adapter: Add 'start time' to SHOW READYSET STATUS

Add the start time of the adapter to the output of
SHOW READYSET STATUS.

Fixes: REA-3321
Release-Note-Core: ReadySet will display the process start time in
  SHOW READYSET SATAUS if `--prometheus-metrics` is enabled.

Change-Id: I5e9810a73551ff7ecc3b0a554de4e493a09fef8e
Reviewed-on: https://gerrit.readyset.name/c/readyset/+/6076
Tested-by: Buildkite CI
Reviewed-by: Tamas Juhasz <tamas@readyset.io>

readyset-adapter/src/backend.rs

@@ -1969,7 +1969,7 @@ where
             }
             SqlQuery::Show(ShowStatement::ReadySetStatus) => {
                 // Add upstream connectivity status
-                let additional_meta = if let Some(upstream) = &mut self.upstream {
+                let mut additional_meta = if let Some(upstream) = &mut self.upstream {
                     let connection_status = upstream
                         .is_connected()
                         .await
@@ -1980,6 +1980,11 @@ where
                     vec![]
                 };
 
+                if let Some(handle) = self.metrics_handle.as_ref() {
+                    let mut statuses = handle.readyset_status();
+                    additional_meta.append(&mut statuses);
+                }
+
                 self.noria
                     .readyset_status(&self.authority, additional_meta)
                     .await

readyset-adapter/src/metrics_handle.rs

@@ -5,6 +5,8 @@ use metrics_exporter_prometheus::formatting::{sanitize_label_key, sanitize_label
 use metrics_exporter_prometheus::{Distribution, PrometheusHandle};
 use metrics_util::Summary;
 use quanta::Instant;
+// adding an alias to disambiguate vs readyset_client_metrics::recorded
+use readyset_client::metrics::recorded as client_recorded;
 use readyset_client_metrics::recorded::QUERY_LOG_EXECUTION_TIME;
 
 #[derive(Debug, Default, Clone)]
@@ -106,4 +108,29 @@ impl MetricsHandle {
             p99_us: summary.quantile(0.99).unwrap_or_default(),
         })
     }
+
+    fn sum_counter(&self, name: &str) -> u64 {
+        let results = self.counters(Some(|x: &str| x.eq(name)));
+        match results.get(name) {
+            Some(res) => {
+                let mut f = 0;
+                for (_, v) in res.iter() {
+                    f += v;
+                }
+                f
+            }
+            None => 0,
+        }
+    }
+
+    /// Gather all the metrics that are relevant to be printed with
+    /// `SHOW READYSET STATUS`
+    pub fn readyset_status(&self) -> Vec<(String, String)> {
+        let mut statuses = Vec::new();
+
+        let val = self.sum_counter(client_recorded::NORIA_STARTUP_TIMESTAMP);
+        statuses.push(("Process start time".to_string(), val.to_string()));
+
+        statuses
+    }
 }