add comments and fix type

src/database.rs

@@ -970,9 +970,9 @@ impl Database {
         use tokio::time::sleep;
 
         tokio::spawn(async move {
-            let mut interval: usize = 15;
+            let mut interval: u64 = 15;
 
-            const MAX_PRUNE_INTERVAL_SECS: usize = 60;
+            const MAX_PRUNE_INTERVAL_SECS: u64 = 60;
 
             loop {
                 sleep(Duration::from_secs(interval)).await;
@@ -985,6 +985,8 @@ impl Database {
                     }
                 }
 
+                // Will half the next interval if it found anything (until its 1 second)
+                // Will add one second to next interval if it didn't find anything (until its >=MAX_PRUNE_INTERVAL_SECS)
                 if pruned {
                     if interval > 1 {
                         interval /= 2;