> Which "request"? What is this "request"? What does it contain? Why is it 76026807?
A request in this context is a basic call from a HDFS client. A few example requests from a client could be "list this directory", "create a file", etc.
The request type is not determined at the point where the error is thrown because the 64 MB length limit safety check fires before we can deserialize/interpret the request.
As to what it contains, its not clear from the error. What is odd definitely is its size. Most client requests carry very simple attributes in them, such as a path, a list of locations, a flag and so on. Nothing in a regular client's request should be this large, unless perhaps the client in question is using ginormously large paths.
In the other cases I've seen this message, the port of request is usually 8022 which is where DataNodes send their heartbeats and block reports. These sort of 'requests' can be large depending on the amount of blocks or other datasets being sent.
Assuming you are running a configuration that uses 8020 + 8022 both, it is quite odd to observe this error over 8020. It could be a rogue client such as a network scanner sending bogus or specially crafted data for vulnerability checks (in which case this is normal to see, and is acting as designed in rejecting such requests).
You can find out more by trying to spot the program running on the client IP shown in the error, and see what form of API calls its trying to make (or if it even is a valid client).
