MaxMessageSize is not altered, making delivery impossible over gRPC for some APIs

[mdietz94]

For Cloud Pub/Sub, the maximum possible PullResponse is 20 MB large. The default gRPC Channel maxMessageSize is 4 MB. This should be configured per API, or some messages will be silently undeliverable.

[garrettjonesgoogle]

@ejona86 , is there a drawback to setting maxMessageSize to a large value for all APIs?

[ejona86]

The user would have to be willing to receive large responses, and remember that they can explode in size when deserializing. The max message size is there to prevent large requests/responses without actually considering the stability impact to the service/users.

If a user uploads a 20 MB message, then it can be reasonable to increase the default limit and let them receive it. If the user uploads 20 x 1 MB messages, and they are all sent back all-at-once in one response, then it seems like it could be surprising to the user and may contribute to OOM. Let's just say someone was using the service from a mobile phone. I'm not saying that's a good idea, but 20 MB is a lot of memory to some users still (and it could easily be 100 MB or more after deserializing).

The 4 MB is arbitrary, so you can change it to another arbitrary value. gRPC itself is okay with a message being 100s of MBs and we know services that adjust the limit to do so. But the limit is there for a reason.

[garrettjonesgoogle]

This is blocked on grpc/grpc-java#2563 .

[garrettjonesgoogle]

Let's use ManagedChannelBuilder.maxInboundMessageSize(int) from GAX.