713 lines
27 KiB
Python
713 lines
27 KiB
Python
# Copyright (c) 2016-2017, Neil Booth
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# Copyright (c) 2017, the ElectrumX authors
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#
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# All rights reserved.
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#
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# See the file "LICENCE" for information about the copyright
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# and warranty status of this software.
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'''Block prefetcher and chain processor.'''
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import array
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import asyncio
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from struct import pack, unpack
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import time
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from functools import partial
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from torba.rpc import TaskGroup, run_in_thread
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import torba
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from torba.server.daemon import DaemonError
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from torba.server.hash import hash_to_hex_str, HASHX_LEN
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from torba.server.util import chunks, class_logger
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from torba.server.db import FlushData
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class Prefetcher:
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'''Prefetches blocks (in the forward direction only).'''
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def __init__(self, daemon, coin, blocks_event):
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self.logger = class_logger(__name__, self.__class__.__name__)
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self.daemon = daemon
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self.coin = coin
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self.blocks_event = blocks_event
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self.blocks = []
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self.caught_up = False
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# Access to fetched_height should be protected by the semaphore
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self.fetched_height = None
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self.semaphore = asyncio.Semaphore()
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self.refill_event = asyncio.Event()
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# The prefetched block cache size. The min cache size has
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# little effect on sync time.
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self.cache_size = 0
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self.min_cache_size = 10 * 1024 * 1024
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# This makes the first fetch be 10 blocks
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self.ave_size = self.min_cache_size // 10
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self.polling_delay = 5
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async def main_loop(self, bp_height):
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'''Loop forever polling for more blocks.'''
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await self.reset_height(bp_height)
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while True:
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try:
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# Sleep a while if there is nothing to prefetch
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await self.refill_event.wait()
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if not await self._prefetch_blocks():
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await asyncio.sleep(self.polling_delay)
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except DaemonError as e:
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self.logger.info(f'ignoring daemon error: {e}')
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def get_prefetched_blocks(self):
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'''Called by block processor when it is processing queued blocks.'''
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blocks = self.blocks
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self.blocks = []
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self.cache_size = 0
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self.refill_event.set()
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return blocks
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async def reset_height(self, height):
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'''Reset to prefetch blocks from the block processor's height.
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Used in blockchain reorganisations. This coroutine can be
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called asynchronously to the _prefetch_blocks coroutine so we
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must synchronize with a semaphore.
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'''
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async with self.semaphore:
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self.blocks.clear()
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self.cache_size = 0
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self.fetched_height = height
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self.refill_event.set()
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daemon_height = await self.daemon.height()
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behind = daemon_height - height
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if behind > 0:
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self.logger.info('catching up to daemon height {:,d} '
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'({:,d} blocks behind)'
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.format(daemon_height, behind))
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else:
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self.logger.info('caught up to daemon height {:,d}'
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.format(daemon_height))
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async def _prefetch_blocks(self):
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'''Prefetch some blocks and put them on the queue.
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Repeats until the queue is full or caught up.
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'''
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daemon = self.daemon
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daemon_height = await daemon.height()
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async with self.semaphore:
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while self.cache_size < self.min_cache_size:
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# Try and catch up all blocks but limit to room in cache.
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# Constrain fetch count to between 0 and 500 regardless;
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# testnet can be lumpy.
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cache_room = self.min_cache_size // self.ave_size
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count = min(daemon_height - self.fetched_height, cache_room)
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count = min(500, max(count, 0))
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if not count:
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self.caught_up = True
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return False
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first = self.fetched_height + 1
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hex_hashes = await daemon.block_hex_hashes(first, count)
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if self.caught_up:
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self.logger.info('new block height {:,d} hash {}'
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.format(first + count-1, hex_hashes[-1]))
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blocks = await daemon.raw_blocks(hex_hashes)
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assert count == len(blocks)
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# Special handling for genesis block
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if first == 0:
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blocks[0] = self.coin.genesis_block(blocks[0])
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self.logger.info('verified genesis block with hash {}'
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.format(hex_hashes[0]))
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# Update our recent average block size estimate
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size = sum(len(block) for block in blocks)
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if count >= 10:
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self.ave_size = size // count
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else:
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self.ave_size = (size + (10 - count) * self.ave_size) // 10
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self.blocks.extend(blocks)
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self.cache_size += size
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self.fetched_height += count
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self.blocks_event.set()
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self.refill_event.clear()
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return True
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class ChainError(Exception):
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'''Raised on error processing blocks.'''
