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  1. Cassandra
  2. CASSANDRA-15600

Algorithmic token allocation does not handle the racks = RF case well

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    Details

    • Bug Category:
      Correctness
    • Severity:
      Normal
    • Complexity:
      Normal
    • Discovered By:
      User Report
    • Platform:
      All
    • Impacts:
      Docs
    • Since Version:
    • Test and Documentation Plan:
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      In the cases where the keyspace replication factor is ONE, or if the keyspace replication factor is equal to the number of racks in the datacenter, the workload variance drops from ~10 percent to ~6 percent due to algorithmic optimizations.

       

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      In the cases where the keyspace replication factor is ONE, or if the keyspace replication factor is equal to the number of racks in the datacenter, the workload variance drops from ~10 percent to ~6 percent due to algorithmic optimizations.  

      Description

      When the number of racks in a data centre is equal to the replication factor, the node allocation algorithm may calculate the target ownership incorrectly and allocate unsuitable tokens. This causes some inefficiency when the number of nodes in the DC is small, and significant problems if the number of nodes in each rack is different.

      In this case (racks count equal to replication factor) the load within each rack is effectively distributed independently. The allocation algorithm should reflect that, restricting the allocation space to the rack (instead of the DC) and using the RF=1 solution.

        Attachments

        1. Screen Shot 2020-03-02 at 6.55.41 PM.png
          781 kB
          Ekaterina Dimitrova
        2. CASSANDRA-15600 unit.txt
          277 kB
          Ekaterina Dimitrova
        3. CASSANDRA-15600-jvm.txt.zip
          10.33 MB
          Ekaterina Dimitrova

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            • Assignee:
              e.dimitrova Ekaterina Dimitrova
              Reporter:
              blambov Branimir Lambov
              Authors:
              Ekaterina Dimitrova
              Reviewers:
              Brandon Williams
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              Dates

              • Created:
                Updated:
                Resolved: