KB-1431 "Unable to acquire a Read/Write connection. Safe to retry."

Symptoms

At least once of the following messages in seen in the application server log:

ERROR com.appiancorp.kougar.driver.ipc.IpcConnection - Failure to read socket: process-analytics0 (<HOSTNAME>:5018)
ERROR com.appiancorp.kougar.driver.ipc.IpcConnection - Failure to read socket: process-analytics1 (<HOSTNAME>:5020)
ERROR com.appiancorp.kougar.driver.ipc.IpcConnection - Failure to read socket: process-analytics2 (<HOSTNAME>:5022)
ERROR com.appiancorp.kougar.driver.ipc.IpcConnection - Failure to read socket: process-execution0 (<HOSTNAME>:5024)
ERROR com.appiancorp.kougar.driver.ipc.IpcConnection - Failure to read socket: process-execution1 (<HOSTNAME>:5026)
ERROR com.appiancorp.kougar.driver.ipc.IpcConnection - Failure to read socket: process-execution2 (<HOSTNAME>:5028)
ERROR com.appiancorp.kougar.driver.ipc.IpcConnection - Failure to read socket: personalization (<HOSTNAME>:5012)
ERROR com.appiancorp.kougar.driver.ipc.IpcConnection - Failure to read socket: portal (<HOSTNAME>:5014)
ERROR com.appiancorp.kougar.driver.ipc.IpcConnection - Failure to read socket: process-design (<HOSTNAME>:5016)
ERROR com.appiancorp.kougar.driver.ipc.IpcConnection - Failure to read socket: content (<HOSTNAME>:5008)
ERROR com.appiancorp.kougar.driver.ipc.IpcConnection - Failure to read socket: collaboration-statistics (<HOSTNAME>:5010)
ERROR com.appiancorp.kougar.driver.ipc.IpcConnection - Failure to read socket: notify (<HOSTNAME>:5002)
ERROR com.appiancorp.kougar.driver.ipc.IpcConnection - Failure to read socket: notify-email (<HOSTNAME>:5004)
ERROR com.appiancorp.kougar.driver.ipc.IpcConnection - Failure to read socket: content (<HOSTNAME>:5008)
ERROR com.appiancorp.kougar.driver.ipc.IpcConnection - Failure to read socket: channels (<HOSTNAME>:5006)
ERROR com.appiancorp.kougar.driver.ipc.IpcConnection - Failure to read socket: forums (<HOSTNAME>:5000)

com.appiancorp.kougar.driver.exceptions.SafeRetryException: Unable to acquire a Read connection. Safe to retry.

com.appiancorp.kougar.driver.exceptions.SafeRetryException: Unable to acquire a Write connection. Safe to retry.

Cause

This message indicates that the application server sent a request to a particular engine, but did not receive a response within an acceptable time frame. When this error is encountered, it may mean the engine is busy at that time, or that the application server was unable to connect to the engine.

Action

1. To check the responsiveness, availability, and status of the Appian engine servers, run the appropriate script based on the Appian version.

   Appian 17.2 and prior

   Run the checkengine script to diagnose any potential engine related issues and work to resolve them based on the documentation: <APPIAN_HOME>/server/_scripts/diagnostic/checkengine.bat|.sh.

   Appian 17.3 and above

   Run the status script to diagnose any potential engine related issues and work to resolve them based on the documentation: <APPIAN_HOME>/services/bin/status.bat|.sh.
   
   

2. If the engines are up and running without any issues, the error message is simply indicating that the particular request could not be handled at the time because the engine is busy processing work. The request will be retried again once resources are freed up. Review the performance logs from the time that the error was encountered to see if there was an unusually high load on the system. 
3. If the application server and engines are not running on the same server, check that the appian-topology.xml is consistent across all servers.

Affected Versions

This article applies to all versions of Appian.

Last Reviewed: September 2019