mirror of https://github.com/grpc/grpc-java.git
132f7a9a33
Highlights ========== StatsTraceContext ----------------- The bridge between gRPC library and Census. It keeps track of the total payload sizes and the elapsed time of a Call. The rest of the gRPC code doesn't invoke Census directly. Context propagation ------------------- StatsTraceContext carries CensusContext (and the upcoming TraceContext) and is attached to the gRPC Context. 1. StatsTraceContext is created by ManagedChannelImpl, by calling createClientContext(), which inherits the current CensusContext if available. 2. ManagedChannelImpl passes StatsTraceContext to ClientCallImpl, then to the stream, then to the framer and deframer explicitly. 3. ClientCallImpl propagates the CensusContext to the headers. 1. ServerImpl creates a StatsTraceContext by implementing a new callback method StatsTraceContext methodDetermined(MethodDescriptor, Metadata) on ServerTransportListener. 2. NettyServerHandler calls methodDetermined() before creating the stream, and passes the StatsTraceContext to the stream. 3. When ServerImpl creates the gRPC Context for the new ServerCall, it calls the new method statsTraceContext() on ServerStream and puts the StatsTraceContext in the Context. Metrics recording ----------------- 1. Client-side start time: when ClientCallImpl is created 2. Server-side start time: when methodDetermined() is called 3. Server-side end time: in ServerStreamListener.closed(), but before calling onComplete() or onCancel() on ServerCall.Listener. 4. Client-side end time: in ClientStreamListener.closed(), but before calling onClonse() on ClientCall.Listener Message sizes are recorded in MessageFramer and MessageDeframer. Both the uncompressed and wire (possibly compressed) payload sizes are counted. TODOs ===== The CensusContext created from headers on the server side should be attached to the gRPC Context for the call. It's not done at this moment because Census lacks the proper API to do it. It only affects tracing and resource accounting, but doesn't affect stats functionality |
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