C++ grpc::ClientBidiReactor high read latency

[Marc Tibout]

I am seeing high latency for the OnReadDone() callbacks in my C++ gRPC client for a bi-directional stream RPC.

Requests from the client and responses from the server are completely asynchronous.

Using grpc-dump (https://github.com/bradleyjkemp/grpc-tools) generated output, I see that incoming server responses are only triggering the OnReadDone() callback after a variable delay of 2 to 5 seconds.

There is no such issue with the requests sent to the server.

The OnReadDone(ok) implementation is systematically calling StartRead() once the incoming message has been processed (unless ok is false in which case the rpc is terminated).

Any idea what can be done to investigate further this issue?

Thanks!

OS: Linux

gRPC version: 1.34.1 (and 1.37.1)

[Marc Tibout]

I fixed the latency issue by setting the GRPC_CLIENT_CHANNEL_BACKUP_POLL_INTERVAL_MS environment variable to a small value (default is 5000 ms).