175 lines
6.9 KiB
Python
175 lines
6.9 KiB
Python
import logging
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import random
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from bintrees import RBTree
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from threading import Event
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logger = logging.getLogger(__name__)
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logger.setLevel(logging.INFO)
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class NoAvailableKeysError(ValueError):
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pass
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class CompletedKeys(object):
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def __init__(self, max_index, min_index=0):
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self._max_index = max_index
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self._min_index = min_index
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self.num_remaining = max_index - min_index
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self._slabs = RBTree()
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def _get_previous_or_none(self, index):
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try:
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return self._slabs.floor_item(index)
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except KeyError:
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return None
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def is_available(self, index):
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logger.debug('Testing index %s', index)
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if index >= self._max_index or index < self._min_index:
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logger.debug('Index out of range')
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return False
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try:
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prev_start, prev_length = self._slabs.floor_item(index)
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logger.debug('Prev range: %s-%s', prev_start, prev_start + prev_length)
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return (prev_start + prev_length) <= index
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except KeyError:
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return True
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def mark_completed(self, start_index, past_last_index):
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logger.debug('Marking the range completed: %s-%s', start_index, past_last_index)
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num_completed = min(past_last_index, self._max_index) - max(start_index, self._min_index)
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# Find the item directly before this and see if there is overlap
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to_discard = set()
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try:
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prev_start, prev_length = self._slabs.floor_item(start_index)
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max_prev_completed = prev_start + prev_length
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if max_prev_completed >= start_index:
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# we are going to merge with the range before us
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logger.debug('Merging with the prev range: %s-%s', prev_start, prev_start + prev_length)
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to_discard.add(prev_start)
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num_completed = max(num_completed - (max_prev_completed - start_index), 0)
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start_index = prev_start
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past_last_index = max(past_last_index, prev_start + prev_length)
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except KeyError:
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pass
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# Find all keys between the start and last index and merge them into one block
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for merge_start, merge_length in self._slabs.iter_items(start_index, past_last_index + 1):
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if merge_start in to_discard:
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logger.debug('Already merged with block %s-%s', merge_start, merge_start + merge_length)
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continue
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candidate_next_index = merge_start + merge_length
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logger.debug('Merging with block %s-%s', merge_start, candidate_next_index)
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num_completed -= merge_length - max(candidate_next_index - past_last_index, 0)
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to_discard.add(merge_start)
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past_last_index = max(past_last_index, candidate_next_index)
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# write the new block which is fully merged
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discard = False
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if past_last_index >= self._max_index:
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logger.debug('Discarding block and setting new max to: %s', start_index)
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self._max_index = start_index
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discard = True
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if start_index <= self._min_index:
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logger.debug('Discarding block and setting new min to: %s', past_last_index)
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self._min_index = past_last_index
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discard = True
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if to_discard:
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logger.debug('Discarding %s obsolete blocks', len(to_discard))
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self._slabs.remove_items(to_discard)
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if not discard:
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logger.debug('Writing new block with range: %s-%s', start_index, past_last_index)
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self._slabs.insert(start_index, past_last_index - start_index)
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# Update the number of remaining items with the adjustments we've made
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assert num_completed >= 0
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self.num_remaining -= num_completed
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logger.debug('Total blocks: %s', len(self._slabs))
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def get_block_start_index(self, block_size_estimate):
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logger.debug('Total range: %s-%s', self._min_index, self._max_index)
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if self._max_index <= self._min_index:
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raise NoAvailableKeysError('All indexes have been marked completed')
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num_holes = len(self._slabs) + 1
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random_hole = random.randint(0, num_holes - 1)
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logger.debug('Selected random hole %s with %s total holes', random_hole, num_holes)
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hole_start = self._min_index
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past_hole_end = self._max_index
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# Now that we have picked a hole, we need to define the bounds
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if random_hole > 0:
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# There will be a slab before this hole, find where it ends
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bound_entries = self._slabs.nsmallest(random_hole + 1)[-2:]
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left_index, left_len = bound_entries[0]
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logger.debug('Left range %s-%s', left_index, left_index + left_len)
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hole_start = left_index + left_len
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if len(bound_entries) > 1:
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right_index, right_len = bound_entries[1]
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logger.debug('Right range %s-%s', right_index, right_index + right_len)
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past_hole_end, _ = bound_entries[1]
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elif not self._slabs.is_empty():
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right_index, right_len = self._slabs.nsmallest(1)[0]
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logger.debug('Right range %s-%s', right_index, right_index + right_len)
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past_hole_end, _ = self._slabs.nsmallest(1)[0]
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# Now that we have our hole bounds, select a random block from [0:len - block_size_estimate]
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logger.debug('Selecting from hole range: %s-%s', hole_start, past_hole_end)
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rand_max_bound = max(hole_start, past_hole_end - block_size_estimate)
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logger.debug('Rand max bound: %s', rand_max_bound)
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return random.randint(hole_start, rand_max_bound)
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def yield_random_entries(batch_query, primary_key_field, batch_size, max_id, min_id=0):
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""" This method will yield items from random blocks in the database. We will track metadata
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about which keys are available for work, and we will complete the backfill when there is no
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more work to be done. The method yields tuples of (candidate, Event), and if the work was
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already done by another worker, the caller should set the event. Batch candidates must have
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an "id" field which can be inspected.
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"""
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min_id = max(min_id, 0)
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max_id = max(max_id, 1)
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allocator = CompletedKeys(max_id + 1, min_id)
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try:
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while True:
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start_index = allocator.get_block_start_index(batch_size)
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end_index = min(start_index + batch_size, max_id + 1)
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all_candidates = list(batch_query()
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.where(primary_key_field >= start_index,
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primary_key_field < end_index)
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.order_by(primary_key_field))
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if len(all_candidates) == 0:
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logger.info('No candidates, marking entire block completed %s-%s', start_index, end_index)
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allocator.mark_completed(start_index, end_index)
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continue
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logger.info('Found %s candidates, processing block', len(all_candidates))
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batch_completed = 0
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for candidate in all_candidates:
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abort_early = Event()
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yield candidate, abort_early, allocator.num_remaining - batch_completed
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batch_completed += 1
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if abort_early.is_set():
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logger.info('Overlap with another worker, aborting')
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break
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completed_through = candidate.id + 1
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logger.info('Marking id range as completed: %s-%s', start_index, completed_through)
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allocator.mark_completed(start_index, completed_through)
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except NoAvailableKeysError:
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logger.info('No more work')
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