diff --git a/lib/coins.py b/lib/coins.py
index 9a1d10c..81ba382 100644
--- a/lib/coins.py
+++ b/lib/coins.py
@@ -1,4 +1,4 @@
-# Copyright (c) 2016, Neil Booth
+# Copyright (c) 2016-2017, Neil Booth
 #
 # All rights reserved.
 #
@@ -13,13 +13,14 @@ necessary for appropriate handling.
 
 from decimal import Decimal
 from functools import partial
+from hashlib import sha256
 import inspect
 import re
 import struct
 import sys
 
-from lib.hash import Base58, hash160, double_sha256, hash_to_str
-from lib.script import ScriptPubKey, Script
+from lib.hash import Base58, hash160, ripemd160, double_sha256, hash_to_str
+from lib.script import ScriptPubKey
 from lib.tx import Deserializer
 from lib.util import cachedproperty, subclasses
 
@@ -37,9 +38,9 @@ class Coin(object):
     RPC_URL_REGEX = re.compile('.+@[^:]+(:[0-9]+)?')
     VALUE_PER_COIN = 100000000
     CHUNK_SIZE=2016
-    STRANGE_VERBYTE = 0xff
     IRC_SERVER = "irc.freenode.net"
     IRC_PORT = 6667
+    HASHX_LEN = 11
 
     @classmethod
     def lookup_coin_class(cls, name, net):
@@ -70,20 +71,28 @@ class Coin(object):
     def daemon_urls(cls, urls):
         return [cls.sanitize_url(url) for url in urls.split(',')]
 
+    @classmethod
+    def hashX_from_script(cls, script):
+        '''Returns a hashX from a script.'''
+        script = ScriptPubKey.hashX_script(script)
+        if script is None:
+            return None
+        return sha256(script).digest()[:cls.HASHX_LEN]
+
     @cachedproperty
-    def hash168_handlers(cls):
+    def address_handlers(cls):
         return ScriptPubKey.PayToHandlers(
-            address = cls.P2PKH_hash168_from_hash160,
-            script_hash = cls.P2SH_hash168_from_hash160,
-            pubkey = cls.P2PKH_hash168_from_pubkey,
-            unspendable = cls.hash168_from_unspendable,
-            strange = cls.hash168_from_strange,
+            address = cls.P2PKH_address_from_hash160,
+            script_hash = cls.P2SH_address_from_hash160,
+            pubkey = cls.P2PKH_address_from_pubkey,
+            unspendable = lambda : None,
+            strange = lambda script: None,
         )
 
     @classmethod
-    def hash168_from_script(cls):
-        '''Returns a function that is passed a script to return a hash168.'''
-        return partial(ScriptPubKey.pay_to, cls.hash168_handlers)
+    def address_from_script(cls, script):
+        '''Given a pk_script, return the adddress it pays to, or None.'''
+        return ScriptPubKey.pay_to(cls.address_handlers, script)
 
     @staticmethod
     def lookup_xverbytes(verbytes):
@@ -97,65 +106,26 @@ class Coin(object):
         raise CoinError('version bytes unrecognised')
 
     @classmethod
-    def address_to_hash168(cls, addr):
-        '''Return a 21-byte hash given an address.
-
-        This is the hash160 prefixed by the address version byte.
-        '''
-        result = Base58.decode_check(addr)
-        if len(result) != 21:
-            raise CoinError('invalid address: {}'.format(addr))
-        return result
-
-    @classmethod
-    def hash168_to_address(cls, hash168):
-        '''Return an address given a 21-byte hash.'''
-        return Base58.encode_check(hash168)
-
-    @classmethod
-    def hash168_from_unspendable(cls):
-        '''Return a hash168 for an unspendable script.'''
-        return None
-
-    @classmethod
-    def hash168_from_strange(cls, script):
-        '''Return a hash168 for a strange script.'''
-        return bytes([cls.STRANGE_VERBYTE]) + hash160(script)
-
-    @classmethod
-    def P2PKH_hash168_from_hash160(cls, hash160):
-        '''Return a hash168 if hash160 is 160 bits otherwise None.'''
-        if len(hash160) == 20:
-            return bytes([cls.P2PKH_VERBYTE]) + hash160
-        return None
-
-    @classmethod
-    def P2PKH_hash168_from_pubkey(cls, pubkey):
-        return cls.P2PKH_hash168_from_hash160(hash160(pubkey))
+    def address_to_hashX(cls, address):
+        '''Return a hashX given a coin address.'''
+        return cls.hashX_from_script(cls.pay_to_address_script(address))
 
     @classmethod
     def P2PKH_address_from_hash160(cls, hash160):
         '''Return a P2PKH address given a public key.'''
         assert len(hash160) == 20
-        return Base58.encode_check(cls.P2PKH_hash168_from_hash160(hash160))
+        return Base58.encode_check(bytes([cls.P2PKH_VERBYTE]) + hash160)
 
     @classmethod
     def P2PKH_address_from_pubkey(cls, pubkey):
         '''Return a coin address given a public key.'''
         return cls.P2PKH_address_from_hash160(hash160(pubkey))
 
-    @classmethod
-    def P2SH_hash168_from_hash160(cls, hash160):
-        '''Return a hash168 if hash160 is 160 bits otherwise None.'''
-        if len(hash160) == 20:
-            return bytes([cls.P2SH_VERBYTE]) + hash160
-        return None
-
     @classmethod
     def P2SH_address_from_hash160(cls, hash160):
         '''Return a coin address given a hash160.'''
         assert len(hash160) == 20
-        return Base58.encode_check(cls.P2SH_hash168_from_hash160(hash160))
+        return Base58.encode_check(bytes([cls.P2SH_VERBYTE]) + hash160)
 
     @classmethod
     def multisig_address(cls, m, pubkeys):
@@ -195,7 +165,7 @@ class Coin(object):
         if len(raw) == 21:
             verbyte, hash_bytes = raw[0], raw[1:]
 