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class BlockProcessor:
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'''Process blocks and update the DB state to match.
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Employ a prefetcher to prefetch blocks in batches for processing.
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Coordinate backing up in case of chain reorganisations.
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'''
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def __init__(self, env, db, daemon, notifications):
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self.env = env
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self.db = db
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self.daemon = daemon
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self.notifications = notifications
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self.coin = env.coin
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self.blocks_event = asyncio.Event()
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self.prefetcher = Prefetcher(daemon, env.coin, self.blocks_event)
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self.logger = class_logger(__name__, self.__class__.__name__)
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# Meta
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self.next_cache_check = 0
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self.touched = set()
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self.reorg_count = 0
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# Caches of unflushed items.
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self.headers = []
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self.tx_hashes = []
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self.undo_infos = []
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# UTXO cache
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self.utxo_cache = {}
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self.db_deletes = []
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# If the lock is successfully acquired, in-memory chain state
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# is consistent with self.height
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self.state_lock = asyncio.Lock()
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async def run_in_thread_with_lock(self, func, *args):
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# Run in a thread to prevent blocking. Shielded so that
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# cancellations from shutdown don't lose work - when the task
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# completes the data will be flushed and then we shut down.
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# Take the state lock to be certain in-memory state is
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# consistent and not being updated elsewhere.
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async def run_in_thread_locked():
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async with self.state_lock:
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return await run_in_thread(func, *args)
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return await asyncio.shield(run_in_thread_locked())
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async def check_and_advance_blocks(self, raw_blocks):
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'''Process the list of raw blocks passed. Detects and handles
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reorgs.
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'''
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if not raw_blocks:
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return
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first = self.height + 1
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blocks = [self.coin.block(raw_block, first + n)
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for n, raw_block in enumerate(raw_blocks)]
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headers = [block.header for block in blocks]
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hprevs = [self.coin.header_prevhash(h) for h in headers]
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chain = [self.tip] + [self.coin.header_hash(h) for h in headers[:-1]]
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if hprevs == chain:
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start = time.time()
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await self.run_in_thread_with_lock(self.advance_blocks, blocks)
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await self._maybe_flush()
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if not self.db.first_sync:
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s = '' if len(blocks) == 1 else 's'
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self.logger.info('processed {:,d} block{} in {:.1f}s'
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.format(len(blocks), s,
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time.time() - start))
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if self._caught_up_event.is_set():
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await self.notifications.on_block(self.touched, self.height)
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self.touched = set()
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elif hprevs[0] != chain[0]:
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await self.reorg_chain()
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else:
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# It is probably possible but extremely rare that what
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# bitcoind returns doesn't form a chain because it
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# reorg-ed the chain as it was processing the batched
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# block hash requests. Should this happen it's simplest
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# just to reset the prefetcher and try again.
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self.logger.warning('daemon blocks do not form a chain; '
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'resetting the prefetcher')
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await self.prefetcher.reset_height(self.height)
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async def reorg_chain(self, count=None):
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'''Handle a chain reorganisation.
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Count is the number of blocks to simulate a reorg, or None for
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a real reorg.'''
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if count is None:
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self.logger.info('chain reorg detected')
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else:
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self.logger.info(f'faking a reorg of {count:,d} blocks')
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await self.flush(True)
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async def get_raw_blocks(last_height, hex_hashes):
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heights = range(last_height, last_height - len(hex_hashes), -1)
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try:
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blocks = [self.db.read_raw_block(height) for height in heights]
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self.logger.info(f'read {len(blocks)} blocks from disk')
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return blocks
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except FileNotFoundError:
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return await self.daemon.raw_blocks(hex_hashes)
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def flush_backup():
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# self.touched can include other addresses which is
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# harmless, but remove None.
