Merge pull request #9926 from SomberNight/202506_iface_headers3

interface: faster chain resolution: add headers_cache

electrum/blockchain.py

@@ -445,7 +445,7 @@ class Blockchain(Logger):
             raise FileNotFoundError('Cannot find headers file but headers_dir is there. Should be at {}'.format(path))
 
     @with_lock
-    def write(self, data: bytes, offset: int, truncate: bool=True) -> None:
+    def write(self, data: bytes, offset: int, truncate: bool = True, *, fsync: bool = True) -> None:
         filename = self.path()
         self.assert_headers_file_available(filename)
         with open(filename, 'rb+') as f:
@@ -454,8 +454,9 @@ class Blockchain(Logger):
                 f.truncate()
             f.seek(offset)
             f.write(data)
-            f.flush()
-            os.fsync(f.fileno())
+            if fsync:
+                f.flush()
+                os.fsync(f.fileno())
         self.update_size()
 
     @with_lock
@@ -465,7 +466,8 @@ class Blockchain(Logger):
         # headers are only _appended_ to the end:
         assert delta == self.size(), (delta, self.size())
         assert len(data) == HEADER_SIZE
-        self.write(data, delta*HEADER_SIZE)
+        # note: we don't fsync, to improve perf. losing headers at end of file is ok.
+        self.write(data, delta*HEADER_SIZE, fsync=False)
         self.swap_with_parent()
 
     @with_lock

electrum/interface.py

@@ -525,6 +525,8 @@ class Interface(Logger):
         self.tip_header = None  # type: Optional[dict]
         self.tip = 0
 
+        self._headers_cache = {}  # type: Dict[int, bytes]
+
         self.fee_estimates_eta = {}  # type: Dict[int, int]
 
         # Dump network messages (only for this interface).  Set at runtime from the console.
@@ -756,16 +758,41 @@ class Interface(Logger):
             raise ErrorSSLCertFingerprintMismatch('Refusing to connect to server due to cert fingerprint mismatch')
         self.logger.info("cert fingerprint verification passed")
 
+    async def _maybe_warm_headers_cache(self, *, from_height: int, to_height: int, mode: ChainResolutionMode) -> None:
+        """Populate header cache for block heights in range [from_height, to_height]."""
+        assert from_height <= to_height, (from_height, to_height)
+        assert to_height - from_height < MAX_NUM_HEADERS_PER_REQUEST
+        if all(height in self._headers_cache for height in range(from_height, to_height+1)):
+            # cache already has all requested headers
+            return
+        # use lower timeout as we usually have network.bhi_lock here
+        timeout = self.network.get_network_timeout_seconds(NetworkTimeout.Urgent)
+        count = to_height - from_height + 1
+        headers = await self.get_block_headers(start_height=from_height, count=count, timeout=timeout, mode=mode)
+        for idx, raw_header in enumerate(headers):
+            header_height = from_height + idx
+            self._headers_cache[header_height] = raw_header
+
     async def get_block_header(self, height: int, *, mode: ChainResolutionMode) -> dict:
         if not is_non_negative_integer(height):
             raise Exception(f"{repr(height)} is not a block height")
-        self.logger.info(f'requesting block header {height} in {mode=}')
+        #self.logger.debug(f'get_block_header() {height} in {mode=}')
         # use lower timeout as we usually have network.bhi_lock here
         timeout = self.network.get_network_timeout_seconds(NetworkTimeout.Urgent)
+        if raw_header := self._headers_cache.get(height):
+            return blockchain.deserialize_header(raw_header, height)
+        self.logger.info(f'requesting block header {height} in {mode=}')
         res = await self.session.send_request('blockchain.block.header', [height], timeout=timeout)
         return blockchain.deserialize_header(bytes.fromhex(res), height)
 
