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scylladb / scylla-rust-driver

Async CQL driver for Rust, optimized for ScyllaDB!
Apache License 2.0
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load balancing: slow coordinator avoidance #260

Open kbr- opened 3 years ago

kbr- commented 3 years ago

It would be nice to have a real load balancing strategy which chooses coordinators based on actual metrics such as how fast it can process requests.

See https://github.com/scylladb/scylla/issues/5715 for motivation. I explain in the comments what the issue is (it is a driver-side issue).

The 4.x versions of the Java driver AFAIK do have such strategies - at least one. From https://docs.datastax.com/en/developer/java-driver/4.11/manual/core/load_balancing/#built-in-policies:

DefaultLoadBalancingPolicy should almost always be used; it requires a local datacenter to be specified either programmatically when creating the session, or via the configuration (see below). It can also use a highly efficient slow replica avoidance mechanism, which is by default enabled.

piodul commented 1 year ago

Just leaving a note: support for latency-aware load balancing policy has been merged, however the new Java driver's DefaultLoadBalancingPolicy uses a different algorithm. I hope that the Java driver's algorithm performs better - Java driver deprecated the latency aware policy and later introduced the default one - so we should implement something similar and compare how well it performs relative to latency aware policy.