A80: gRPC Metrics for TCP connection #428
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markdroth
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nanahpang
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nanahpang
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dfawley
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atollena
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| | Name | Type | Unit | Labels | Description | | ||
| | ------------- | ----- | ----- | ------- | ----------- | | ||
| | grpc.tcp.min_rtt | Histogram (double) | s | None | Records TCP's current estimate of minimum round trip time (RTT), typically used as an indication of the network health between two endpoints.<br /> RTT = packet acked timestamp - packet sent timestamp. | |
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Buckets for histogram are explicitly specified for request latency in https://github.com/grpc/proposal/blob/master/A66-otel-stats.md. Do you plan to reuse the same buckets? It might be worth specifying.
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Thanks for the suggestion, but using buckets for the min_rtt metric wouldn't offer much significant insights. The value of min_rtt is bound to the physical length of the path between sender and receiver or the queueing time caused by throttling and load. A step-change in min_rtt values usually means that traffic is being throttled or experiencing congestion, or has been re-routed through a different path. I think it's better to opt out buckets in this situation.
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@nanahpang If you do not specify buckets, we will get the default OpenTelemetry buckets which is { 0, 5, 10, 25, 50, 75,100, 250, 500, 750, 1000, 2500, 5000, 7500, 10000}. Are there better defaults that we can suggest or do we leave it to the user to figure it out?
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Regarding OpenTelemetry buckets, if you're referring to a plugin used for exporting metrics, that would be a separate concern from the metric types we're defining here. However, I agree that specifying a smaller range for the min_rtt metric buckets is the right approach, especially since we're using seconds as the unit (to align with the open-source standard) while the underlying measurements are usually in microseconds.
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| | Name | Type | Unit | Labels | Description | | ||
| | ------------- | ----- | ----- | ------- | ----------- | | ||
| | grpc.tcp.min_rtt | Histogram (double) | s | None | Records TCP's current estimate of minimum round trip time (RTT), typically used as an indication of the network health between two endpoints.<br /> RTT = packet acked timestamp - packet sent timestamp. | |
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@nanahpang If you do not specify buckets, we will get the default OpenTelemetry buckets which is { 0, 5, 10, 25, 50, 75,100, 250, 500, 750, 1000, 2500, 5000, 7500, 10000}. Are there better defaults that we can suggest or do we leave it to the user to figure it out?
Update proposal with more information
Add the proposal of gRPC TCP per-connection metrics.