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Add rack-aware load balancing policy #73

Merged
merged 5 commits into from
Jan 18, 2023
Merged

Add rack-aware load balancing policy #73

merged 5 commits into from
Jan 18, 2023

Commits on Jan 2, 2023

  1. Display the query plans in case of failed test 

    The out was not helpful for understanding the failure of
a test.
Printing the query plans will help.
    @martin-sucha
    martin-sucha committed Jan 2, 2023
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  2. Use count argument in run_policy 

    This argument was not used anywhere, it worked by chance
since it had the same value everywhere.
    @martin-sucha
    martin-sucha committed Jan 2, 2023
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  3. Explicitly specify consistency level in run_policy 

    The Datstax C++ driver has default ONE,
the Scylla fork has LOCAL_ONE.
    @martin-sucha
    martin-sucha committed Jan 2, 2023
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  4. Add doc comments to helper functions

    @martin-sucha
    martin-sucha committed Jan 2, 2023
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  5. Add rack-aware load balancing policy 

    We need to prefer local rack as there are higher network costs
when communicating with nodes in remote rack.

This policy prefers nodes from the local rack, then local datacenter
and then other nodes.

The new RackAwarePolicy is similar to DCAwarePolicy,
but does not have the deprecated options.
TokenAwarePolicy and other code needed to be modified
so that the local rack is propagated.

The TokenAware policy was changed to prefer replicas in remote
rack / remote DC before trying non-replica nodes.
It does not make much sense to not try the replicas and
trying the replicas simplifies the code as now we have three
levels local/remote/remote2.

This change might not be backwards-compatible,
we don't know what exactly this project guarantees in terms of
backwards compatibility.

Co-Authored-By: Peter Navrátil <[email protected]>
    @martin-sucha
    martin-sucha and Peter Navrátil committed Jan 2, 2023
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