Don't suspend compute if there is active LR subscriber.

https://github.com/neondatabase/neon/issues/6258

compute_tools/src/monitor.rs

@@ -3,7 +3,7 @@ use std::{thread, time::Duration};
 
 use chrono::{DateTime, Utc};
 use postgres::{Client, NoTls};
-use tracing::{debug, info};
+use tracing::{debug, info, warn};
 
 use crate::compute::ComputeNode;
 
@@ -84,6 +84,29 @@ fn watch_compute_activity(compute: &ComputeNode) {
                     }
                 }
 
+                // If there are existing (logical) walsenders, do not suspend.
+                //
+                // walproposer doesn't currently show up in pg_stat_replication,
+                // but protect if it will be
+                let ws_count_query = "select count(*) from pg_stat_replication where application_name != 'walproposer';";
+                match cli.query_one(ws_count_query, &[]) {
+                    Ok(r) => match r.try_get::<&str, i64>("count") {
+                        Ok(num_ws) => {
+                            if num_ws > 0 {
+                                last_active = Some(Utc::now());
+                            }
+                        }
+                        Err(e) => {
+                            warn!("failed to parse ws count: {:?}", e);
+                            continue;
+                        }
+                    },
+                    Err(e) => {
+                        warn!("failed to get list of walsenders: {:?}", e);
+                        continue;
+                    }
+                }
+
                 // Update the last activity in the shared state if we got a more recent one.
                 let mut state = compute.state.lock().unwrap();
                 // NB: `Some(<DateTime>)` is always greater than `None`.