Prefer FixedResultPicker over custom Picker implementations #12590
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These other implementations pre-date FixedResultPicker, and are no longer needed.
gRPC-LB's tests failed when using FixedResultPicker because it didn't transition to READY. This was because GrpclbState.maybeUpdatePicker() didn't consider the ConnectivityState when checking if anything had changed. The old PickFirstLoadBalancer.Picker didn't implement equals() so every update was considered different, ignoring the connectivity state. PickFirstLeafLoadBalancer wasn't impacted because it didn't pick a subchannel when in CONNECTING, and neither did PickFirstLoadBalancer after the first update. This is fixed on both sides: PickFirstLoadBalancer no londer returns the useless subchannel when picking during CONNECTING, and gRPC-LB now checks the connectivity state. This now causes what appears to be a bug in RLS. That is still being investigated.
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lb_serverStatusCodeConversion() has been misleading since 42e1829 ("xds: Do RLS fallback policy eagar start"). At that point, the subchannel it marked as READY was for the default target's policy, not the policy for wilderness. However, since old PF policy provided a subchannel when CONNECTING, everything was "fine", but RLS would mistakenly count toward target_picks. This demonstrates that target_picks has been broken since it was introduced for PF, as PF relied on the caller to avoid the picker when it was CONNECTING. This may have been hard to notice in production, as the metrics become correct as soon as the connection is established, so as long as you use the channel for a while, the duplicate counting would become a small percentage of the overall amount.
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@kannanjgithub, FYI, the second commit here ("Fix grpclb incompatibility") ends up fixing an RLS metric bug. See the "Fix RLS test" for a description of the bug. |
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These other implementations pre-date FixedResultPicker, and are no longer needed.