Troubleshooting Oracle Dispatchers involves diagnosing issues related to performance, connectivity, or server processes. Dispatchers are crucial for routing client requests to shared server processes, and any issues with Dispatcher config can affect overall database performance and client access. Below is a detailed guide on how to troubleshoot Oracle Dispatchers, including common issues and solutions.
1. Dispatcher Process Not Starting
Symptoms:
The Dispatcher process does not appear to be running.
Errors in the log files related to the Dispatcher process (e.g., ORA-12500: TNS:listener failed to start a dedicated server process).
Where to Look:
Listener Logs: Check the Oracle Listener log (listener.log) for errors related to Dispatcher processes.
Database Alert Log: Check the database alert log for any errors related to process startup or configuration.
V$DISPATCHER View: Query the V$DISPATCHER view to check if the Dispatchers are registered with the database.
Common Causes and Solutions: Listener Configuration Issue: Ensure that the listener.ora file is correctly configured and the listener is running.
Incorrect DISPATCHERS Parameter: Double-check the DISPATCHERS parameter in spfile.ora or init.ora for any syntax errors or incorrect configurations.
Example of a correct entry:
DISPATCHERS = '(PROTOCOL=TCP)(SERVICE=orcl)(DISPATCHERS=4)'
2. Dispatcher is Overloaded or Not Handling Requests Efficiently
Symptoms:
High CPU usage by Dispatcher processes.
Slow client responses or timeout issues.
Clients experience delays in receiving responses due to Dispatcher bottlenecks.
Where to Look:
SELECT * FROM V$DISPATCHER; To monitor the number of active Dispatcher processes and their load.
SELECT * FROM V$SHARED_SERVER;Check for an imbalance between Dispatchers and shared servers.
Check if sessions are waiting for Dispatchers to process requests.
SELECT SID, SERIAL#, STATUS, EVENT FROM V$SESSION WHERE EVENT LIKE 'dispatcher%';
Common Causes and Solutions:
Insufficient Dispatchers: If there are more requests than available Dispatchers, they will queue up, causing delays. Increase the number of Dispatchers using the ALTER SYSTEM command.
ALTER SYSTEM SET DISPATCHERS = '(PROTOCOL=TCP)(SERVICE=orcl)(DISPATCHERS=6)' SCOPE=BOTH;
Imbalance Between Dispatchers and Shared Servers: Check if there are enough shared server processes to handle the incoming requests. Adjust the SHARED_SERVERS parameter accordingly.
ALTER SYSTEM SET SHARED_SERVERS=10 SCOPE=BOTH;
3. Clients Cannot Connect to the Database (ORA-12500, ORA-12545, ORA-12514 Errors)
Symptoms:Clients cannot establish a connection to the database.
Errors like:
ORA-12500: TNS:listener failed to start a dedicated server process
ORA-12545: Connect failed because target host or object does not exist
ORA-12514: TNS:listener does not currently know of service requested in connect descriptor.
Check Listener Log: Look for any connection or listener-related errors in the listener log & Alert Log
Common Causes and Solutions: Listener Not Running or Misconfigured: Ensure the listener is up and properly configured. Restart the listener and ensure the correct service is registered.
Incorrect SERVICE_NAME or SID: Verify that the SERVICE_NAME or SID specified in the tnsnames.ora file or connection string is correct.
Listener Unable to Start Shared Server: Ensure that the listener is correctly configured to handle shared server processes. In the listener.ora file, ensure the SID_LIST includes the shared server configurations.
4. Dispatcher Hanging or Not Responding to Client Requests (ORA-12535)
Symptoms:
Clients experience long delays or timeouts while waiting for responses from the Dispatcher.
Errors like ORA-12535: TNS:operation timed out or client hangs.
Common Causes and Solutions:
Network Issues: Check for network latency or firewalls blocking communication between clients and Dispatchers. Use network diagnostic tools like ping or traceroute to verify the path.
Increase Timeout: Increase the timeout values for client connections and Dispatchers to allow more time for processing.
Adjust the SQLNET.INBOUND_CONNECT_TIMEOUT parameter if necessary.
ALTER SYSTEM SET SQLNET.INBOUND_CONNECT_TIMEOUT=180;
Dispatcher Load: Check if Dispatchers are overloaded and adjust the number of Dispatchers or shared servers as needed.
5. Poor Performance or Latency in Dispatcher Handling
Symptoms:
Slower performance during peak usage times.
Latency in query processing or client response time.
Common Causes and Solutions:
Increase Dispatcher or Shared Server Processes: Increase the number of Dispatchers if the load is high.
ALTER SYSTEM SET DISPATCHERS = '(PROTOCOL=TCP)(SERVICE=orcl)(DISPATCHERS=8)' SCOPE=BOTH;
Review System Resources: Ensure the system has enough CPU, memory, and disk space for the expected load. Overutilization of system resources can cause slow response times.
Review Execution Plans: Slow queries can cause delays in processing. Use SQL Trace and Explain Plan to identify and optimize slow queries.
6. General Connection Issues (ORA-12170, ORA-12541)
Symptoms:
Clients fail to connect and report network-related errors like ORA-12170: TNS:Connect timeout occurred or ORA-12541: TNS:no listener.
Common Causes and Solutions: Listener Configuration: Ensure that the listener is properly configured and the required services are registered. Restart the listener to fix any issues.
Network Configuration: Ensure there are no firewall or network configuration issues preventing the client from reaching the database server.
