This is the v1 of the patch for Solrcloud Rebalance api (as described in http://engineering.bloomreach.com/solrcloud-rebalance-api/) , built at Bloomreach by Nitin Sharma and Suruchi Shah. The goal of the API is to provide a zero downtime mechanism to perform data manipulation and efficient core allocation in solrcloud. This API was envisioned to be the base layer that enables Solrcloud to be an auto scaling platform. (and work in unison with other complementing monitoring and scaling features).
The patch is work in progress and incremental. We have done a few rounds of code clean up. We wanted to get the patch going first to get initial feed back. We will continue to work on making it more open source friendly and easily testable.
The platform is deployed in production at bloomreach and has been battle tested for large scale load. (millions of documents and hundreds of collections).
The internals of the API and performance : http://engineering.bloomreach.com/solrcloud-rebalance-api/
It is built on top of the admin collections API as an action (with various flavors). At a high level, the rebalance api provides 2 constructs:
Scaling Strategy: Decides how to move the data. Every flavor has multiple options which can be reviewed in the api spec.
Re-distribute - Move around data in the cluster based on capacity/allocation.
Auto Shard - Dynamically shard a collection to any size.
Smart Merge - Distributed Mode - Helps merging data from a larger shard setup into smaller one. (the source should be divisible by destination)
Scale up - Add replicas on the fly
Scale Down - Remove replicas on the fly
Allocation Strategy: Decides where to put the data. (Nodes with least cores, Nodes that do not have this collection etc). Custom implementations can be built on top as well. One other example is Availability Zone aware. Distribute data such that every replica is placed on different availability zone to support HA.
Detailed API Spec:
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