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Global Analytics in the Face of Bandwidth and Regulatory Constraints

Takeaways from Global Analytics in the Face of Bandwidth and Regulatory Constraints, Vulimiri et al, NSDI, 2015.

Existing Approach

  • Existing Approach for Global Analytics: Transfer data to a central data center.
  • Issues:
    • Transfers significant data volumes.
    • Limit on the number of applications due to limited cross-border network bandwidth.
    • Network capacity growth is decelerating.
    • Regulatory constraints on data movement.

Problem Geode tries to solve:

Provide wide area analytics while minimizing bandwidth over geo-distributed data structured as SQL tables.

Assumption

Resources within a single data center are relatively cheap compared to cross-data center bandwidth.

Architecture.

  • Central Command Layer.
  • Thin proxy layer atop local analytics stack.
  • Central Workload Optimizer.

Details.

  • Subquery Deltas.
    • Cache query results at the source and destination with the query’s signature.
    • Instead of sending fresh results, send only a diff (delta) between the new and old results.
    • Cache results on a sub-query basis.
  • Workload Optimizer.
    • Identify optimal centralized plan.
    • Use default Calcite implementation.
    • Rough SQL table statistics in Hive to get an optimized join algorithm selection.
    • Use pseudo-distributed measurement to estimate data movement.
    • Simulate a virtual topology in which each base data partition is a separate datacenter, even if the data is centralized.
    • Achieved by rewriting SQL queries to simulate data partitions.
    • Evaluate alternative data partitions to get an indication of optimal. To reduce the sample space, do a worst case evaluation (worst data partition).
    • Combine all measurements to jointly solve site selection and data replication problem.
    • Formulate an ILP to jointly solve both problems to minimize total bandwidth cost.
    • Due to scalability constraints, alternatively use greedy approach.
    • Solve site selection problem in isolation based on sovereignity constraints.
    • Greedily pick the datacenter to copy input data needed per-task based on lowest cost.