高级数据库课件:-A-Dyanmo.pptx
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1、10/22/20121Distributed key/value storage systemScalableHighly availableCAP10/22/20122It sacrifices strong consistency for availability: always writableIncremental scalabilitySymmetry: every node should have the same set of responsibilities as its peersDecentralizationHeterogeneity10/22/20123Data par
2、titioningReplicationData versioningDynamo APIMembership managementApplication can deliver its functionality in abounded time: Every dependency in the platform needs to deliver its functionality with even tighter bounds.Example: service guaranteeing that it will provide a response within 300ms for 99
3、.9% of its requests for a peak client load of 500 requests per second.Service-oriented architecture of Amazons platformIf size of data exceeds the capacity of a single machine: partitioningSharding data (horizontal partitioning).Consistent hashing is one form of automatic sharding.hash(Fatemeh) = 12
4、hash(Ahmad) = 2hash(Seif) = 9hash(Jim) = 14hash(Sverker) = 4Hash both data and nodes using the same hash function in a same id space.partition = hash(d) mod n, d: data, n: number of nodesNODE IDENTIERS MAY NOT BE BALANCED.DATA IDENTIERS MAY NOT BE BALANCED.10/22/20129HOT SPOTS.HETEROGENEOUS NODES.10
5、/22/201210Each physical node picks multiple random identifiers.Each identifier represents a virtual node.Each node runs multiple virtual nodes.10/22/201211If a node becomes unavailable the load handled by this node is evenly dispersed across the remaining available nodes.10/22/201212When a node beco
6、mes available again, the newly available node accepts a roughly equivalent amount of load from each of the other available nodes.The number of virtual nodes that a node is responsible can decided based on its capacity, accounting for heterogeneity in the physical infrastructure.To achieve high avail
7、ability and durability, data should be replicates on multiple nodes.10/22/201213Updates are propagated asynchronously.Each update/modication of an item results in a new and immutable version of the data.Multiple versions of an object may exist.Replicas eventually become consistent.10/22/201214Versio
8、n branching can happen due to node/network failures.I Use vector clocks for capturing causality, in the form of (node, counter)If causal: older version can be forgottenIf concurrent: conflict exists, requiring reconciliationClient C1 writes new object via Sx.C1 updates the object via Sx.C1 updates t
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