JMeter java.net.SocketTimeoutException

java.net.SocketTimeoutException in JMeter

Symptom

In the View Results Tree listener, jmeter.log, or JTL output, a sampler fails with:

Response code: Non HTTP response code: java.net.SocketTimeoutException
Response message: Non HTTP response message: Read timed out

Or during the initial TCP connection phase:

Response code: Non HTTP response code: java.net.SocketTimeoutException
Response message: Non HTTP response message: connect timed out

The sample is marked as failed without a standard HTTP status code (such as 200, 500, or 504).

Quick diagnosis (TL;DR)

SocketTimeoutException: Read timed out means JMeter connected successfully to the server, sent the request, but the server failed to transmit response bytes within the configured Response Timeout. connect timed out means the initial TCP 3-way handshake did not finish within the Connect Timeout.

Common causes

Cause	Specific Error	Why it happens
Slow server processing	Read timed out	Database locks, CPU saturation, or heavy downstream microservice calls delay response generation beyond client timeout
Full GC pause on server	Read timed out	Stop-the-world garbage collection pauses the application worker threads, causing all in-flight sockets to stall
Connect timeout too aggressive	connect timed out	Network latency, TLS negotiation overhead, or SYN queue backlog exceeds a short Connect Timeout (e.g. 500ms)
Missing timeout configuration	Hangs indefinitely	When timeouts are blank (default 0), JMeter threads wait indefinitely for dead TCP connections until the OS socket timeout triggers
Load balancer / proxy silent drop	Read timed out	Intermediate firewall or load balancer drops the idle connection without sending a TCP RST or FIN packet

Fix (ordered)

1. Differentiate Connect vs Read Timeout

• If the message is connect timed out: The failure is on the network or firewall layer before the server processed anything. Check host reachability, firewall rules, and ingress controller SYN queues.
• If the message is Read timed out: The server received the request but took too long to answer. The bottleneck is inside the application or database layer.

2. Configure Explicit Timeouts in HTTP Request Defaults

Never leave timeouts empty (0 means infinite in Java sockets). Add explicit thresholds in HTTP Request Defaults under the Timeouts (milliseconds) section:

Connect: 10000  (10 seconds)
Response: 60000 (60 seconds)

You can parameterize timeouts with properties for dynamic CLI overrides:

Connect:  ${__P(connect.timeout,10000)}
Response: ${__P(response.timeout,60000)}

# Override timeouts dynamically via CLI properties
jmeter -n -t testplan.jmx -Jconnect.timeout=5000 -Jresponse.timeout=30000 -l results.jtl -j jmeter.log

3. Inspect Server-Side APM & Slow Query Logs

When Read timed out spikes under load:

1. Check server CPU, memory, and JVM garbage collection metrics.
2. Check database connection pool utilization (HikariCP, Tomcat JDBC) and active slow queries.
3. Check downstream third-party API dependencies and external HTTP calls.

4. Verify Keep-Alive & Connection Pooling Settings

If long-running requests drop intermittently, verify keep-alive behavior in user.properties:

# Validate idle connections before reuse (milliseconds)
httpclient4.validate_after_inactivity=2000
# Connection time to live in milliseconds
httpclient4.time_to_live=60000

5. Tune OS TCP Socket Keepalive (Load Injector)

For long soak tests on Linux load generators:

# Check current TCP keepalive settings
sysctl net.ipv4.tcp_keepalive_time
sysctl net.ipv4.tcp_keepalive_intvl
sysctl net.ipv4.tcp_keepalive_probes

Related tools and topics

Resource	Use when
Non HTTP response code	Understanding generic client-side sample failures
NoHttpResponseException	Server closes socket before sending any bytes
HTTP 502/503/504	Gateway timeouts returned by reverse proxies
Thread Calculator	Calibrating concurrency against server response times
Properties Cheat Sheet	Interactive reference for JMeter core properties

Frequently asked questions

Is SocketTimeoutException a client error or server error?

connect timed out is typically a network routing, DNS, or firewall issue. Read timed out is almost always a server-side performance bottleneck where the application takes longer to calculate the response than JMeter is configured to wait.

Why does SocketTimeoutException only appear at higher concurrency?

Under light load, the server responds in 200ms. Under heavy concurrency, thread contention, database connection pool exhaustion, and CPU saturation cause response times to exceed the timeout threshold (e.g. 5000ms).

Does increasing response timeout in JMeter fix the root problem?

No. Raising the timeout merely prevents JMeter from failing the sample early. If response times breach your service level agreement (SLA), you must optimize the server code, queries, or server capacity.

Continue Learning

→

Next Practical Step

Add explicit connect and response timeouts to HTTP Request Defaults, then check server-side APM logs during the next test run.

📖

Related Reference

• API load testing
• Best practices
• Distributed testing
• Troubleshooting overview