Single Thread for KEX Handling Causes Increased SSH Latency with High Concurrent Connections

[raajeive]

Version

2.12.1

Bug description

The issue is related to Apache MINA SSHD #458.

In version 2.12.1, a singleton thread pool was introduced for the Key Exchange (KEX) message handler flushing. This change has led to a significant increase in the time taken to establish SSH connections when a single client frequently connects to multiple servers. With only one thread available for KEX, this architecture becomes a bottleneck.

Our application frequently SSHs to over 10,000 servers to periodically poll specific information. Due to the single-threaded KEX, all 10,000 SSH connections now rely on the same thread, causing the average time to SSH into a server to increase. This directly impacts the application's polling frequency, leading to performance degradation.

Actual behavior

A single thread is used for KEX, leading to increased SSH time when the client handles several thousand SSH connections concurrently.

Expected behavior

Provide a configurable option to set the number of threads for KEX.

Relevant log output

No response

Other information

No response

[tomaswolf]

I don't understand. This is not a single thread; it's a thread pool. It sizes dynamically between zero and Integer.MAX_VALUE threads; idle threads are kept for one minute. So why are you seeing one thread only?