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Posted to commits@cassandra.apache.org by "Kenneth Brotman (JIRA)" <ji...@apache.org> on 2018/03/01 13:08:00 UTC
[jira] [Commented] (CASSANDRA-14265) Add explanation of vNodes to
online documentation
[ https://issues.apache.org/jira/browse/CASSANDRA-14265?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16381968#comment-16381968 ]
Kenneth Brotman commented on CASSANDRA-14265:
---------------------------------------------
From the Dynamo paper:
The basic consistent hashing algorithm presents some challenges. First, the random position assignment of each node on the ring leads to non-uniform data and load distribution. Second, the basic algorithm is oblivious to the heterogeneity in the performance of nodes. To address these issues, Dynamo uses a variant of consistent hashing (similar to the one used in [10, 20]): instead of mapping a node to a single point in the circle, each node gets assigned to multiple points in the ring. To this end, Dynamo uses the concept of “virtual nodes”. A virtual node looks like a single node in the system, but each node can be responsible for more than one virtual node. Effectively, when a new node is added to the system, it is assigned multiple positions (henceforth, “tokens”) in the ring. The process of fine-tuning Dynamo’s partitioning scheme is discussed in Section 6. Using virtual nodes has the following advantages: • If a node becomes unavailable (due to failures or routine maintenance), the load handled by this node is evenly dispersed across the remaining available nodes. • When a node becomes available again, or a new node is added to the system, 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
> Add explanation of vNodes to online documentation
> -------------------------------------------------
>
> Key: CASSANDRA-14265
> URL: https://issues.apache.org/jira/browse/CASSANDRA-14265
> Project: Cassandra
> Issue Type: Improvement
> Components: Documentation and Website
> Reporter: Kenneth Brotman
> Priority: Major
>
> A lot of inquiries on the mailing list about how vNodes work and how to set configuration properly. We should add an explanation to the documentation.
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