-        if verbyte == cls.P2PKH_VERYBYTE:
+        if verbyte == cls.P2PKH_VERBYTE:
             return ScriptPubKey.P2PKH_script(hash_bytes)
         if verbyte == cls.P2SH_VERBYTE:
             return ScriptPubKey.P2SH_script(hash_bytes)
@@ -262,9 +232,9 @@ class Bitcoin(Coin):
     WIF_BYTE = 0x80
     GENESIS_HASH=(b'000000000019d6689c085ae165831e93'
                   b'4ff763ae46a2a6c172b3f1b60a8ce26f')
-    TX_COUNT = 142791895
-    TX_COUNT_HEIGHT = 420976
-    TX_PER_BLOCK = 1600
+    TX_COUNT = 156335304
+    TX_COUNT_HEIGHT = 429972
+    TX_PER_BLOCK = 1800
     IRC_PREFIX = "E_"
     IRC_CHANNEL = "#electrum"
     RPC_PORT = 8332
diff --git a/lib/jsonrpc.py b/lib/jsonrpc.py
index 7301076..ccf46e1 100644
--- a/lib/jsonrpc.py
+++ b/lib/jsonrpc.py
@@ -290,8 +290,8 @@ class JSONRPC(asyncio.Protocol, LoggedClass):
         except TypeError:
             msg = 'JSON encoding failure: {}'.format(payload)
             self.log_error(msg)
-            return self.json_error(msg, self.INTERNAL_ERROR,
-                                   self.payload_id(payload))
+            return self.send_json_error(msg, self.INTERNAL_ERROR,
+                                        self.payload_id(payload))
 
         self.check_oversized_request(len(binary))
         self.send_count += 1
diff --git a/lib/script.py b/lib/script.py
index 6391c81..4c2b65a 100644
--- a/lib/script.py
+++ b/lib/script.py
@@ -12,6 +12,7 @@ import struct
 from collections import namedtuple
 
 from lib.enum import Enumeration
+from lib.hash import hash160
 
 
 class ScriptError(Exception):
@@ -82,6 +83,27 @@ class ScriptPubKey(object):
     PayToHandlers = namedtuple('PayToHandlers', 'address script_hash pubkey '
                                'unspendable strange')
 
+    @classmethod
+    def hashX_script(cls, script):
+        '''Return None if the script is provably unspendable.  Return a
+        pay-to-pubkey-hash script if it is pay-to-pubkey, otherwise
+        return script.
+        '''
+        if script:
+            op = script[0]
+            if op == OpCodes.OP_RETURN:
+                return None
+            if op <= OpCodes.OP_PUSHDATA4:
+                try:
+                    ops = Script.get_ops(script)
+                except ScriptError:
+                    pass
+                else:
+                    if _match_ops(ops, cls.TO_PUBKEY_OPS):
+                        pubkey = ops[0][1]
+                        script = ScriptPubKey.P2PKH_script(hash160(pubkey))
+        return script
+
     @classmethod
     def pay_to(cls, handlers, script):
         '''Parse a script, invoke the appropriate handler and
diff --git a/query.py b/query.py
index 671b91d..05ae277 100755
--- a/query.py
+++ b/query.py
@@ -26,15 +26,17 @@ def count_entries(db):
         utxos += 1
     print("UTXO count:", utxos)
 
-    hash168 = 0
+    hashX = 0
     for key in db.iterator(prefix=b'h', include_value=False):
-        hash168 += 1
-    print("Hash168 count:", hash168)
+        hashX += 1
+    print("HashX count:", hashX)
 
     hist = 0
-    for key in db.iterator(prefix=b'H', include_value=False):
+    hist_len = 0
+    for key, value in db.iterator(prefix=b'H'):
         hist += 1
-    print("History rows:", hist)
+        hist_len += len(value) // 4
+    print("History rows {:,d} entries {:,d}", hist, hist_len)
 
 
 def main():
@@ -52,27 +54,20 @@ def main():
         limit = 10
     for addr in sys.argv[argc:]:
         print('Address: ', addr)
-        hash168 = coin.address_to_hash168(addr)
-
-        hist = 0
-        hist_len = 0
-        for key, value in bp.db.iterator(prefix=b'H'+hash168):
-            hist += 1
-            hist_len += len(value) // 4
-        print("History: {:,d} rows with {:,d} entries".format(hist, hist_len))
+        hashX = coin.address_to_hashX(addr)
 
         n = None
-        for n, (tx_hash, height) in enumerate(bp.get_history(hash168, limit)):
+        for n, (tx_hash, height) in enumerate(bp.get_history(hashX, limit)):
             print('History #{:d}: hash: {} height: {:d}'
                   .format(n + 1, hash_to_str(tx_hash), height))
         n = None
-        for n, utxo in enumerate(bp.get_utxos(hash168, limit)):
+        for n, utxo in enumerate(bp.get_utxos(hashX, limit)):
             print('UTXOs #{:d}: hash: {} pos: {:d} height: {:d} value: {:d}'
                   .format(n + 1, hash_to_str(utxo.tx_hash),
                           utxo.tx_pos, utxo.height, utxo.value))
         if n is None:
             print('No UTXOs')
-        balance = bp.get_balance(hash168)
+        balance = bp.get_balance(hashX)
         print('Balance: {} {}'.format(coin.decimal_value(balance),
                                       coin.SHORTNAME))
 
diff --git a/server/block_processor.py b/server/block_processor.py
index 8faa7a8..40b2324 100644
--- a/server/block_processor.py
+++ b/server/block_processor.py
@@ -172,8 +172,7 @@ class BlockProcessor(server.db.DB):
         self.caught_up_event = asyncio.Event()
 
         # Meta
-        self.utxo_MB = env.utxo_MB
-        self.hist_MB = env.hist_MB
+        self.cache_MB = env.cache_MB
         self.next_cache_check = 0
 
