What are the optimal connection settings for combining pgpool-4.4.0 and PostgreSQL-12.5?

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The optimal connection settings for combining pgpool-4.4.0 and PostgreSQL-12.5 depend on several factors, such as the size of the database, the available hardware resources, and the expected traffic volume. However, there are some general guidelines that can help optimize the performance and stability of the system:

1. Connection pool settings: Pgpool has several parameters that control the behavior of the connection pool. To optimize the resource usage and avoid overloading the database, you should adjust the following settings:
2. numinitchildren: This parameter controls the number of pre-forked child processes that handle the client connections. The recommended value is 32-64, but you can increase or decrease it based on your hardware resources and expected workload.
3. max_pool: This parameter limits the maximum number of client connections that can be pooled. If you have a large database or a high traffic volume, you may need to increase this value to avoid connection timeouts or errors.

4. idle_timeout: This parameter defines the time (in seconds) after which an idle connection is closed. The default value is 600 (10 minutes), but you may want to reduce it if you have a lot of short-lived connections or increase it if you have long-running transactions.

5. PostgreSQL connection settings: Additionally, you should configure the PostgreSQL server to optimize the connection handling and avoid resource contention. Some recommended parameters are:

6. max_connections: This parameter sets the maximum number of concurrent connections that PostgreSQL can accept. You should set it to a value that matches the number of connections that pgpool can handle to avoid bottlenecks and performance issues.
7. shared_buffers: This parameter controls the amount of memory that PostgreSQL uses for caching data. You should set it to a value that matches the available RAM on the server and the size of the database.

8. work_mem: This parameter defines the amount of memory that PostgreSQL uses for sorting and other processing operations. You should set it to a value that matches the size of the queries and the available RAM on the server.

9. Network settings: Finally, you should adjust the network settings to optimize the throughput and latency of the system. Some recommended settings are:

10. tcpkeepalivesidle: This parameter defines the time (in seconds) after which a TCP connection is closed if there is no activity. You can set it to a low value (e.g., 60) to avoid stale connections or increase it if you have long-running transactions.
11. tcpkeepalivesinterval: This parameter defines the time (in seconds) between sending TCP keepalive messages. You can set it to a low value (e.g., 5) to detect connection problems more quickly.
12. tcpkeepalivescount: This parameter defines the number of TCP keepalive messages that can be sent without a response before the connection is closed. You can set it to a high value (e.g., 10) to avoid false positives and unnecessary connection resets.