rls: delegate pick to child policy as long as it is not in TransientFailure #5656
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easwars
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dfawley
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Sep 15, 2022
balancer/rls/picker.go
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| // to which this RPC can be routed to. If there is no child policy in READY | ||
| // state, we delegate to the first child policy arbitrarily. | ||
| // to which this RPC can be routed to. If all child policies are in | ||
| // TRANSIENT_FAILURE, we delegate to the first child policy arbitrarily. |
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Should we delegate to the last child policy to match C++? (Change itself should be ~trivial; e.g. check if loop iterator (currently _) is len(dcEntry.childPolicyWrappers)-1, in which case don't continue even if TRANSIENT_FAILURE.)
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I thought about it when making the change, but was lazy to make it and thought you wouldn't ask for it ... lol
dfawley
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Recently, we implemented a no-op
ExitIdlemethod for the ringhash LB policy in #5614.When RLS is used in conjunction with ringhash though, this causes the channel to never come out of
IDLE, as ringhash starts inIDLEand any requests to exit idle from its parent results in a no-op.The pick behavior in RLS though seems to be the root cause. Instead of delegating the picks to child policies which are not in
TransientFailure, RLS was asking them to exit idle if they were inIDLE. This is in contrast to how things are implemented in c-core, which simply delegates the picks to the child policies as long as they are not inTransientFailure, and for a policy likeringhash, the pick ensures that it exits idle.RELEASE NOTES:
IDLE