improvement: do not send realtime only filters to the DB (limit:0)

src/server.rs

@@ -674,8 +674,10 @@ async fn nostr_server(
                                     if let Some(previous_query) = running_queries.insert(s.id.to_owned(), abandon_query_tx) {
                     previous_query.send(()).ok();
                                     }
+		                    if s.needs_historical_events() {
                                     // start a database query.  this spawns a blocking database query on a worker thread.
 					db::db_query(s, cid.to_owned(), pool.clone(), query_tx.clone(), abandon_query_rx).await;
+				    }
                 },
                 Err(e) => {
                     info!("Subscription error: {} (cid: {}, sub: {:?})", e, cid, s.id);

src/subscription.rs

@@ -200,6 +200,13 @@ impl Subscription {
     pub fn get_id(&self) -> String {
         self.id.clone()
     }
+
+    /// Determine if any filter is requesting historical (database)
+    /// queries.  If every filter has limit:0, we do not need to query the DB.
+    pub fn needs_historical_events(&self) -> bool {
+	self.filters.iter().any(|f| f.limit!=Some(0))
+    }
+
     /// Determine if this subscription matches a given [`Event`].  Any
     /// individual filter match is sufficient.
     pub fn interested_in_event(&self, event: &Event) -> bool {