-    async def get_block_headers(self, *, start_height: int, count: int) -> Sequence[bytes]:
+    async def get_block_headers(
+        self,
+        *,
+        start_height: int,
+        count: int,
+        timeout=None,
+        mode: Optional[ChainResolutionMode] = None,
+    ) -> Sequence[bytes]:
         """Request a number of consecutive block headers, starting at `start_height`.
         `count` is the num of requested headers, BUT note the server might return fewer than this
         (if range would extend beyond its tip).
@@ -775,8 +802,11 @@ class Interface(Logger):
             raise Exception(f"{repr(start_height)} is not a block height")
         if not is_non_negative_integer(count) or not (0 < count <= MAX_NUM_HEADERS_PER_REQUEST):
             raise Exception(f"{repr(count)} not an int in range ]0, {MAX_NUM_HEADERS_PER_REQUEST}]")
-        self.logger.info(f'requesting block headers: [{start_height}, {start_height+count-1}], {count=}')
-        res = await self.session.send_request('blockchain.block.headers', [start_height, count])
+        self.logger.info(
+            f"requesting block headers: [{start_height}, {start_height+count-1}], {count=}"
+            + (f" (in {mode=})" if mode is not None else "")
+        )
+        res = await self.session.send_request('blockchain.block.headers', [start_height, count], timeout=timeout)
         # check response
         assert_dict_contains_field(res, field_name='count')
         assert_dict_contains_field(res, field_name='hex')
@@ -938,17 +968,23 @@ class Interface(Logger):
             item = await header_queue.get()
             raw_header = item[0]
             height = raw_header['height']
-            header = blockchain.deserialize_header(bfh(raw_header['hex']), height)
-            self.tip_header = header
+            header_bytes = bfh(raw_header['hex'])
+            header_dict = blockchain.deserialize_header(header_bytes, height)
+            self.tip_header = header_dict
             self.tip = height
             if self.tip < constants.net.max_checkpoint():
                 raise GracefulDisconnect(
                     f"server tip below max checkpoint. ({self.tip} < {constants.net.max_checkpoint()})")
             self._mark_ready()
-            blockchain_updated = await self._process_header_at_tip()
+            self._headers_cache.clear()  # tip changed, so assume anything could have happened with chain
+            self._headers_cache[height] = header_bytes
+            try:
+                blockchain_updated = await self._process_header_at_tip()
+            finally:
+                self._headers_cache.clear()  # to reduce memory usage
             # header processing done
-            if self.is_main_server():
-                self.logger.info(f"new chain tip on main interface. {height=}")
+            if self.is_main_server() or blockchain_updated:
+                self.logger.info(f"new chain tip. {height=}")
             if blockchain_updated:
                 util.trigger_callback('blockchain_updated')
             util.trigger_callback('network_updated')
@@ -966,36 +1002,40 @@ class Interface(Logger):
             if self.blockchain.height() >= height and self.blockchain.check_header(header):
                 # another interface amended the blockchain
                 return False
-            _, height = await self.step(height, header=header)
-            # in the simple case, height == self.tip+1
-            if height <= self.tip:
-                await self.sync_until(height)
+            await self.sync_until(height)
             return True
 
