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106 lines
3.0 KiB
Nim
106 lines
3.0 KiB
Nim
## Waku autosharding utils
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##
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## See 51/WAKU2-RELAY-SHARDING RFC: https://rfc.vac.dev/spec/51/#automatic-sharding
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when (NimMajor, NimMinor) < (1, 4):
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{.push raises: [Defect].}
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else:
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{.push raises: [].}
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import
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nimcrypto,
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std/options,
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std/math,
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std/sequtils,
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std/algorithm,
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stew/endians2,
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stew/results,
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stew/byteutils
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import
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./content_topic,
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./pubsub_topic
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## For indices allocation and other magic numbers refer to RFC 51
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const ClusterIndex* = 49152
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const GenerationZeroShardsCount* = 5
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type ShardsPriority = seq[tuple[topic: NsPubsubTopic, value: float64]]
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proc shardCount*(topic: NsContentTopic): Result[int, string] =
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## Returns the total shard count, sharding selection bias
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## and the shard name from the content topic.
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let shardCount =
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if topic.generation.isNone():
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## Implicit generation # is 0 for all content topic
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GenerationZeroShardsCount
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else:
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case topic.generation.get():
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of 0:
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GenerationZeroShardsCount
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else:
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return err("Generation > 0 are not supported yet")
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ok((shardCount))
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proc biasedWeights*(shardCount: int, bias: ShardingBias): seq[float64] =
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var weights = repeat(1.0, shardCount)
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case bias:
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of Unbiased:
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return weights
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of Lower20:
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# we choose the lower 20% of shards and double their weigths
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let index = shardCount div 5
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for i in (0..<index):
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weights[i] *= 2.0
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of Higher80:
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# we choose the higher 80% of shards and double their weigths
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let index = shardCount div 5
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for i in (index..<shardCount):
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weights[i] *= 2.0
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weights
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proc applyWeight(hashValue: uint64, weight: float64): float64 =
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(-weight) / math.ln(float64(hashValue) / float64(high(uint64)))
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proc hashOrder*(x, y: (NsPubsubTopic, float64)): int =
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cmp(x[1], y[1])
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proc weightedShardList*(topic: NsContentTopic, shardCount: int, weightList: seq[float64]): Result[ShardsPriority, string] =
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## Returns the ordered list of shards and their priority values.
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if weightList.len < shardCount:
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return err("Must provide weights for every shards")
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let shardsNWeights = zip(toSeq(0..shardCount), weightList)
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var list = newSeq[(NsPubsubTopic, float64)](shardCount)
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for (shard, weight) in shardsNWeights:
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let pubsub = NsPubsubTopic.staticSharding(ClusterIndex, uint16(shard))
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let clusterBytes = toBytesBE(uint16(ClusterIndex))
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let shardBytes = toBytesBE(uint16(shard))
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let bytes = toBytes(topic.application) & toBytes(topic.version) & @clusterBytes & @shardBytes
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let hash = sha256.digest(bytes)
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let hashValue = uint64.fromBytesBE(hash.data)
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let value = applyWeight(hashValue, weight)
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list[shard] = (pubsub, value)
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list.sort(hashOrder)
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ok(list)
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proc singleHighestWeigthShard*(topic: NsContentTopic): Result[NsPubsubTopic, string] =
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let count = ? shardCount(topic)
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let weights = biasedWeights(count, topic.bias)
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let list = ? weightedShardList(topic, count, weights)
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let (pubsub, _) = list[list.len - 1]
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ok(pubsub)
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