To troubleshoot performance issues in streaming replication with PostgreSQL, follow these steps to configure it properly. This will allow you to monitor and diagnose any problems that may occur effectively. Here is a step-by-step guide:

Step 1: Enable Detailed Logging

1. Edit postgresql.conf on both Primary and Standby Servers:
   • log_min_duration_statement: Set this to log queries taking more than a certain amount of time (e.g., 1000 for 1 second). This helps in identifying slow queries.
   • log_checkpoints: Set to on. This will log checkpoint information, which is crucial for performance analysis.
   • log_connections and log_disconnections: Set these to on to track client connections and disconnections.
   • log_replication_commands: Set to on to log replication-specific commands.
   • log_lock_waits: Set to on to log information about locks that are waited on for more than deadlock_timeout.
2. Set Up Appropriate Log Destination:
   • logging_collector: Set to on to enable the logging collector.
   • log_directory and log_filename: Configure these to determine where logs are stored and their naming convention.

Step 2: Monitor Replication Lag

1. Use Built-in Functions:
   • On the Primary, use pg_stat_replication to view the status of the replication processes.
   • On the Standby, use pg_stat_wal_receiver to see the status of the WAL receiver process.
2. Check Replication Lag:
   • Compare the write_lsn or flush_lsn of the primary with the received_lsn or replay_lsn of the standby. The difference indicates replication lag.

Step 3: Monitor System and Network Performance

1. System Monitoring Tools:
   • Use tools like htop, iostat, or vmstat to monitor CPU, memory, and I/O usage.
   • Check for any resource bottlenecks that might affect replication performance.
2. Network Monitoring:
   • Use tools like ping, netstat, or iperf to check network connectivity and throughput between the primary and standby servers.

Step 4: Analyze WAL Generation and Transmission

1. WAL Generation Rate:
   • On the primary, monitor the rate at which WAL files are being generated. A high rate could indicate heavy write activity.
2. WAL Transmission:
   • Ensure that WAL segments are being transmitted efficiently to the standby. Delays or interruptions could cause lag.

Step 5: Use Extensions and Tools for Advanced Monitoring

1. pg_stat_statements:
   • Install and enable pg_stat_statements to collect statistics on executed SQL statements, which is useful for identifying slow queries.
2. pgBadger:
   • Use pgBadger to analyze PostgreSQL logs for detailed performance reports.
3. External Monitoring Tools:
   • Consider using external monitoring tools like Grafana with Prometheus, or a PostgreSQL-specific tool like pganalyze for more in-depth analysis.

Step 6: Regularly Review and Adjust Configuration

• Regularly review the performance metrics and adjust your PostgreSQL configuration as needed.
• Consider increasing resources or optimizing queries based on the findings.

Conclusion

To troubleshoot performance issues in PostgreSQL streaming replication, a comprehensive approach is needed. This includes enabling detailed logging, regularly monitoring replication lag, analyzing system and network performance, and utilizing advanced monitoring tools. It is important to regularly review and make adjustments based on the gathered data to maintain an efficient and reliable replication setup.