen = int(flush_data.tx_count / self.wall_time)
+            tx_per_sec_last = 1 + int(tx_delta / flush_interval)
+            eta = estimate_txs_remaining() / tx_per_sec_last
+            self.logger.info(f'tx/sec since genesis: {tx_per_sec_gen:,d}, '
+                             f'since last flush: {tx_per_sec_last:,d}')
+            self.logger.info(f'sync time: {formatted_time(self.wall_time)}  '
+                             f'ETA: {formatted_time(eta)}')
+
+    # def flush_state(self, batch):
+    #     """Flush chain state to the batch."""
+    #     now = time.time()
+    #     self.wall_time += now - self.last_flush
+    #     self.last_flush = now
+    #     self.last_flush_tx_count = self.fs_tx_count
+    #     self.write_utxo_state(batch)
+
     def flush_backup(self, flush_data, touched):
         """Like flush_dbs() but when backing up.  All UTXOs are flushed."""
         assert not flush_data.headers
         assert not flush_data.block_txs
         assert flush_data.height < self.db_height
-        self.history.assert_flushed()
+        assert not self.hist_unflushed
 
         start_time = time.time()
         tx_delta = flush_data.tx_count - self.last_flush_tx_count
-
-        self.backup_fs(flush_data.height, flush_data.tx_count)
-        self.history.backup(touched, flush_data.tx_count)
-        with self.utxo_db.write_batch() as batch:
-            self.flush_utxo_db(batch, flush_data)
-            # Flush state last as it reads the wall time.
-            self.flush_state(batch)
-
-        elapsed = self.last_flush - start_time
-        self.logger.info(f'backup flush #{self.history.flush_count:,d} took '
-                         f'{elapsed:.1f}s.  Height {flush_data.height:,d} '
-                         f'txs: {flush_data.tx_count:,d} ({tx_delta:+,d})')
-
-    def backup_fs(self, height, tx_count):
-        """Back up during a reorg.  This just updates our pointers."""
-        while self.fs_height > height:
+        ###
+        while self.fs_height > flush_data.height:
             self.fs_height -= 1
             self.headers.pop()
-        self.fs_tx_count = tx_count
+        self.fs_tx_count = flush_data.tx_count
         # Truncate header_mc: header count is 1 more than the height.
-        self.header_mc.truncate(height + 1)
+        self.header_mc.truncate(flush_data.height + 1)
+
+        ###
+        # Not certain this is needed, but it doesn't hurt
+        self.hist_flush_count += 1
+        nremoves = 0
+
+        with self.db.write_batch() as batch:
+            tx_count = flush_data.tx_count
+            for hashX in sorted(touched):
+                deletes = []
+                puts = {}
+                for key, hist in self.db.iterator(prefix=HASHX_HISTORY_PREFIX + hashX, reverse=True):
+                    k = key[1:]
+                    a = array.array('I')
+                    a.frombytes(hist)
+                    # Remove all history entries >= tx_count
+                    idx = bisect_left(a, tx_count)
+                    nremoves += len(a) - idx
+                    if idx > 0:
+                        puts[k] = a[:idx].tobytes()
+                        break
+                    deletes.append(k)
+
+                for key in deletes:
+                    batch.delete(key)
+                for key, value in puts.items():
+                    batch.put(key, value)
+            self.write_history_state(batch)
+
+            self.flush_utxo_db(batch, flush_data)
+            # Flush state last as it reads the wall time.
+            now = time.time()
+            self.wall_time += now - self.last_flush
+            self.last_flush = now
+            self.last_flush_tx_count = self.fs_tx_count
+            self.write_utxo_state(batch)
+        self.logger.info(f'backing up removed {nremoves:,d} history entries')
+        elapsed = self.last_flush - start_time
+        self.logger.info(f'backup flush #{self.hist_flush_count:,d} took {elapsed:.1f}s. '
+                         f'Height {flush_data.height:,d} txs: {flush_data.tx_count:,d} ({tx_delta:+,d})')
 
     def raw_header(self, height):
         """Return the binary header at the given height."""
@@ -471,9 +603,8 @@ class LevelDB:
     def _fs_transactions(self, txids: Iterable[str]):
         unpack_be_uint64 = util.unpack_be_uint64
         tx_counts = self.tx_counts
-        tx_db_get = self.tx_db.get
+        tx_db_get = self.db.get
         tx_cache = self._tx_and_merkle_cache
-
         tx_infos = {}
 
         for tx_hash in txids:
@@ -531,11 +662,13 @@ class LevelDB:
         def read_history():
             db_height = self.db_height
             tx_counts = self.tx_counts
+            tx_db_get = self.db.get
+            pack_be_uint64 = util.pack_be_uint64
 
             cnt = 0
             txs = []
 
