Right query to get the current number of connections in a PostgreSQL DB

Essential queries and configurations

• Targeted pg_stat_activity query: Great for a detailed snapshot.
• Summarized pg_stat_database query: Swift count across all databases.
• max_connections: The limit of simultaneous connections.
• superuser_reserved_connections: A set number of connections reserved for superusers.
• Replication mechanisms: The role of max_wal_senders in connection count.

Summarized count for quick view

If the goal is retrieving a summary of connections, you'd use:

SELECT sum(numbackends) FROM pg_stat_database;  -- SQL: The backend story.
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Though bearing fewer rows to process, it provides a summary, lacking in insight into the specific connection states.

Deep dive: Group by state

For a richer understanding of connection states, incorporate pg_stat_activity with groupings:

SELECT state, COUNT(*) FROM pg_stat_activity GROUP BY state;  -- Like a SQL "sorting hat"!
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This displays connections grouped according to their current state, providing a more nuanced picture of the ongoing database activity.

Configurations impacting connection count

Remember, PostgreSQL configurations play a central role in controlling and understanding connections:

• max_connections: This is your capacity, your database’s version of "maximum occupancy".
• superuser_reserved_connections: These are your VIP seats, reserved for the superusers.
• max_wal_senders: This is the behind-the-scenes crew, responsible for replication connections apart from client activity.

Performance nuances

In a high-performance environment, opt for the summarized pg_stat_database view for faster results. But keep in mind, for a regular-functioning database, the performance delta between detailed and summarized views is bearly noticeable.