         # Headers and tx_hashes have one entry per block
@@ -194,10 +193,8 @@ class BlockProcessor(server.db.DB):
 
         # Log state
         if self.first_sync:
-            self.logger.info('flushing UTXO cache at {:,d} MB'
-                             .format(self.utxo_MB))
-            self.logger.info('flushing history cache at {:,d} MB'
-                             .format(self.hist_MB))
+            self.logger.info('flushing DB cache at {:,d} MB'
+                             .format(self.cache_MB))
 
     async def main_loop(self, touched):
         '''Main loop for block processing.'''
@@ -242,7 +239,7 @@ class BlockProcessor(server.db.DB):
             touched.clear()
             if time.time() > self.next_cache_check:
                 self.check_cache_size()
-                self.next_cache_check = time.time() + 60
+                self.next_cache_check = time.time() + 30
 
         if not self.first_sync:
             s = '' if len(blocks) == 1 else 's'
@@ -391,8 +388,8 @@ class BlockProcessor(server.db.DB):
 
         flush_id = pack('>H', self.flush_count)
 
-        for hash168, hist in self.history.items():
-            key = b'H' + hash168 + flush_id
+        for hashX, hist in self.history.items():
+            key = b'H' + hashX + flush_id
             batch.put(key, hist.tobytes())
 
         if self.first_sync:
@@ -415,10 +412,10 @@ class BlockProcessor(server.db.DB):
         self.tx_hashes = []
         self.headers = []
 
-    def backup_flush(self, hash168s):
+    def backup_flush(self, hashXs):
         '''Like flush() but when backing up.  All UTXOs are flushed.
 
-        hash168s - sequence of hash168s which were touched by backing
+        hashXs - sequence of hashXs which were touched by backing
         up.  Searched for history entries to remove after the backup
         height.
         '''
@@ -430,7 +427,7 @@ class BlockProcessor(server.db.DB):
 
         with self.db.write_batch() as batch:
             # Flush state last as it reads the wall time.
-            self.backup_history(batch, hash168s)
+            self.backup_history(batch, hashXs)
             self.flush_utxos(batch)
             self.flush_state(batch)
 
@@ -444,10 +441,10 @@ class BlockProcessor(server.db.DB):
                                  self.last_flush - flush_start,
                                  self.height, self.tx_count))
 
-    def backup_history(self, batch, hash168s):
+    def backup_history(self, batch, hashXs):
         nremoves = 0
-        for hash168 in sorted(hash168s):
-            prefix = b'H' + hash168
+        for hashX in sorted(hashXs):
+            prefix = b'H' + hashX
             deletes = []
             puts = {}
             for key, hist in self.db.iterator(prefix=prefix, reverse=True):
@@ -472,17 +469,15 @@ class BlockProcessor(server.db.DB):
         assert not self.tx_hashes
 
         self.logger.info('backing up removed {:,d} history entries from '
-                         '{:,d} addresses'.format(nremoves, len(hash168s)))
+                         '{:,d} addresses'.format(nremoves, len(hashXs)))
 
     def check_cache_size(self):
         '''Flush a cache if it gets too big.'''
         # Good average estimates based on traversal of subobjects and
-        # requesting size from Python (see deep_getsizeof).  For
-        # whatever reason Python O/S mem usage is typically +30% or
-        # more, so we scale our already bloated object sizes.
-        one_MB = int(1048576 / 1.3)
-        utxo_cache_size = len(self.utxo_cache) * 187
-        db_deletes_size = len(self.db_deletes) * 61
+        # requesting size from Python (see deep_getsizeof).
+        one_MB = 1000*1000
+        utxo_cache_size = len(self.utxo_cache) * 205
+        db_deletes_size = len(self.db_deletes) * 57
         hist_cache_size = len(self.history) * 180 + self.history_size * 4
         tx_hash_size = (self.tx_count - self.fs_tx_count) * 74
         utxo_MB = (db_deletes_size + utxo_cache_size) // one_MB
@@ -493,9 +488,10 @@ class BlockProcessor(server.db.DB):
                          .format(self.height, self.daemon.cached_height(),
                                  utxo_MB, hist_MB))
 
-        # Flush if a cache is too big
-        if utxo_MB >= self.utxo_MB or hist_MB >= self.hist_MB:
-            self.flush(utxo_MB >= self.utxo_MB)
+        # Flush history if it takes up over 20% of cache memory.
+        # Flush UTXOs once they take up 80% of cache memory.
+        if utxo_MB + hist_MB >= self.cache_MB or hist_MB >= self.cache_MB // 5:
+            self.flush(utxo_MB >= self.cache_MB * 4 // 5)
 
     def fs_advance_block(self, header, tx_hashes, txs):
         '''Update unflushed FS state for a new block.'''
@@ -525,15 +521,15 @@ class BlockProcessor(server.db.DB):
         history = self.history
         history_size = self.history_size
         tx_num = self.tx_count
-        script_hash168 = self.coin.hash168_from_script()
+        script_hashX = self.coin.hashX_from_script
         s_pack = pack
         put_utxo = self.utxo_cache.__setitem__
         spend_utxo = self.spend_utxo
         undo_info_append = undo_info.append
 
         for tx, tx_hash in zip(txs, tx_hashes):
-            hash168s = set()
-            add_hash168 = hash168s.add
+            hashXs = set()
+            add_hashX = hashXs.add
             tx_numb = s_pack('<I', tx_num)
 
             # Spend the inputs
@@ -541,21 +537,21 @@ class BlockProcessor(server.db.DB):
                 for txin in tx.inputs:
                     cache_value = spend_utxo(txin.prev_hash, txin.prev_idx)
                     undo_info_append(cache_value)
-                    add_hash168(cache_value[:21])
+                    add_hashX(cache_value[:-12])
 
             # Add the new UTXOs
             for idx, txout in enumerate(tx.outputs):
-                # Get the hash168.  Ignore unspendable outputs
-                hash168 = script_hash168(txout.pk_script)
-                if hash168:
-                    add_hash168(hash168)
+                # Get the hashX.  Ignore unspendable outputs
+                hashX = script_hashX(txout.pk_script)
+                if hashX:
+                    add_hashX(hashX)
                     put_utxo(tx_hash + s_pack('<H', idx),
-                             hash168 + tx_numb + s_pack('<Q', txout.value))
+                             hashX + tx_numb + s_pack('<Q', txout.value))
 