-            for hist in self.history.db.iterator(prefix=hashX, include_key=False):
+            for hist in self.db.iterator(prefix=HASHX_HISTORY_PREFIX + hashX, include_key=False):
                 a = array.array('I')
                 a.frombytes(hist)
                 for tx_num in a:
@@ -566,16 +699,11 @@ class LevelDB:
 
     def undo_key(self, height):
         """DB key for undo information at the given height."""
-        return b'U' + pack('>I', height)
+        return UNDO_PREFIX + pack('>I', height)
 
     def read_undo_info(self, height):
         """Read undo information from a file for the current height."""
-        return self.utxo_db.get(self.undo_key(height))
-
-    def flush_undo_infos(self, batch_put, undo_infos):
-        """undo_infos is a list of (undo_info, height) pairs."""
-        for undo_info, height in undo_infos:
-            batch_put(self.undo_key(height), b''.join(undo_info))
+        return self.db.get(self.undo_key(height))
 
     def raw_block_prefix(self):
         return 'block'
@@ -606,17 +734,16 @@ class LevelDB:
 
     def clear_excess_undo_info(self):
         """Clear excess undo info.  Only most recent N are kept."""
-        prefix = b'U'
         min_height = self.min_undo_height(self.db_height)
         keys = []
-        for key, hist in self.utxo_db.iterator(prefix=prefix):
+        for key, hist in self.db.iterator(prefix=UNDO_PREFIX):
             height, = unpack('>I', key[-4:])
             if height >= min_height:
                 break
             keys.append(key)
 
         if keys:
-            with self.utxo_db.write_batch() as batch:
+            with self.db.write_batch() as batch:
                 for key in keys:
                     batch.delete(key)
             self.logger.info(f'deleted {len(keys):,d} stale undo entries')
@@ -637,7 +764,7 @@ class LevelDB:
     # -- UTXO database
 
     def read_utxo_state(self):
-        state = self.utxo_db.get(b'state')
+        state = self.db.get(UTXO_STATE)
         if not state:
             self.db_height = -1
             self.db_tx_count = 0
@@ -680,7 +807,7 @@ class LevelDB:
         self.logger.info(f'height: {self.db_height:,d}')
         self.logger.info(f'tip: {hash_to_hex_str(self.db_tip)}')
         self.logger.info(f'tx count: {self.db_tx_count:,d}')
-        if self.utxo_db.for_sync:
+        if self.db.for_sync:
             self.logger.info(f'flushing DB cache at {self.env.cache_MB:,d} MB')
         if self.first_sync:
             self.logger.info(f'sync time so far: {util.formatted_time(self.wall_time)}')
@@ -697,11 +824,11 @@ class LevelDB:
             'first_sync': self.first_sync,
             'db_version': self.db_version,
         }
-        batch.put(b'state', repr(state).encode())
+        batch.put(UTXO_STATE, repr(state).encode())
 
     def set_flush_count(self, count):
         self.utxo_flush_count = count
-        with self.utxo_db.write_batch() as batch:
+        with self.db.write_batch() as batch:
             self.write_utxo_state(batch)
 
     async def all_utxos(self, hashX):
@@ -713,8 +840,8 @@ class LevelDB:
             fs_tx_hash = self.fs_tx_hash
             # Key: b'u' + address_hashX + tx_idx + tx_num
             # Value: the UTXO value as a 64-bit unsigned integer
-            prefix = b'u' + hashX
-            for db_key, db_value in self.utxo_db.iterator(prefix=prefix):
+            prefix = UTXO_PREFIX + hashX
+            for db_key, db_value in self.db.iterator(prefix=prefix):
                 tx_pos, tx_num = s_unpack('<HI', db_key[-6:])
                 value, = unpack('<Q', db_value)
                 tx_hash, height = fs_tx_hash(tx_num)
@@ -744,10 +871,10 @@ class LevelDB:
 
                 # Key: b'h' + compressed_tx_hash + tx_idx + tx_num
                 # Value: hashX
-                prefix = b'h' + tx_hash[:4] + idx_packed
+                prefix = HASHX_UTXO_PREFIX + tx_hash[:4] + idx_packed
 
                 # Find which entry, if any, the TX_HASH matches.
-                for db_key, hashX in self.utxo_db.iterator(prefix=prefix):
+                for db_key, hashX in self.db.iterator(prefix=prefix):
                     tx_num_packed = db_key[-4:]
                     tx_num, = unpack('<I', tx_num_packed)
                     hash, height = self.fs_tx_hash(tx_num)
@@ -765,8 +892,8 @@ class LevelDB:
                     return None
                 # Key: b'u' + address_hashX + tx_idx + tx_num
                 # Value: the UTXO value as a 64-bit unsigned integer
-                key = b'u' + hashX + suffix
-                db_value = self.utxo_db.get(key)
+                key = UTXO_PREFIX + hashX + suffix
+                db_value = self.db.get(key)
                 if not db_value:
                     # This can happen if the DB was updated between
                     # getting the hashXs and getting the UTXOs

lbry/wallet/server/merkle.py

@@ -43,10 +43,12 @@ class Merkle:
     def __init__(self, hash_func=double_sha256):
         self.hash_func = hash_func
 