     async def sync_until(
         self,
         height: int,
         *,
-        next_height: Optional[int] = None,
+        next_height: Optional[int] = None,  # sync target. typically the tip, except in unit tests
     ) -> Tuple[ChainResolutionMode, int]:
         if next_height is None:
             next_height = self.tip
         last = None  # type: Optional[ChainResolutionMode]
         while last is None or height <= next_height:
             prev_last, prev_height = last, height
-            if next_height > height + 10:  # TODO make smarter. the protocol allows asking for n headers
+            if next_height > height + 144:
+                # We are far from the tip.
+                # It is more efficient to process headers in large batches (CPU/disk_usage/logging).
+                # (but this wastes a little bandwidth, if we are not on a chunk boundary)
+                # TODO we should request (some) chunks concurrently. would help when we are many chunks behind
                 could_connect, num_headers = await self.request_chunk(height, tip=next_height)
                 if not could_connect:
                     if height <= constants.net.max_checkpoint():
                         raise GracefulDisconnect('server chain conflicts with checkpoints or genesis')
                     last, height = await self.step(height)
                     continue
+                # report progress to gui/etc
                 util.trigger_callback('blockchain_updated')
                 util.trigger_callback('network_updated')
                 height = (height // CHUNK_SIZE * CHUNK_SIZE) + num_headers
                 assert height <= next_height+1, (height, self.tip)
                 last = ChainResolutionMode.CATCHUP
             else:
+                # We are close to the tip, so process headers one-by-one.
+                # (note: due to headers_cache, to save network latency, this can still batch-request headers)
                 last, height = await self.step(height)
             assert (prev_last, prev_height) != (last, height), 'had to prevent infinite loop in interface.sync_until'
         return last, height
@@ -1003,12 +1043,14 @@ class Interface(Logger):
     async def step(
         self,
         height: int,
-        *,
-        header: Optional[dict] = None,  # at 'height'
     ) -> Tuple[ChainResolutionMode, int]:
         assert 0 <= height <= self.tip, (height, self.tip)
-        if header is None:
-            header = await self.get_block_header(height, mode=ChainResolutionMode.CATCHUP)
+        await self._maybe_warm_headers_cache(
+            from_height=height,
+            to_height=min(self.tip, height+MAX_NUM_HEADERS_PER_REQUEST-1),
+            mode=ChainResolutionMode.CATCHUP,
+        )
+        header = await self.get_block_header(height, mode=ChainResolutionMode.CATCHUP)
 
         chain = blockchain.check_header(header) if 'mock' not in header else header['mock']['check'](header)
         if chain:
@@ -1027,7 +1069,6 @@ class Interface(Logger):
             can_connect = blockchain.can_connect(header) if 'mock' not in header else header['mock']['connect'](height)
             assert chain or can_connect
         if can_connect:
-            self.logger.info(f"new block: {height=}")
             height += 1
             if isinstance(can_connect, Blockchain):  # not when mocking
                 self.blockchain = can_connect
@@ -1050,9 +1091,12 @@ class Interface(Logger):
         self.blockchain = chain if isinstance(chain, Blockchain) else self.blockchain
         good = height
         while True:
-            assert good < bad, (good, bad)
+            assert 0 <= good < bad, (good, bad)
             height = (good + bad) // 2
             self.logger.info(f"binary step. good {good}, bad {bad}, height {height}")
+            if bad - good + 1 <= MAX_NUM_HEADERS_PER_REQUEST:  # if interval is small, trade some bandwidth for lower latency
+                await self._maybe_warm_headers_cache(
+                    from_height=good, to_height=bad, mode=ChainResolutionMode.BINARY)
             header = await self.get_block_header(height, mode=ChainResolutionMode.BINARY)
             chain = blockchain.check_header(header) if 'mock' not in header else header['mock']['check'](header)
             if chain:
@@ -1127,9 +1171,14 @@ class Interface(Logger):
         with blockchain.blockchains_lock: chains = list(blockchain.blockchains.values())
         local_max = max([0] + [x.height() for x in chains]) if 'mock' not in header else float('inf')
         height = min(local_max + 1, height - 1)
+        assert height >= 0
+
+        await self._maybe_warm_headers_cache(
+            from_height=max(0, height-10), to_height=height, mode=ChainResolutionMode.BACKWARD)
+
         while await iterate():
             bad, bad_header = height, header
-            delta = self.tip - height
+            delta = self.tip - height  # FIXME why compared to tip? would be easier to cache if delta started at 1
             assert delta > 0, delta
             height = self.tip - 2 * delta
 

tests/test_network.py

@@ -46,6 +46,9 @@ class MockInterface(Interface):
     async def run(self):
         return
 
+    async def _maybe_warm_headers_cache(self, *args, **kwargs):
+        return
+
 
 class TestNetwork(ElectrumTestCase):