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self.touched.discard(None)
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self.db.flush_backup(self.flush_data(), self.touched)
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start, last, hashes = await self.reorg_hashes(count)
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# Reverse and convert to hex strings.
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hashes = [hash_to_hex_str(hash) for hash in reversed(hashes)]
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for hex_hashes in chunks(hashes, 50):
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raw_blocks = await get_raw_blocks(last, hex_hashes)
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await self.run_in_thread_with_lock(self.backup_blocks, raw_blocks)
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await self.run_in_thread_with_lock(flush_backup)
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last -= len(raw_blocks)
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await self.prefetcher.reset_height(self.height)
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async def reorg_hashes(self, count):
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'''Return a pair (start, last, hashes) of blocks to back up during a
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reorg.
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The hashes are returned in order of increasing height. Start
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is the height of the first hash, last of the last.
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'''
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start, count = await self.calc_reorg_range(count)
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last = start + count - 1
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s = '' if count == 1 else 's'
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self.logger.info(f'chain was reorganised replacing {count:,d} '
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f'block{s} at heights {start:,d}-{last:,d}')
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return start, last, await self.db.fs_block_hashes(start, count)
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async def calc_reorg_range(self, count):
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'''Calculate the reorg range'''
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def diff_pos(hashes1, hashes2):
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'''Returns the index of the first difference in the hash lists.
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If both lists match returns their length.'''
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for n, (hash1, hash2) in enumerate(zip(hashes1, hashes2)):
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if hash1 != hash2:
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return n
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return len(hashes)
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if count is None:
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# A real reorg
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start = self.height - 1
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count = 1
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while start > 0:
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hashes = await self.db.fs_block_hashes(start, count)
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hex_hashes = [hash_to_hex_str(hash) for hash in hashes]
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d_hex_hashes = await self.daemon.block_hex_hashes(start, count)
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n = diff_pos(hex_hashes, d_hex_hashes)
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if n > 0:
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start += n
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break
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count = min(count * 2, start)
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start -= count
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count = (self.height - start) + 1
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else:
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start = (self.height - count) + 1
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return start, count
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def estimate_txs_remaining(self):
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# Try to estimate how many txs there are to go
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daemon_height = self.daemon.cached_height()
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coin = self.coin
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tail_count = daemon_height - max(self.height, coin.TX_COUNT_HEIGHT)
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# Damp the initial enthusiasm
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realism = max(2.0 - 0.9 * self.height / coin.TX_COUNT_HEIGHT, 1.0)
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return (tail_count * coin.TX_PER_BLOCK +
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max(coin.TX_COUNT - self.tx_count, 0)) * realism
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# - Flushing
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def flush_data(self):
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'''The data for a flush. The lock must be taken.'''
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assert self.state_lock.locked()
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return FlushData(self.height, self.tx_count, self.headers,
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self.tx_hashes, self.undo_infos, self.utxo_cache,
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self.db_deletes, self.tip)
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async def flush(self, flush_utxos):
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def flush():
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self.db.flush_dbs(self.flush_data(), flush_utxos,
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self.estimate_txs_remaining)
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await self.run_in_thread_with_lock(flush)
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async def _maybe_flush(self):
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# If caught up, flush everything as client queries are
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# performed on the DB.
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if self._caught_up_event.is_set():
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await self.flush(True)
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elif time.time() > self.next_cache_check:
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flush_arg = self.check_cache_size()
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if flush_arg is not None:
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await self.flush(flush_arg)
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self.next_cache_check = time.time() + 30
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def check_cache_size(self):
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'''Flush a cache if it gets too big.'''
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# Good average estimates based on traversal of subobjects and
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# requesting size from Python (see deep_getsizeof).
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one_MB = 1000*1000
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utxo_cache_size = len(self.utxo_cache) * 205
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db_deletes_size = len(self.db_deletes) * 57
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hist_cache_size = self.db.history.unflushed_memsize()
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# Roughly ntxs * 32 + nblocks * 42
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tx_hash_size = ((self.tx_count - self.db.fs_tx_count) * 32
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+ (self.height - self.db.fs_height) * 42)
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utxo_MB = (db_deletes_size + utxo_cache_size) // one_MB
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hist_MB = (hist_cache_size + tx_hash_size) // one_MB
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self.logger.info('our height: {:,d} daemon: {:,d} '
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'UTXOs {:,d}MB hist {:,d}MB'
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.format(self.height, self.daemon.cached_height(),
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utxo_MB, hist_MB))
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# Flush history if it takes up over 20% of cache memory.
