6 - Network Transport Layer on Apache Dubbo

6-1 - Server Connection Failure

Mon, 01 Jan 0001 00:00:00 +0000

Network communication layer, failure to connect to the service provider’s service.

Possible Causes

The service provider’s network is unexpectedly disconnected or intercepted by firewalls and third-party tools, unable to provide external services.

Troubleshooting and Solution Steps

If it’s a REST connection, check if the server configuration for the request is correct.
Check if the network communication is normal; you can use some simple CMD commands for detection, such as ping, etc.

6-2 - Client Timeout

Mon, 01 Jan 0001 00:00:00 +0000

Timeout occurs when the caller is unable to receive a corresponding response within a specified time after sending the request.

Possible Causes

The server is indeed processing slowly and cannot return results within the specified time, causing the caller to automatically return a timeout exception response to terminate the call.
If the server responds quickly, but when the client is under heavy load, issues like requests being unable to be sent or responses getting stuck in the TCP Buffer can cause timeouts. This is because data sent from the server or requests from the client get queued at the system level, and if system load is high, the kernel time will increase, resulting in a timeout by the time the client receives the value.
Usually, this is due to slow business processing. You can execute jstack [PID] > jstack.log on the service provider’s machine to analyze where the threads are stuck, identifying the cause of slowness. If performance cannot be optimized, consider increasing the timeout threshold.

Troubleshooting and Resolution Steps

Both sides may have GC occurring. Check the GC logs on both the server and client. Prolonged GC can lead to timeouts. The occurrence of a timeout likely indicates resource bottlenecks (CPU, memory, or network) on either the caller or server; thus, it’s necessary to check for GC jitter, among other issues.
Check the network quality of the server, such as retransmission rates to rule out network issues.
Utilize link tracing analysis services (like Alibaba’s ARMS, open-source implementations of OpenTracing, Zipkin, SkyWalking, etc.) to analyze the timing of each point.

This error code’s FAQ page references Kong Ming’s article “Common Errors and Solutions in Dubbo”.
The cited article permits compilation under the CC-BY-4.0 license. Special thanks to the original author.

6-3 - Network connection closure failure

Mon, 01 Jan 0001 00:00:00 +0000

Possible Causes

Non-graceful shutdown of the service, during which the server may not have completed its output stream.

Troubleshooting and Resolution Steps

Generally, this is a notification-type warning that does not affect subsequent program execution.

6-4 - Unknown Exception in Network Communication Layer

Mon, 01 Jan 0001 00:00:00 +0000

Possible Causes

The meaning of this error code has been adjusted. For the error of this error code in Dubbo 3.1.4, 3.2.0-beta.3, and earlier versions, please refer to error code 99-0.

Troubleshooting and Resolution Steps

(This error code currently has no details)

6-5 - Network disconnection failure

Mon, 01 Jan 0001 00:00:00 +0000

Possible Causes

Timeout occurs when the caller is unable to receive the corresponding response within the specified time after the request is sent, leading to the client actively disconnecting.

Troubleshooting and Resolution Steps

It is generally a warning message that does not affect the subsequent execution of the program.

6-6 - Unsupported Message

Mon, 01 Jan 0001 00:00:00 +0000

Possible Reasons

Data serialization errors or exceeding the maximum serialization value.

Troubleshooting and Resolution Steps

You can analyze the stack information using some third-party tools or by running jstack [PID] > jstack.log for diagnosis.

For specific configuration items supported by each component and their meanings, please refer to the Configuration Manual

6-7 - Thread connection count exceeds warning

Mon, 01 Jan 0001 00:00:00 +0000

Possible Causes

Warning message when the number of connections exceeds the limit, alerting that the configured connection count has been exceeded.

Troubleshooting and Resolution Steps

The default configuration item connect.queue.warning.size=1000 can be adjusted through configuration.

6-8 - Failed to decode return data

Mon, 01 Jan 0001 00:00:00 +0000

Possible Causes

Incorrect return data format or decoding failure

Troubleshooting and Resolution Steps

You can output the specific service class name along with the returned message and stack information by using the debug/warn log mode.

6-9 - Duplicate Serial Number ID

Mon, 01 Jan 0001 00:00:00 +0000

Possible Causes

An empty object was returned.
A custom serial number class, org.apache.dubbo.common.serialize.Serialization#getContentTypeId, duplicates with the system built-in. In this case, the first loaded SPI instance will prevail. Other entries will be skipped.

Troubleshooting and Resolution Steps

Check the return result.
Built-in values can refer to the class org.apache.dubbo.common.serialize.Constants

6-10 - Payload Limit Exceeded Exception

Mon, 01 Jan 0001 00:00:00 +0000

Possible Causes

Default payload=8M, please check the configurations.

Troubleshooting and Resolution Steps

For specific configuration items supported by each component and their meanings, please refer to the Configuration Manual.

6-11 - Character set not supported

Mon, 01 Jan 0001 00:00:00 +0000

Possible Reasons

Default UTF-8 character set

Troubleshooting and Resolution Steps

The result will ultimately be processed with the UTF-8 character set.

6-12 - Error occurring during ZK client destruction

Mon, 01 Jan 0001 00:00:00 +0000

Possible Causes

The connection between the client and server has been refused. When the client is being destroyed, the server may be undergoing an election or other operations, resulting in an exception.

Troubleshooting and Resolution Steps

The shutdown method can be queried based on stack information. Generally, no further action is required.

6-13 - Stream Closed Exception

Mon, 01 Jan 0001 00:00:00 +0000

Possible Causes

The current stream is closed Stream is closed or another thread is reading while the stream is closing.

Troubleshooting and Resolution Steps

Typically, this occurs due to the incorrect order in which the code closes the stream.

6-14 - Server response failure

Mon, 01 Jan 0001 00:00:00 +0000

Possible Causes

The client unexpectedly closes the connection when exchanging data with the server.

Troubleshooting and Resolution Steps

The client terminates unexpectedly or the server crashes.

6-15 - Skip unread stream data

Mon, 01 Jan 0001 00:00:00 +0000

Possible Reasons

When decoding, unread data in the stream will be skipped if there is still unread data present.

Troubleshooting and Resolution Steps

Data will be read all at once during decoding.

6-16 - Exception Occurred During Reconnection

Mon, 01 Jan 0001 00:00:00 +0000

Possible Causes

An unstable network causes delayed reconnections each time a reconnection occurs.

Troubleshooting and Resolution Steps

Check for any network packet loss.