-            for hash168 in hash168s:
-                history[hash168].append(tx_num)
-            history_size += len(hash168s)
-            touched.update(hash168s)
+            for hashX in hashXs:
+                history[hashX].append(tx_num)
+            history_size += len(hashXs)
+            touched.update(hashXs)
             tx_num += 1
 
         self.tx_count = tx_num
@@ -605,7 +601,8 @@ class BlockProcessor(server.db.DB):
         s_pack = pack
         put_utxo = self.utxo_cache.__setitem__
         spend_utxo = self.spend_utxo
-        script_hash168 = self.coin.hash168_from_script()
+        script_hashX = self.coin.hashX_from_script
+        undo_entry_len = 12 + self.coin.HASHX_LEN
 
         rtxs = reversed(txs)
         rtx_hashes = reversed(tx_hashes)
@@ -614,19 +611,19 @@ class BlockProcessor(server.db.DB):
             for idx, txout in enumerate(tx.outputs):
                 # Spend the TX outputs.  Be careful with unspendable
                 # outputs - we didn't save those in the first place.
-                hash168 = script_hash168(txout.pk_script)
-                if hash168:
+                hashX = script_hashX(txout.pk_script)
+                if hashX:
                     cache_value = spend_utxo(tx_hash, idx)
-                    touched.add(cache_value[:21])
+                    touched.add(cache_value[:-12])
 
             # Restore the inputs
             if not tx.is_coinbase:
                 for txin in reversed(tx.inputs):
-                    n -= 33
-                    undo_item = undo_info[n:n + 33]
+                    n -= undo_entry_len
+                    undo_item = undo_info[n:n + undo_entry_len]
                     put_utxo(txin.prev_hash + s_pack('<H', txin.prev_idx),
                              undo_item)
-                    touched.add(undo_item[:21])
+                    touched.add(undo_item[:-12])
 
         assert n == 0
         self.tx_count -= len(txs)
@@ -642,12 +639,13 @@ class BlockProcessor(server.db.DB):
     binary keys and values.
 
       Key:    TX_HASH + TX_IDX           (32 + 2 = 34 bytes)
-      Value:  HASH168 + TX_NUM + VALUE   (21 + 4 + 8 = 33 bytes)
+      Value:  HASHX + TX_NUM + VALUE     (11 + 4 + 8 = 23 bytes)
 
-    That's 67 bytes of raw data.  Python dictionary overhead means
-    each entry actually uses about 187 bytes of memory.  So over 5
-    million UTXOs can fit in 1GB of RAM.  There are approximately 42
-    million UTXOs on bitcoin mainnet at height 433,000.
+    That's 57 bytes of raw data in-memory.  Python dictionary overhead
+    means each entry actually uses about 205 bytes of memory.  So
+    almost 5 million UTXOs can fit in 1GB of RAM.  There are
+    approximately 42 million UTXOs on bitcoin mainnet at height
+    433,000.
 
     Semantics:
 
@@ -670,11 +668,11 @@ class BlockProcessor(server.db.DB):
 
     To this end we maintain two "tables", one for each point above:
 
-      1.  Key: b'u' + address_hash168 + tx_idx + tx_num
+      1.  Key: b'u' + address_hashX + tx_idx + tx_num
           Value: the UTXO value as a 64-bit unsigned integer
 
       2.  Key: b'h' + compressed_tx_hash + tx_idx + tx_num
-          Value: hash168
+          Value: hashX
 
     The compressed tx hash is just the first few bytes of the hash of
     the tx in which the UTXO was created.  As this is not unique there
@@ -700,12 +698,12 @@ class BlockProcessor(server.db.DB):
         # Spend it from the DB.
 
         # Key: b'h' + compressed_tx_hash + tx_idx + tx_num
-        # Value: hash168
+        # Value: hashX
         prefix = b'h' + tx_hash[:4] + idx_packed
-        candidates = {db_key: hash168 for db_key, hash168
+        candidates = {db_key: hashX for db_key, hashX
                       in self.db.iterator(prefix=prefix)}
 
-        for hdb_key, hash168 in candidates.items():
+        for hdb_key, hashX in candidates.items():
             tx_num_packed = hdb_key[-4:]
 
             if len(candidates) > 1:
@@ -715,15 +713,15 @@ class BlockProcessor(server.db.DB):
                     assert hash is not None  # Should always be found
                     continue
 
-            # Key: b'u' + address_hash168 + tx_idx + tx_num
+            # Key: b'u' + address_hashX + tx_idx + tx_num
             # Value: the UTXO value as a 64-bit unsigned integer
-            udb_key = b'u' + hash168 + hdb_key[-6:]
+            udb_key = b'u' + hashX + hdb_key[-6:]
             utxo_value_packed = self.db.get(udb_key)
             if utxo_value_packed:
                 # Remove both entries for this UTXO
                 self.db_deletes.append(hdb_key)
                 self.db_deletes.append(udb_key)
-                return hash168 + tx_num_packed + utxo_value_packed
+                return hashX + tx_num_packed + utxo_value_packed
 
         raise ChainError('UTXO {} / {:,d} not found in "h" table'
                          .format(hash_to_str(tx_hash), tx_idx))
@@ -743,11 +741,11 @@ class BlockProcessor(server.db.DB):
 
         batch_put = batch.put
         for cache_key, cache_value in self.utxo_cache.items():
-            # suffix = tx_num + tx_idx
-            hash168 = cache_value[:21]
-            suffix =  cache_key[-2:] + cache_value[21:25]
-            batch_put(b'h' + cache_key[:4] + suffix, hash168)
-            batch_put(b'u' + hash168 + suffix, cache_value[25:])
+            # suffix = tx_idx + tx_num
+            hashX = cache_value[:-12]
+            suffix =  cache_key[-2:] + cache_value[-12:-8]
+            batch_put(b'h' + cache_key[:4] + suffix, hashX)
+            batch_put(b'u' + hashX + suffix, cache_value[-8:])
 
         if self.first_sync:
             self.logger.info('flushed {:,d} blocks with {:,d} txs, {:,d} UTXO '
diff --git a/server/controller.py b/server/controller.py
index 1a4b06a..3febb59 100644
--- a/server/controller.py
+++ b/server/controller.py
@@ -73,20 +73,20 @@ class Controller(util.LoggedClass):
         env.max_send = max(350000, env.max_send)
         self.setup_bands()
 
-    async def mempool_transactions(self, hash168):
+    async def mempool_transactions(self, hashX):
         '''Generate (hex_hash, tx_fee, unconfirmed) tuples for mempool
-        entries for the hash168.
+        entries for the hashX.
 
         unconfirmed is True if any txin is unconfirmed.
         '''
-        return await self.mempool.transactions(hash168)
+        return await self.mempool.transactions(hashX)
 
-    def mempool_value(self, hash168):
-        '''Return the unconfirmed amount in the mempool for hash168.
+    def mempool_value(self, hashX):
+        '''Return the unconfirmed amount in the mempool for hashX.
 