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# Flush UTXOs once they take up 80% of cache memory.
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cache_MB = self.env.cache_MB
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if utxo_MB + hist_MB >= cache_MB or hist_MB >= cache_MB // 5:
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return utxo_MB >= cache_MB * 4 // 5
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return None
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def advance_blocks(self, blocks):
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'''Synchronously advance the blocks.
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It is already verified they correctly connect onto our tip.
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'''
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min_height = self.db.min_undo_height(self.daemon.cached_height())
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height = self.height
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for block in blocks:
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height += 1
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undo_info = self.advance_txs(block.transactions)
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if height >= min_height:
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self.undo_infos.append((undo_info, height))
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self.db.write_raw_block(block.raw, height)
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headers = [block.header for block in blocks]
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self.height = height
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self.headers.extend(headers)
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self.tip = self.coin.header_hash(headers[-1])
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def advance_txs(self, txs):
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self.tx_hashes.append(b''.join(tx_hash for tx, tx_hash in txs))
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# Use local vars for speed in the loops
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undo_info = []
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tx_num = self.tx_count
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script_hashX = self.coin.hashX_from_script
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s_pack = pack
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put_utxo = self.utxo_cache.__setitem__
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spend_utxo = self.spend_utxo
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undo_info_append = undo_info.append
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update_touched = self.touched.update
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hashXs_by_tx = []
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append_hashXs = hashXs_by_tx.append
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for tx, tx_hash in txs:
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hashXs = []
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append_hashX = hashXs.append
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tx_numb = s_pack('<I', tx_num)
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# Spend the inputs
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for txin in tx.inputs:
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if txin.is_generation():
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continue
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cache_value = spend_utxo(txin.prev_hash, txin.prev_idx)
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undo_info_append(cache_value)
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append_hashX(cache_value[:-12])
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# Add the new UTXOs
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for idx, txout in enumerate(tx.outputs):
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# Get the hashX. Ignore unspendable outputs
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hashX = script_hashX(txout.pk_script)
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if hashX:
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append_hashX(hashX)
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put_utxo(tx_hash + s_pack('<H', idx),
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hashX + tx_numb + s_pack('<Q', txout.value))
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append_hashXs(hashXs)
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update_touched(hashXs)
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tx_num += 1
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self.db.history.add_unflushed(hashXs_by_tx, self.tx_count)
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self.tx_count = tx_num
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self.db.tx_counts.append(tx_num)
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return undo_info
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def backup_blocks(self, raw_blocks):
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'''Backup the raw blocks and flush.
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The blocks should be in order of decreasing height, starting at.
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self.height. A flush is performed once the blocks are backed up.
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'''
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self.db.assert_flushed(self.flush_data())
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assert self.height >= len(raw_blocks)
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coin = self.coin
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for raw_block in raw_blocks:
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# Check and update self.tip
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block = coin.block(raw_block, self.height)
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header_hash = coin.header_hash(block.header)
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if header_hash != self.tip:
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raise ChainError('backup block {} not tip {} at height {:,d}'
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.format(hash_to_hex_str(header_hash),
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hash_to_hex_str(self.tip),
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self.height))
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self.tip = coin.header_prevhash(block.header)
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self.backup_txs(block.transactions)
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self.height -= 1
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self.db.tx_counts.pop()
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self.logger.info('backed up to height {:,d}'.format(self.height))
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def backup_txs(self, txs):
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# Prevout values, in order down the block (coinbase first if present)
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# undo_info is in reverse block order
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undo_info = self.db.read_undo_info(self.height)
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if undo_info is None:
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raise ChainError('no undo information found for height {:,d}'
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.format(self.height))
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n = len(undo_info)
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# Use local vars for speed in the loops
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s_pack = pack
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put_utxo = self.utxo_cache.__setitem__
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spend_utxo = self.spend_utxo
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script_hashX = self.coin.hashX_from_script
|
|
touched = self.touched
|
|
undo_entry_len = 12 + HASHX_LEN
|
|
|
|
for tx, tx_hash in reversed(txs):
|
|
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.
