ORA-02063: Preceding Line from Database Link - Fix Oracle Database Link Error

ORA-02063: Preceding Line from [Database Link Name]

Error Overview

Error Text: ORA-02063: preceding line from [database_link_name]

This error appears when an error occurs on a remote database accessed through a database link, and Oracle reports both the original remote error and this ORA-02063 error indicating which database link was involved. It’s essentially a “wrapper” error that provides context about distributed database operations.

Understanding Database Links

What is a Database Link?

A database link is a connection from one Oracle database to another, allowing you to access remote objects as if they were local. Database links enable distributed database architectures and cross-database queries.

Types of Database Links

• Private Database Links: Accessible only to the user who created them
• Public Database Links: Accessible to all users in the database
• Global Database Links: Created and managed by the network domain service

Common Database Link Operations

• Remote table queries: SELECT * FROM table@remote_db
• Remote procedure calls: EXEC procedure@remote_db
• Distributed transactions across multiple databases
• Data replication and synchronization

Common Scenarios and Causes

1. Network Connectivity Issues

• Network interruption during distributed transaction
• Firewall blocking database link connections
• DNS resolution failures for remote host
• Timeout issues on slow network connections

2. Remote Database Problems

• Remote database unavailable or down
• Insufficient privileges on remote database
• Objects missing or renamed on remote database
• Remote database running out of resources

3. Authentication and Security Issues

• Invalid username/password for database link
• Account locked or expired on remote database
• Privilege changes on remote database
• SSL/TLS certificate issues in secure connections

4. Configuration Problems

• TNS configuration errors
• Database link definition errors
• Connect string issues in database link
• Oracle Net configuration problems

Diagnostic Steps

1. Identify the Remote Error”

The ORA-02063 error always accompanies another error. Look for the preceding error message which contains the actual problem:

-- Example error sequence:
ORA-00942: table or view does not exist
ORA-02063: preceding line from REMOTE_DB_LINK

2. Test Database Link Connectivity

-- Test basic connectivity
SELECT * FROM dual@database_link_name;

-- Test with a simple query
SELECT sysdate FROM dual@database_link_name;

-- Check if specific table exists
SELECT count(*) FROM user_tables@database_link_name
WHERE table_name = 'YOUR_TABLE';

3. Check Database Link Definition

-- View database link details
SELECT db_link, username, host, created
FROM user_db_links
WHERE db_link = 'DATABASE_LINK_NAME';

-- For DBA: Check all database links
SELECT * FROM dba_db_links;

4. Verify Remote Database Status

-- Check remote database availability
SELECT * FROM v$database@database_link_name;

-- Check remote instance status
SELECT instance_name, status FROM v$instance@database_link_name;

Solutions by Error Type

Solution 1: Network Connectivity Issues

# Test network connectivity
ping remote_hostname
telnet remote_hostname 1521

# Test TNS connectivity
tnsping remote_service_name

# Check firewall settings
iptables -L | grep 1521  # Linux
netsh firewall show config  # Windows

Solution 2: Authentication Problems

-- Recreate database link with correct credentials
DROP DATABASE LINK database_link_name;

CREATE DATABASE LINK database_link_name
CONNECT TO remote_username IDENTIFIED BY remote_password
USING 'remote_tns_service';

-- Test the new link
SELECT * FROM dual@database_link_name;

Solution 3: Remote Object Access Issues

-- Check if object exists on remote database
SELECT * FROM all_objects@database_link_name
WHERE object_name = 'YOUR_OBJECT';

-- Verify permissions on remote database
SELECT * FROM all_tab_privs@database_link_name
WHERE table_name = 'YOUR_TABLE';

-- Grant necessary privileges on remote database
GRANT SELECT ON schema.table_name TO remote_user;

Solution 4: Fix TNS Configuration

# Check tnsnames.ora for remote service
cat $ORACLE_HOME/network/admin/tnsnames.ora

# Verify service name resolution
tnsping remote_service_name

# Test connection manually
sqlplus username/password@remote_service_name

Advanced Troubleshooting

Check Database Link Sessions

-- View active database link sessions
SELECT * FROM v$dblink;

-- Check for hanging database link sessions
SELECT sid, serial#, username, program, machine
FROM v$session
WHERE sid IN (SELECT sid FROM v$dblink);

Monitor Distributed Transactions

-- Check for pending distributed transactions
SELECT * FROM dba_2pc_pending;

-- View distributed transaction details
SELECT local_tran_id, global_tran_id, state, mixed
FROM dba_2pc_pending;

Database Link Performance

-- Check database link usage statistics
SELECT name, gets, misses, immediate_gets, immediate_misses
FROM v$latch
WHERE name LIKE '%distributed%';

Cleanup Hanging Connections

-- Kill hanging database link sessions
ALTER SYSTEM KILL SESSION 'sid,serial#';

-- Force rollback of distributed transactions
ROLLBACK FORCE 'transaction_id';

Prevention Strategies

1. Robust Network Configuration

• Configure connection timeouts appropriately
• Implement retry logic in applications
• Use connection pooling for better resource management
• Monitor network latency and reliability

2. Database Link Best Practices

• Use descriptive database link names
• Document all database links and their purposes
• Regularly test database link connectivity
• Implement proper error handling in applications

3. Security Management

• Regularly update database link passwords
• Use wallet-based authentication when possible
• Monitor database link usage for security audits
• Implement principle of least privilege

4. Performance Optimization

• Minimize data transfer over database links
• Use local temporary tables for complex operations
• Implement proper indexing on remote tables
• Monitor and tune distributed query performance

Monitoring and Maintenance

Regular Health Checks

-- Daily database link connectivity test
SELECT db_link,
       CASE
         WHEN (SELECT COUNT(*) FROM dual@db_link) = 1
         THEN 'OK'
         ELSE 'FAILED'
       END AS status
FROM user_db_links;

Automated Monitoring

#!/bin/bash
# Script to test all database links
for link in $(sqlplus -s user/pass <<< "SELECT db_link FROM user_db_links;")
do
  echo "Testing $link..."
  sqlplus -s user/pass <<< "SELECT * FROM dual@$link;"
done

Related Errors

• ORA-12154: TNS could not resolve connect identifier
• ORA-00942: Table or view does not exist (on remote database)
• ORA-01017: Invalid username/password (on remote database)
• ORA-12545: Connect failed because target host or object does not exist
• ORA-02019: Connection description for remote database not found

Quick Reference

Emergency Response Steps

1. Identify root cause: Look for the error preceding ORA-02063
2. Test connectivity: SELECT * FROM dual@database_link;
3. Check credentials: Verify username/password on remote database
4. Validate configuration: Check TNS and database link definitions

Quick Commands

-- Essential diagnostic queries
SELECT * FROM user_db_links;
SELECT * FROM v$dblink;
SELECT * FROM dba_2pc_pending;
tnsping remote_service_name;

Troubleshooting Checklist

• Remote database is running and accessible
• Network connectivity is working
• Database link credentials are correct
• Required privileges exist on remote database
• TNS configuration is correct
• No firewall blocking connections