         Can be positive or negative.
         '''
-        return self.mempool.value(hash168)
+        return self.mempool.value(hashX)
 
     def sent_tx(self, tx_hash):
         '''Call when a TX is sent.  Tells mempool to prioritize it.'''
@@ -255,8 +255,8 @@ class Controller(util.LoggedClass):
 
             # Invalidate caches
             hc = self.history_cache
-            for hash168 in set(hc).intersection(touched):
-                del hc[hash168]
+            for hashX in set(hc).intersection(touched):
+                del hc[hashX]
             if self.bp.db_height != self.height:
                 self.height = self.bp.db_height
                 self.header_cache.clear()
@@ -286,10 +286,10 @@ class Controller(util.LoggedClass):
         self.header_cache[height] = header
         return header
 
-    async def async_get_history(self, hash168):
+    async def async_get_history(self, hashX):
         '''Get history asynchronously to reduce latency.'''
-        if hash168 in self.history_cache:
-            return self.history_cache[hash168]
+        if hashX in self.history_cache:
+            return self.history_cache[hashX]
 
         def job():
             # History DoS limit.  Each element of history is about 99
@@ -297,11 +297,11 @@ class Controller(util.LoggedClass):
             # on bloated history requests, and uses a smaller divisor
             # so large requests are logged before refusing them.
             limit = self.env.max_send // 97
-            return list(self.bp.get_history(hash168, limit=limit))
+            return list(self.bp.get_history(hashX, limit=limit))
 
         loop = asyncio.get_event_loop()
         history = await loop.run_in_executor(None, job)
-        self.history_cache[hash168] = history
+        self.history_cache[hashX] = history
         return history
 
     async def shutdown(self):
diff --git a/server/db.py b/server/db.py
index b5ec12d..143d4e9 100644
--- a/server/db.py
+++ b/server/db.py
@@ -31,7 +31,7 @@ class DB(LoggedClass):
     it was shutdown uncleanly.
     '''
 
-    DB_VERSIONS = [3]
+    DB_VERSIONS = [4]
 
     class MissingUTXOError(Exception):
         '''Raised if a mempool tx input UTXO couldn't be found.'''
@@ -319,7 +319,7 @@ class DB(LoggedClass):
         assert isinstance(limit, int) and limit >= 0
         return limit
 
-    def get_history(self, hash168, limit=1000):
+    def get_history(self, hashX, limit=1000):
         '''Generator that returns an unpruned, sorted list of (tx_hash,
         height) tuples of confirmed transactions that touched the address,
         earliest in the blockchain first.  Includes both spending and
@@ -327,7 +327,7 @@ class DB(LoggedClass):
         Set limit to None to get them all.
         '''
         limit = self._resolve_limit(limit)
-        prefix = b'H' + hash168
+        prefix = b'H' + hashX
         for key, hist in self.db.iterator(prefix=prefix):
             a = array.array('I')
             a.frombytes(hist)
@@ -337,20 +337,20 @@ class DB(LoggedClass):
                 yield self.fs_tx_hash(tx_num)
                 limit -= 1
 
-    def get_balance(self, hash168):
+    def get_balance(self, hashX):
         '''Returns the confirmed balance of an address.'''
-        return sum(utxo.value for utxo in self.get_utxos(hash168, limit=None))
+        return sum(utxo.value for utxo in self.get_utxos(hashX, limit=None))
 
-    def get_utxos(self, hash168, limit=1000):
+    def get_utxos(self, hashX, limit=1000):
         '''Generator that yields all UTXOs for an address sorted in no
         particular order.  By default yields at most 1000 entries.
         Set limit to None to get them all.
         '''
         limit = self._resolve_limit(limit)
         s_unpack = unpack
-        # Key: b'u' + address_hash168 + tx_idx + tx_num
+        # Key: b'u' + address_hashX + tx_idx + tx_num
         # Value: the UTXO value as a 64-bit unsigned integer
-        prefix = b'u' + hash168
+        prefix = b'u' + hashX
         for db_key, db_value in self.db.iterator(prefix=prefix):
             if limit == 0:
                 return
@@ -360,56 +360,43 @@ class DB(LoggedClass):
             tx_hash, height = self.fs_tx_hash(tx_num)
             yield UTXO(tx_num, tx_pos, tx_hash, height, value)
 
-    def get_utxo_hash168(self, tx_hash, index):
-        '''Returns the hash168 for a UTXO.
-
-        Used only for electrum client command-line requests.
-        '''
-        hash168 = None
-        if 0 <= index <= 65535:
-            idx_packed = pack('<H', index)
-            hash168, tx_num_packed = self.db_hash168(tx_hash, idx_packed)
-        return hash168
-
-    def db_hash168(self, tx_hash, idx_packed):
-        '''Return (hash168, tx_num_packed) for the given TXO.
+    def db_hashX(self, tx_hash, idx_packed):
+        '''Return (hashX, tx_num_packed) for the given TXO.
 
         Both are None if not found.'''
         # Key: b'h' + compressed_tx_hash + tx_idx + tx_num
-        # Value: hash168
+        # Value: hashX
         prefix = b'h' + tx_hash[:4] + idx_packed
 
         # Find which entry, if any, the TX_HASH matches.
-        for db_key, hash168 in self.db.iterator(prefix=prefix):
-            assert len(hash168) == 21
-
+        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)
             if hash == tx_hash:
-                return hash168, tx_num_packed
+                return hashX, tx_num_packed
 
         return None, None
 
     def db_utxo_lookup(self, tx_hash, tx_idx):
-        '''Given a prevout return a (hash168, value) pair.
+        '''Given a prevout return a (hashX, value) pair.
 