|
|
hashX = script_hashX(txout.pk_script)
|
|
if hashX:
|
|
cache_value = spend_utxo(tx_hash, idx)
|
|
touched.add(cache_value[:-12])
|
|
|
|
# Restore the inputs
|
|
for txin in reversed(tx.inputs):
|
|
if txin.is_generation():
|
|
continue
|
|
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[:-12])
|
|
|
|
assert n == 0
|
|
self.tx_count -= len(txs)
|
|
|
|
'''An in-memory UTXO cache, representing all changes to UTXO state
|
|
since the last DB flush.
|
|
|
|
We want to store millions of these in memory for optimal
|
|
performance during initial sync, because then it is possible to
|
|
spend UTXOs without ever going to the database (other than as an
|
|
entry in the address history, and there is only one such entry per
|
|
TX not per UTXO). So store them in a Python dictionary with
|
|
binary keys and values.
|
|
|
|
Key: TX_HASH + TX_IDX (32 + 2 = 34 bytes)
|
|
Value: HASHX + TX_NUM + VALUE (11 + 4 + 8 = 23 bytes)
|
|
|
|
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:
|
|
|
|
add: Add it to the cache dictionary.
|
|
|
|
spend: Remove it if in the cache dictionary. Otherwise it's
|
|
been flushed to the DB. Each UTXO is responsible for two
|
|
entries in the DB. Mark them for deletion in the next
|
|
cache flush.
|
|
|
|
The UTXO database format has to be able to do two things efficiently:
|
|
|
|
1. Given an address be able to list its UTXOs and their values
|
|
so its balance can be efficiently computed.
|
|
|
|
2. When processing transactions, for each prevout spent - a (tx_hash,
|
|
idx) pair - we have to be able to remove it from the DB. To send
|
|
notifications to clients we also need to know any address it paid
|
|
to.
|
|
|
|
To this end we maintain two "tables", one for each point above:
|
|
|
|
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: 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
|
|
will be potential collisions so tx_num is also in the key. When
|
|
looking up a UTXO the prefix space of the compressed hash needs to
|
|
be searched and resolved if necessary with the tx_num. The
|
|
collision rate is low (<0.1%).
|
|
'''
|
|
|
|
def spend_utxo(self, tx_hash, tx_idx):
|
|
'''Spend a UTXO and return the 33-byte value.
|
|
|
|
If the UTXO is not in the cache it must be on disk. We store
|
|
all UTXOs so not finding one indicates a logic error or DB
|
|
corruption.
|
|
'''
|
|
# Fast track is it being in the cache
|
|
idx_packed = pack('<H', tx_idx)
|
|
cache_value = self.utxo_cache.pop(tx_hash + idx_packed, None)
|
|
if cache_value:
|
|
return cache_value
|
|
|
|
# Spend it from the DB.
|
|
|
|
# Key: b'h' + compressed_tx_hash + tx_idx + tx_num
|
|
# 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)}
|
|
|
|
for hdb_key, hashX in candidates.items():
|
|
tx_num_packed = hdb_key[-4:]
|
|
|
|
if len(candidates) > 1:
|
|
tx_num, = unpack('<I', tx_num_packed)
|
|
hash, height = self.db.fs_tx_hash(tx_num)
|
|
if hash != tx_hash:
|
|
assert hash is not None # Should always be found
|
|
continue
|
|
|
|
# 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)
|
|
if utxo_value_packed:
|
|
# 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
|
|
|
|
raise ChainError('UTXO {} / {:,d} not found in "h" table'
|
|
.format(hash_to_hex_str(tx_hash), tx_idx))
|
|
|
|
async def _process_prefetched_blocks(self):
|
|
'''Loop forever processing blocks as they arrive.'''