-    def tree_depth(self, hash_count):
-        return self.branch_length(hash_count) + 1
+    @staticmethod
+    def tree_depth(hash_count):
+        return Merkle.branch_length(hash_count) + 1
 
-    def branch_length(self, hash_count):
+    @staticmethod
+    def branch_length(hash_count):
         """Return the length of a merkle branch given the number of hashes."""
         if not isinstance(hash_count, int):
             raise TypeError('hash_count must be an integer')
@@ -54,7 +56,8 @@ class Merkle:
             raise ValueError('hash_count must be at least 1')
         return ceil(log(hash_count, 2))
 
-    def branch_and_root(self, hashes, index, length=None):
+    @staticmethod
+    def branch_and_root(hashes, index, length=None, hash_func=double_sha256):
         """Return a (merkle branch, merkle_root) pair given hashes, and the
         index of one of those hashes.
         """
@@ -64,7 +67,7 @@ class Merkle:
         # This also asserts hashes is not empty
         if not 0 <= index < len(hashes):
             raise ValueError(f"index '{index}/{len(hashes)}' out of range")
-        natural_length = self.branch_length(len(hashes))
+        natural_length = Merkle.branch_length(len(hashes))
         if length is None:
             length = natural_length
         else:
@@ -73,7 +76,6 @@ class Merkle:
             if length < natural_length:
                 raise ValueError('length out of range')
 
-        hash_func = self.hash_func
         branch = []
         for _ in range(length):
             if len(hashes) & 1:
@@ -85,44 +87,47 @@ class Merkle:
 
         return branch, hashes[0]
 
-    def root(self, hashes, length=None):
+    @staticmethod
+    def root(hashes, length=None):
         """Return the merkle root of a non-empty iterable of binary hashes."""
-        branch, root = self.branch_and_root(hashes, 0, length)
+        branch, root = Merkle.branch_and_root(hashes, 0, length)
         return root
 
-    def root_from_proof(self, hash, branch, index):
-        """Return the merkle root given a hash, a merkle branch to it, and
-        its index in the hashes array.
+    # @staticmethod
+    # def root_from_proof(hash, branch, index, hash_func=double_sha256):
+    #     """Return the merkle root given a hash, a merkle branch to it, and
+    #     its index in the hashes array.
+    #
+    #     branch is an iterable sorted deepest to shallowest.  If the
+    #     returned root is the expected value then the merkle proof is
+    #     verified.
+    #
+    #     The caller should have confirmed the length of the branch with
+    #     branch_length().  Unfortunately this is not easily done for
+    #     bitcoin transactions as the number of transactions in a block
+    #     is unknown to an SPV client.
+    #     """
+    #     for elt in branch:
+    #         if index & 1:
+    #             hash = hash_func(elt + hash)
+    #         else:
+    #             hash = hash_func(hash + elt)
+    #         index >>= 1
+    #     if index:
+    #         raise ValueError('index out of range for branch')
+    #     return hash
 
-        branch is an iterable sorted deepest to shallowest.  If the
-        returned root is the expected value then the merkle proof is
-        verified.
-
-        The caller should have confirmed the length of the branch with
-        branch_length().  Unfortunately this is not easily done for
-        bitcoin transactions as the number of transactions in a block
-        is unknown to an SPV client.
-        """
-        hash_func = self.hash_func
-        for elt in branch:
-            if index & 1:
-                hash = hash_func(elt + hash)
-            else:
-                hash = hash_func(hash + elt)
-            index >>= 1
-        if index:
-            raise ValueError('index out of range for branch')
-        return hash
-
-    def level(self, hashes, depth_higher):
+    @staticmethod
+    def level(hashes, depth_higher):
         """Return a level of the merkle tree of hashes the given depth
         higher than the bottom row of the original tree."""
         size = 1 << depth_higher
-        root = self.root
+        root = Merkle.root
         return [root(hashes[n: n + size], depth_higher)
                 for n in range(0, len(hashes), size)]
 
-    def branch_and_root_from_level(self, level, leaf_hashes, index,
+    @staticmethod
+    def branch_and_root_from_level(level, leaf_hashes, index,
                                    depth_higher):
         """Return a (merkle branch, merkle_root) pair when a merkle-tree has a
         level cached.
@@ -146,10 +151,10 @@ class Merkle:
         if not isinstance(leaf_hashes, list):
             raise TypeError("leaf_hashes must be a list")
         leaf_index = (index >> depth_higher) << depth_higher
-        leaf_branch, leaf_root = self.branch_and_root(
+        leaf_branch, leaf_root = Merkle.branch_and_root(
             leaf_hashes, index - leaf_index, depth_higher)
         index >>= depth_higher
-        level_branch, root = self.branch_and_root(level, index)
+        level_branch, root = Merkle.branch_and_root(level, index)
         # Check last so that we know index is in-range
         if leaf_root != level[index]:
             raise ValueError('leaf hashes inconsistent with level')