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From "Paulo Motta (Jira)" <j...@apache.org>
Subject [jira] [Updated] (CASSANDRA-16138) Refactor Local Ring Management
Date Wed, 23 Sep 2020 14:35:00 GMT

     [ https://issues.apache.org/jira/browse/CASSANDRA-16138?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Paulo Motta updated CASSANDRA-16138:
------------------------------------
    Attachment: vnode-lifecyle.png

> Refactor Local Ring Management
> ------------------------------
>
>                 Key: CASSANDRA-16138
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-16138
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Cluster/Membership, Feature/Virtual Nodes, Legacy/Distributed Metadata
>            Reporter: Paulo Motta
>            Assignee: Paulo Motta
>            Priority: Normal
>         Attachments: vnode-lifecyle.png
>
>
> Token ring management is one of the most critical parts of Cassandra, yet one of the
most overlooked. Some of the problems include but are not limited to:
> * Complexity (ie. [pending range calculation|https://github.com/apache/cassandra/blob/8ba163f25a56cb507e621b89b6928c2aef0ecc57/src/java/org/apache/cassandra/locator/TokenMetadata.java#L878])

> * Inefficiency (ie. [pending range calculation|https://github.com/apache/cassandra/blob/8ba163f25a56cb507e621b89b6928c2aef0ecc57/src/java/org/apache/cassandra/locator/TokenMetadata.java#L878],
[AbstractReplicationStrategy.getAddressReplicas|https://github.com/apache/cassandra/blob/33eada06a6dd3529da644377dba180795f522176/src/java/org/apache/cassandra/locator/AbstractReplicationStrategy.java#L233])
> * Prone to race conditions (ie. [here|https://github.com/apache/cassandra/blob/8ba163f25a56cb507e621b89b6928c2aef0ecc57/src/java/org/apache/cassandra/locator/ReplicaLayout.java#L198])
> * Poor modularity and consistency (ie. natural replicas computed from [NetworkTopologyStrategy|https://github.com/apache/cassandra/blob/8ba163f25a56cb507e621b89b6928c2aef0ecc57/src/java/org/apache/cassandra/locator/NetworkTopologyStrategy.java]
and pending replicas computed from [TokenMetadata|https://github.com/apache/cassandra/blob/8ba163f25a56cb507e621b89b6928c2aef0ecc57/src/java/org/apache/cassandra/locator/TokenMetadata.java#L1271])
> * Insufficient testing (due to complexity and poor modularity)
> These limitations make it difficult to reliably fix bugs like properly supporting node
replacement with the same IP address (CASSANDRA-12344), add improvements such as safe ring
membership changes, support for networking via identity instead of IP (CASSANDRA-15823) or
add new features such as dynamic virtual nodes.
> This ticket aims at refactoring the ring management sub-module (namely TokenMetadata
and related classes) to address most of its current limitations in order to support further
improvements and new features.
> Some of the requirements of the proposed refactoring are:
> # Make node-local ring representation fully immutable and snapshottable.
> # Add content-based versioning to uniquely identify a ring snapshot throughout the cluster.
> # Make token ring management vnode-centric to support membership operations on individual
tokens and simplify token assignment calculations.
> # Primarily identify ring endpoints by node ID to decouple a node’s identity from its
IP address.
> # Add a local publish/subscribe mechanism for ring change notifications, so other modules
can subscribe to it and receive the newest snapshot of the ring after membership changes.
> # Add testing framework to verify correctness of ring membership operations.
> # Ensure the refactored sub-module does not change current behavior via comprehensive
testing.



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