         Raises MissingUTXOError if the UTXO is not found.  Used by the
         mempool code.
         '''
         idx_packed = pack('<H', tx_idx)
-        hash168, tx_num_packed = self.db_hash168(tx_hash, idx_packed)
-        if not hash168:
+        hashX, tx_num_packed = self.db_hashX(tx_hash, idx_packed)
+        if not hashX:
             # This can happen when the daemon is a block ahead of us
             # and has mempool txs spending outputs from that new block
             raise self.MissingUTXOError
 
-        # Key: b'u' + address_hash168 + tx_idx + tx_num
+        # Key: b'u' + address_hashX + tx_idx + tx_num
         # Value: the UTXO value as a 64-bit unsigned integer
-        key = b'u' + hash168 + idx_packed + tx_num_packed
+        key = b'u' + hashX + idx_packed + tx_num_packed
         db_value = self.db.get(key)
         if not db_value:
             raise self.DBError('UTXO {} / {:,d} in one table only'
                                .format(hash_to_str(tx_hash), tx_idx))
         value, = unpack('<Q', db_value)
-        return hash168, value
+        return hashX, value
diff --git a/server/env.py b/server/env.py
index b7e5140..15d8137 100644
--- a/server/env.py
+++ b/server/env.py
@@ -22,12 +22,12 @@ class Env(LoggedClass):
 
     def __init__(self):
         super().__init__()
+        self.obsolete(['UTXO_MB', 'HIST_MB'])
         coin_name = self.default('COIN', 'Bitcoin')
         network = self.default('NETWORK', 'mainnet')
         self.coin = Coin.lookup_coin_class(coin_name, network)
         self.db_dir = self.required('DB_DIRECTORY')
-        self.utxo_MB = self.integer('UTXO_MB', 1000)
-        self.hist_MB = self.integer('HIST_MB', 300)
+        self.cache_MB = self.integer('CACHE_MB', 1250)
         self.host = self.default('HOST', 'localhost')
         self.reorg_limit = self.integer('REORG_LIMIT', self.coin.REORG_LIMIT)
         self.daemon_url = self.required('DAEMON_URL')
@@ -88,3 +88,9 @@ class Env(LoggedClass):
         except:
             raise self.Error('cannot convert envvar {} value {} to an integer'
                              .format(envvar, value))
+
+    def obsolete(self, envvars):
+        bad = [envvar for envvar in envvars if environ.get(envvar)]
+        if bad:
+            raise self.Error('remove obsolete environment variables {}'
+                             .format(bad))
diff --git a/server/mempool.py b/server/mempool.py
index 1a491e9..09b9fd7 100644
--- a/server/mempool.py
+++ b/server/mempool.py
@@ -27,9 +27,9 @@ class MemPool(util.LoggedClass):
     To that end we maintain the following maps:
 
        tx_hash -> (txin_pairs, txout_pairs)
-       hash168 -> set of all tx hashes in which the hash168 appears
+       hashX   -> set of all tx hashes in which the hashX appears
 
-    A pair is a (hash168, value) tuple.  tx hashes are hex strings.
+    A pair is a (hashX, value) tuple.  tx hashes are hex strings.
     '''
 
     def __init__(self, daemon, coin, db):
@@ -42,7 +42,7 @@ class MemPool(util.LoggedClass):
         self.prioritized = set()
         self.stop = False
         self.txs = {}
-        self.hash168s = defaultdict(set)  # None can be a key
+        self.hashXs = defaultdict(set)  # None can be a key
 
     def prioritize(self, tx_hash):
         '''Prioritize processing the given hash.  This is important during
@@ -56,7 +56,7 @@ class MemPool(util.LoggedClass):
         unfetched.  Add new ones to unprocessed.
         '''
         txs = self.txs
-        hash168s = self.hash168s
+        hashXs = self.hashXs
         touched = self.touched
 
         hashes = self.daemon.cached_mempool_hashes()
@@ -67,13 +67,13 @@ class MemPool(util.LoggedClass):
             item = txs.pop(hex_hash)
             if item:
                 txin_pairs, txout_pairs = item
-                tx_hash168s = set(hash168 for hash168, value in txin_pairs)
-                tx_hash168s.update(hash168 for hash168, value in txout_pairs)
-                for hash168 in tx_hash168s:
-                    hash168s[hash168].remove(hex_hash)
-                    if not hash168s[hash168]:
-                        del hash168s[hash168]
-                touched.update(tx_hash168s)
+                tx_hashXs = set(hashX for hashX, value in txin_pairs)
+                tx_hashXs.update(hashX for hashX, value in txout_pairs)
+                for hashX in tx_hashXs:
+                    hashXs[hashX].remove(hex_hash)
+                    if not hashXs[hashX]:
+                        del hashXs[hashX]
+                touched.update(tx_hashXs)
 
         new = hashes.difference(txs)
         unfetched.update(new)
@@ -114,7 +114,7 @@ class MemPool(util.LoggedClass):
                 now = time.time()
                 if now >= next_log and loops:
                     self.logger.info('{:,d} txs touching {:,d} addresses'
-                                     .format(len(txs), len(self.hash168s)))
+                                     .format(len(txs), len(self.hashXs)))
                     next_log = now + 150
 
             try:
@@ -168,14 +168,14 @@ class MemPool(util.LoggedClass):
             result, deferred = await loop.run_in_executor(None, job)
 
             pending.extend(deferred)
-            hash168s = self.hash168s
+            hashXs = self.hashXs
             touched = self.touched
             for hex_hash, in_out_pairs in result.items():
                 if hex_hash in txs:
                     txs[hex_hash] = in_out_pairs
-                    for hash168, value in itertools.chain(*in_out_pairs):
-                        touched.add(hash168)
-                        hash168s[hash168].add(hex_hash)
+                    for hashX, value in itertools.chain(*in_out_pairs):
+                        touched.add(hashX)
+                        hashXs[hashX].add(hex_hash)
 
         return process
 
@@ -199,7 +199,7 @@ class MemPool(util.LoggedClass):
         variables it doesn't own.  Atomic reads of self.txs that do
         not depend on the result remaining the same are fine.
         '''
-        script_hash168 = self.coin.hash168_from_script()
+        script_hashX = self.coin.hashX_from_script
         db_utxo_lookup = self.db.db_utxo_lookup
         txs = self.txs
 
