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49 lines
1.6 KiB
Markdown
49 lines
1.6 KiB
Markdown
# ORCA Load Reporting
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ORCA is a protocol for reporting load between servers and clients. This
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example shows how to implement this from both the client and server side. For
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more details, please see [gRFC
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A51](https://github.com/grpc/proposal/blob/master/A51-custom-backend-metrics.md)
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## Try it
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```
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go run server/main.go
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```
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```
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go run client/main.go
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```
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## Explanation
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gRPC ORCA support provides two different ways to report load data to clients
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from servers: out-of-band and per-RPC. Out-of-band metrics are reported
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regularly at some interval on a stream, while per-RPC metrics are reported
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along with the trailers at the end of a call. Both of these mechanisms are
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optional and work independently.
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The full ORCA API documentation is available here:
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https://pkg.go.dev/google.golang.org/grpc/orca
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### Out-of-band Metrics
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The server registers an ORCA service that is used for out-of-band metrics. It
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does this by using `orca.Register()` and then setting metrics on the returned
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`orca.Service` using its methods.
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The client receives out-of-band metrics via the LB policy. It receives
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callbacks to a listener by registering the listener on a `SubConn` via
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`orca.RegisterOOBListener`.
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### Per-RPC Metrics
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The server is set up to report query cost metrics in its RPC handler. For
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per-RPC metrics to be reported, the gRPC server must be created with the
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`orca.CallMetricsServerOption()` option, and metrics are set by calling methods
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on the returned `orca.CallMetricRecorder` from
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`orca.CallMetricRecorderFromContext()`.
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The client performs one RPC per second. Per-RPC metrics are available for each
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call via the `Done()` callback returned from the LB policy's picker.
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