Optimize the ring builder's _reassign_parts() method.
Another ring builder optimization. Profiling revealed hotspots in many calls to min() and list.sort() in _reassign_parts(). That method didn't get exercised in my last optimization pass because that pass targeted a rebalance where nothing really moved around. This time, I wrote a script which created a fresh ring, added a bunch of devices, did the initial balance, deleted some devices, balanced, and added some more back in. Results from homebrew Python 2.7.3 on OS X 10.8.2 Macbook Pro (bare-metal): BEFORE: Using part-power = 18, adding 600 devices, removing 100, then adding 300 more... NOT Profiling to 'initial_balance.prof' wall-time delta: 131.33s NOT Profiling to 'deleting_200_rebalance.prof' wall-time delta: 25.67s NOT Profiling to 'first_rebalance.prof' wall-time delta: 62.00s AFTER: Using part-power = 18, adding 600 devices, removing 100, then adding 300 more... NOT Profiling to 'initial_balance.prof' wall-time delta: 28.04s NOT Profiling to 'deleting_200_rebalance.prof' wall-time delta: 9.35s NOT Profiling to 'first_rebalance.prof' wall-time delta: 16.41s The driver script I used is available here: https://gist.github.com/adb982aec6f0709f1273 Change-Id: I17e270acb12b5e4d4bbb1e34d8867dea90678961
This commit is contained in:
Darrell Bishop
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62e71a2b1f
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ec084de189
@ -641,65 +641,97 @@ class RingBuilder(object):
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sorted((d for d in self._iter_devs() if d['weight']),
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key=lambda x: x['sort_key'])
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tier2children = build_tier_tree(available_devs)
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tier2devs = defaultdict(list)
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tier2sort_key = defaultdict(list)
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tiers_by_depth = defaultdict(set)
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max_tier_depth = 0
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for dev in available_devs:
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for tier in tiers_for_dev(dev):
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tier2devs[tier].append(dev) # <-- starts out sorted!
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tier2sort_key[tier].append(dev['sort_key'])
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tiers_by_depth[len(tier)].add(tier)
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if len(tier) > max_tier_depth:
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max_tier_depth = len(tier)
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tier2children_sets = build_tier_tree(available_devs)
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tier2children = defaultdict(list)
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tier2children_sort_key = {}
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tiers_list = [()]
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depth = 1
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while depth <= max_tier_depth:
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new_tiers_list = []
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for tier in tiers_list:
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child_tiers = list(tier2children_sets[tier])
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child_tiers.sort(key=lambda t: tier2sort_key[t][-1])
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tier2children[tier] = child_tiers
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tier2children_sort_key[tier] = map(
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lambda t: tier2sort_key[t][-1], child_tiers)
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new_tiers_list.extend(child_tiers)
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tiers_list = new_tiers_list
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depth += 1
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for part, replace_replicas in reassign_parts:
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# Gather up what other tiers (zones, ip_ports, and devices) the
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# replicas not-to-be-moved are in for this part.
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other_replicas = defaultdict(lambda: 0)
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other_replicas = defaultdict(int)
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unique_tiers_by_tier_len = defaultdict(set)
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for replica in xrange(self.replicas):
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if replica not in replace_replicas:
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dev = self.devs[self._replica2part2dev[replica][part]]
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for tier in tiers_for_dev(dev):
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other_replicas[tier] += 1
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def find_home_for_replica(tier=(), depth=1):
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# Order the tiers by how many replicas of this
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# partition they already have. Then, of the ones
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# with the smallest number of replicas, pick the
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# tier with the hungriest drive and then continue
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# searching in that subtree.
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#
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# There are other strategies we could use here,
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# such as hungriest-tier (i.e. biggest
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# sum-of-parts-wanted) or picking one at random.
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# However, hungriest-drive is what was used here
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# before, and it worked pretty well in practice.
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#
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# Note that this allocator will balance things as
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# evenly as possible at each level of the device
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# layout. If your layout is extremely unbalanced,
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# this may produce poor results.
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candidate_tiers = tier2children[tier]
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min_count = min(other_replicas[t] for t in candidate_tiers)
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candidate_tiers = [t for t in candidate_tiers
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if other_replicas[t] == min_count]
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candidate_tiers.sort(
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key=lambda t: tier2sort_key[t][-1])
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if depth == max(tiers_by_depth.keys()):
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return tier2devs[candidate_tiers[-1]][-1]
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return find_home_for_replica(tier=candidate_tiers[-1],
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depth=depth + 1)
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unique_tiers_by_tier_len[len(tier)].add(tier)
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for replica in replace_replicas:
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dev = find_home_for_replica()
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tier = ()
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depth = 1
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while depth <= max_tier_depth:
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# Order the tiers by how many replicas of this
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# partition they already have. Then, of the ones
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# with the smallest number of replicas, pick the
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# tier with the hungriest drive and then continue
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# searching in that subtree.
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#
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# There are other strategies we could use here,
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# such as hungriest-tier (i.e. biggest
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# sum-of-parts-wanted) or picking one at random.
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# However, hungriest-drive is what was used here
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# before, and it worked pretty well in practice.
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#
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# Note that this allocator will balance things as
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# evenly as possible at each level of the device
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# layout. If your layout is extremely unbalanced,
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# this may produce poor results.
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#
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# This used to be a cute, recursive function, but it's been
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# unrolled for performance.
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candidate_tiers = tier2children[tier]
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candidates_with_replicas = \
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unique_tiers_by_tier_len[len(tier) + 1]
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if len(candidate_tiers) > len(candidates_with_replicas):
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# There exists at least one tier with 0 other replicas,
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# so work backward among the candidates, accepting the
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# first which isn't in other_replicas.
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#
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# This optimization is to avoid calling the min()
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# below, which is expensive if you've got thousands of
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# drives.
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for t in reversed(candidate_tiers):
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if other_replicas[t] == 0:
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tier = t
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break
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else:
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min_count = min(other_replicas[t]
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for t in candidate_tiers)
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tier = (t for t in reversed(candidate_tiers)
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if other_replicas[t] == min_count).next()
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depth += 1
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dev = tier2devs[tier][-1]
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dev['parts_wanted'] -= 1
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dev['parts'] += 1
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old_sort_key = dev['sort_key']
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new_sort_key = dev['sort_key'] = self._sort_key_for(dev)
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for tier in tiers_for_dev(dev):
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other_replicas[tier] += 1
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unique_tiers_by_tier_len[len(tier)].add(tier)
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index = bisect.bisect_left(tier2sort_key[tier],
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old_sort_key)
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@ -711,6 +743,22 @@ class RingBuilder(object):
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tier2devs[tier].insert(new_index, dev)
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tier2sort_key[tier].insert(new_index, new_sort_key)
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# Now jiggle tier2children values to keep them sorted
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new_last_sort_key = tier2sort_key[tier][-1]
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parent_tier = tier[0:-1]
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index = bisect.bisect_left(
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tier2children_sort_key[parent_tier],
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old_sort_key)
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popped = tier2children[parent_tier].pop(index)
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tier2children_sort_key[parent_tier].pop(index)
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new_index = bisect.bisect_left(
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tier2children_sort_key[parent_tier],
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new_last_sort_key)
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tier2children[parent_tier].insert(new_index, popped)
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tier2children_sort_key[parent_tier].insert(
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new_index, new_last_sort_key)
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self._replica2part2dev[replica][part] = dev['id']
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# Just to save memory and keep from accidental reuse.
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