@@ -209,8 +209,8 @@ class MemPool(util.LoggedClass):
                 continue
             tx = Deserializer(raw_tx).read_tx()
 
-            # Convert the tx outputs into (hash168, value) pairs
-            txout_pairs = [(script_hash168(txout.pk_script), txout.value)
+            # Convert the tx outputs into (hashX, value) pairs
+            txout_pairs = [(script_hashX(txout.pk_script), txout.value)
                            for txout in tx.outputs]
 
             # Convert the tx inputs to ([prev_hex_hash, prev_idx) pairs
@@ -261,17 +261,17 @@ class MemPool(util.LoggedClass):
 
         return result, deferred
 
-    async def transactions(self, hash168):
+    async def transactions(self, hashX):
         '''Generate (hex_hash, tx_fee, unconfirmed) tuples for mempool
-        entries for the hash168.
+        entries for the hashX.
 
         unconfirmed is True if any txin is unconfirmed.
         '''
-        # hash168s is a defaultdict
-        if not hash168 in self.hash168s:
+        # hashXs is a defaultdict
+        if not hashX in self.hashXs:
             return []
 
-        hex_hashes = self.hash168s[hash168]
+        hex_hashes = self.hashXs[hashX]
         raw_txs = await self.daemon.getrawtransactions(hex_hashes)
         result = []
         for hex_hash, raw_tx in zip(hex_hashes, raw_txs):
@@ -279,23 +279,23 @@ class MemPool(util.LoggedClass):
             if not item or not raw_tx:
                 continue
             txin_pairs, txout_pairs = item
-            tx_fee = (sum(v for hash168, v in txin_pairs)
-                      - sum(v for hash168, v in txout_pairs))
+            tx_fee = (sum(v for hashX, v in txin_pairs)
+                      - sum(v for hashX, v in txout_pairs))
             tx = Deserializer(raw_tx).read_tx()
             unconfirmed = any(txin.prev_hash in self.txs for txin in tx.inputs)
             result.append((hex_hash, tx_fee, unconfirmed))
         return result
 
-    def value(self, hash168):
-        '''Return the unconfirmed amount in the mempool for hash168.
+    def value(self, hashX):
+        '''Return the unconfirmed amount in the mempool for hashX.
 
         Can be positive or negative.
         '''
         value = 0
-        # hash168s is a defaultdict
-        if hash168 in self.hash168s:
-            for hex_hash in self.hash168s[hash168]:
+        # hashXs is a defaultdict
+        if hashX in self.hashXs:
+            for hex_hash in self.hashXs[hashX]:
                 txin_pairs, txout_pairs = self.txs[hex_hash]
-                value -= sum(v for h168, v in txin_pairs if h168 == hash168)
-                value += sum(v for h168, v in txout_pairs if h168 == hash168)
+                value -= sum(v for h168, v in txin_pairs if h168 == hashX)
+                value += sum(v for h168, v in txout_pairs if h168 == hashX)
         return value
diff --git a/server/protocol.py b/server/protocol.py
index bd3d783..1b0516f 100644
--- a/server/protocol.py
+++ b/server/protocol.py
@@ -14,6 +14,7 @@ import traceback
 
 from lib.hash import sha256, double_sha256, hash_to_str, hex_str_to_hash
 from lib.jsonrpc import JSONRPC
+from lib.tx import Deserializer
 from server.daemon import DaemonError
 from server.version import VERSION
 
@@ -138,17 +139,17 @@ class Session(JSONRPC):
         raise self.RPCError('parameter should be a transaction hash: {}'
                             .format(param))
 
-    def param_to_hash168(self, param):
+    def param_to_hashX(self, param):
         if isinstance(param, str):
             try:
-                return self.coin.address_to_hash168(param)
+                return self.coin.address_to_hashX(param)
             except:
                 pass
         raise self.RPCError('param {} is not a valid address'.format(param))
 
-    def params_to_hash168(self, params):
+    def params_to_hashX(self, params):
         if len(params) == 1:
-            return self.param_to_hash168(params[0])
+            return self.param_to_hashX(params[0])
         raise self.RPCError('params {} should contain a single address'
                             .format(params))
 
@@ -162,7 +163,7 @@ class ElectrumX(Session):
         self.subscribe_height = False
         self.notified_height = None
         self.max_subs = self.env.max_session_subs
-        self.hash168s = set()
+        self.hashX_subs = {}
         rpcs = [
             ('blockchain',
              'address.get_balance address.get_history address.get_mempool '
@@ -179,7 +180,7 @@ class ElectrumX(Session):
                          for suffix in suffixes.split()}
 
     def sub_count(self):
-        return len(self.hash168s)
+        return len(self.hashX_subs)
 
     async def notify(self, height, touched):
         '''Notify the client about changes in height and touched addresses.
@@ -202,11 +203,10 @@ class ElectrumX(Session):
                 )
                 self.encode_and_send_payload(payload)
 
-        hash168_to_address = self.coin.hash168_to_address
-        matches = self.hash168s.intersection(touched)
-        for hash168 in matches:
-            address = hash168_to_address(hash168)
-            status = await self.address_status(hash168)
+        matches = touched.intersection(self.hashX_subs)
+        for hashX in matches:
+            address = self.hashX_subs[hashX]
+            status = await self.address_status(hashX)
             payload = self.notification_payload(
                 'blockchain.address.subscribe', (address, status))
             self.encode_and_send_payload(payload)
@@ -222,12 +222,12 @@ class ElectrumX(Session):
         '''Used as response to a headers subscription request.'''
         return self.manager.electrum_header(self.height())
 
