pubsub/gcppubsub: decrease max batch buffer size from 9MB to 8MB (#3698)

Author: vangent

pubsub/gcppubsub/gcppubsub.go

@@ -86,9 +86,9 @@ var sendBatcherOpts = &batcher.Options{
 	MaxHandlers:  2,
 	// The PubSub service limits the size of the request body in a single Publish RPC.
 	// The limit is currently documented as "10MB (total size)" and "10MB (data field)" per message.
-	// We are enforcing 9MiB to give ourselves some headroom for message attributes since those
+	// We are enforcing 8MiB to give ourselves some headroom for message attributes since those
 	// are currently not considered when computing the byte size of a message.
-	MaxBatchByteSize: 9 * 1024 * 1024,
+	MaxBatchByteSize: 8 * 1024 * 1024,
 }
 
 var defaultRecvBatcherOpts = &batcher.Options{