|
|
while True:
|
|
if self.height == self.daemon.cached_height():
|
|
if not self._caught_up_event.is_set():
|
|
await self._first_caught_up()
|
|
self._caught_up_event.set()
|
|
await self.blocks_event.wait()
|
|
self.blocks_event.clear()
|
|
if self.reorg_count:
|
|
await self.reorg_chain(self.reorg_count)
|
|
self.reorg_count = 0
|
|
else:
|
|
blocks = self.prefetcher.get_prefetched_blocks()
|
|
await self.check_and_advance_blocks(blocks)
|
|
|
|
async def _first_caught_up(self):
|
|
self.logger.info(f'caught up to height {self.height}')
|
|
# Flush everything but with first_sync->False state.
|
|
first_sync = self.db.first_sync
|
|
self.db.first_sync = False
|
|
await self.flush(True)
|
|
if first_sync:
|
|
self.logger.info(f'{torba.__version__} synced to '
|
|
f'height {self.height:,d}')
|
|
# Reopen for serving
|
|
await self.db.open_for_serving()
|
|
|
|
async def _first_open_dbs(self):
|
|
await self.db.open_for_sync()
|
|
self.height = self.db.db_height
|
|
self.tip = self.db.db_tip
|
|
self.tx_count = self.db.db_tx_count
|
|
|
|
# --- External API
|
|
|
|
async def fetch_and_process_blocks(self, caught_up_event):
|
|
'''Fetch, process and index blocks from the daemon.
|
|
|
|
Sets caught_up_event when first caught up. Flushes to disk
|
|
and shuts down cleanly if cancelled.
|
|
|
|
This is mainly because if, during initial sync ElectrumX is
|
|
asked to shut down when a large number of blocks have been
|
|
processed but not written to disk, it should write those to
|
|
disk before exiting, as otherwise a significant amount of work
|
|
could be lost.
|
|
'''
|
|
self._caught_up_event = caught_up_event
|
|
await self._first_open_dbs()
|
|
try:
|
|
async with TaskGroup() as group:
|
|
await group.spawn(self.prefetcher.main_loop(self.height))
|
|
await group.spawn(self._process_prefetched_blocks())
|
|
finally:
|
|
# Shut down block processing
|
|
self.logger.info('flushing to DB for a clean shutdown...')
|
|
await self.flush(True)
|
|
|
|
def force_chain_reorg(self, count):
|
|
'''Force a reorg of the given number of blocks.
|
|
|
|
Returns True if a reorg is queued, false if not caught up.
|
|
'''
|
|
if self._caught_up_event.is_set():
|
|
self.reorg_count = count
|
|
self.blocks_event.set()
|
|
return True
|
|
return False
|
|
|
|
|
|
class DecredBlockProcessor(BlockProcessor):
|
|
async def calc_reorg_range(self, count):
|
|
start, count = await super().calc_reorg_range(count)
|
|
if start > 0:
|
|
# A reorg in Decred can invalidate the previous block
|
|
start -= 1
|
|
count += 1
|
|
return start, count
|
|
|
|
|
|
class NamecoinBlockProcessor(BlockProcessor):
|
|
def advance_txs(self, txs):
|
|
result = super().advance_txs(txs)
|
|
|
|
tx_num = self.tx_count - len(txs)
|
|
script_name_hashX = self.coin.name_hashX_from_script
|
|
update_touched = self.touched.update
|
|
hashXs_by_tx = []
|
|
append_hashXs = hashXs_by_tx.append
|
|
|
|
for tx, tx_hash in txs:
|
|
hashXs = []
|
|
append_hashX = hashXs.append
|
|
|
|
# Add the new UTXOs and associate them with the name script
|
|
for idx, txout in enumerate(tx.outputs):
|
|
# Get the hashX of the name script. Ignore non-name scripts.
|
|
hashX = script_name_hashX(txout.pk_script)
|
|
if hashX:
|
|
append_hashX(hashX)
|
|
|
|
append_hashXs(hashXs)
|
|
update_touched(hashXs)
|
|
tx_num += 1
|
|
|
|
self.db.history.add_unflushed(hashXs_by_tx, self.tx_count - len(txs))
|
|
|
|
return result
|