-    async def address_status(self, hash168):
+    async def address_status(self, hashX):
         '''Returns status as 32 bytes.'''
         # Note history is ordered and mempool unordered in electrum-server
         # For mempool, height is -1 if unconfirmed txins, otherwise 0
-        history = await self.manager.async_get_history(hash168)
-        mempool = await self.manager.mempool_transactions(hash168)
+        history = await self.manager.async_get_history(hashX)
+        mempool = await self.manager.mempool_transactions(hashX)
 
         status = ''.join('{}:{:d}:'.format(hash_to_str(tx_hash), height)
                          for tx_hash, height in history)
@@ -262,20 +262,20 @@ class ElectrumX(Session):
 
         return {"block_height": height, "merkle": merkle_branch, "pos": pos}
 
-    async def unconfirmed_history(self, hash168):
+    async def unconfirmed_history(self, hashX):
         # Note unconfirmed history is unordered in electrum-server
         # Height is -1 if unconfirmed txins, otherwise 0
-        mempool = await self.manager.mempool_transactions(hash168)
+        mempool = await self.manager.mempool_transactions(hashX)
         return [{'tx_hash': tx_hash, 'height': -unconfirmed, 'fee': fee}
                 for tx_hash, fee, unconfirmed in mempool]
 
-    async def get_history(self, hash168):
+    async def get_history(self, hashX):
         # Note history is ordered but unconfirmed is unordered in e-s
-        history = await self.manager.async_get_history(hash168)
+        history = await self.manager.async_get_history(hashX)
         conf = [{'tx_hash': hash_to_str(tx_hash), 'height': height}
                 for tx_hash, height in history]
 
-        return conf + await self.unconfirmed_history(hash168)
+        return conf + await self.unconfirmed_history(hashX)
 
     def get_chunk(self, index):
         '''Return header chunk as hex.  Index is a non-negative integer.'''
@@ -285,55 +285,55 @@ class ElectrumX(Session):
         count = min(next_height - start_height, chunk_size)
         return self.bp.read_headers(start_height, count).hex()
 
-    async def get_utxos(self, hash168):
+    async def get_utxos(self, hashX):
         '''Get UTXOs asynchronously to reduce latency.'''
         def job():
-            return list(self.bp.get_utxos(hash168, limit=None))
+            return list(self.bp.get_utxos(hashX, limit=None))
         loop = asyncio.get_event_loop()
         return await loop.run_in_executor(None, job)
 
-    async def get_balance(self, hash168):
-        utxos = await self.get_utxos(hash168)
+    async def get_balance(self, hashX):
+        utxos = await self.get_utxos(hashX)
         confirmed = sum(utxo.value for utxo in utxos)
-        unconfirmed = self.manager.mempool_value(hash168)
+        unconfirmed = self.manager.mempool_value(hashX)
         return {'confirmed': confirmed, 'unconfirmed': unconfirmed}
 
-    async def list_unspent(self, hash168):
+    async def list_unspent(self, hashX):
         return [{'tx_hash': hash_to_str(utxo.tx_hash), 'tx_pos': utxo.tx_pos,
                  'height': utxo.height, 'value': utxo.value}
-                for utxo in sorted(await self.get_utxos(hash168))]
+                for utxo in sorted(await self.get_utxos(hashX))]
 
     # --- blockchain commands
 
     async def address_get_balance(self, params):
-        hash168 = self.params_to_hash168(params)
-        return await self.get_balance(hash168)
+        hashX = self.params_to_hashX(params)
+        return await self.get_balance(hashX)
 
     async def address_get_history(self, params):
-        hash168 = self.params_to_hash168(params)
-        return await self.get_history(hash168)
+        hashX = self.params_to_hashX(params)
+        return await self.get_history(hashX)
 
     async def address_get_mempool(self, params):
-        hash168 = self.params_to_hash168(params)
-        return await self.unconfirmed_history(hash168)
+        hashX = self.params_to_hashX(params)
+        return await self.unconfirmed_history(hashX)
 
     async def address_get_proof(self, params):
-        hash168 = self.params_to_hash168(params)
+        hashX = self.params_to_hashX(params)
         raise self.RPCError('get_proof is not yet implemented')
 
     async def address_listunspent(self, params):
-        hash168 = self.params_to_hash168(params)
-        return await self.list_unspent(hash168)
+        hashX = self.params_to_hashX(params)
+        return await self.list_unspent(hashX)
 
     async def address_subscribe(self, params):
-        hash168 = self.params_to_hash168(params)
-        if len(self.hash168s) >= self.max_subs:
+        hashX = self.params_to_hashX(params)
+        if len(self.hashX_subs) >= self.max_subs:
             raise self.RPCError('your address subscription limit {:,d} reached'
                                 .format(self.max_subs))
-        result = await self.address_status(hash168)
+        result = await self.address_status(hashX)
         # add_subscription can raise so call it before adding
         self.manager.new_subscription()
-        self.hash168s.add(hash168)
+        self.hashX_subs[hashX] = params[0]
         return result
 
     async def block_get_chunk(self, params):
@@ -414,14 +414,23 @@ class ElectrumX(Session):
                             'and height')
 
     async def utxo_get_address(self, params):
+        '''Returns the address for a TXO.
+
+        Used only for electrum client command-line requests.  We no
+        longer index by address, so need to request the raw
+        transaction.  So it works for any TXO not just UTXOs.
+        '''
         if len(params) == 2:
             tx_hash = self.param_to_tx_hash(params[0])
             index = self.param_to_non_negative_integer(params[1])
-            tx_hash = hex_str_to_hash(tx_hash)
-            hash168 = self.bp.get_utxo_hash168(tx_hash, index)
-            if hash168:
-                return self.coin.hash168_to_address(hash168)
-            return None
+            raw_tx = await self.daemon_request('getrawtransaction', tx_hash)
+            if not raw_tx:
+                return None
+            raw_tx = bytes.fromhex(raw_tx)
+            tx = Deserializer(raw_tx).read_tx()
+            if index >= len(tx.outputs):
+                return None
+            return self.coin.address_from_script(tx.outputs[index].pk_script)
 
         raise self.RPCError('params should contain a transaction hash '
                             'and index')