From ada91b2097c7d4ec4dff3a5264dffb07fd818a68 Mon Sep 17 00:00:00 2001
From: Christian Schwarz <christian@neon.tech>
Date: Fri, 29 Nov 2024 20:10:32 +0100
Subject: [PATCH] open time spent throttled

---
 pageserver/src/metrics.rs | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/pageserver/src/metrics.rs b/pageserver/src/metrics.rs
index 33b494f618..48a2c5f941 100644
--- a/pageserver/src/metrics.rs
+++ b/pageserver/src/metrics.rs
@@ -1427,6 +1427,25 @@ impl SmgrQueryTimePerTimeline {
     ) -> GlobalAndPerTimelineHistogramTimer<'c> {
         self.global_started[op as usize].inc();
 
+        // We subtract time spent throttled from the observed latency.
+        match ctx.micros_spent_throttled.open() {
+            Ok(()) => (),
+            Err(error) => {
+                use utils::rate_limit::RateLimit;
+                static LOGGED: Lazy<Mutex<enum_map::EnumMap<SmgrQueryType, RateLimit>>> =
+                    Lazy::new(|| {
+                        Mutex::new(enum_map::EnumMap::from_array(std::array::from_fn(|_| {
+                            RateLimit::new(Duration::from_secs(10))
+                        })))
+                    });
+                let mut guard = LOGGED.lock().unwrap();
+                let rate_limit = &mut guard[op];
+                rate_limit.call(|| {
+                    warn!(?op, error, "error opening micros_spent_throttled; this message is logged at a global rate limit");
+                });
+            }
+        }
+
         let per_timeline_latency_histo = if matches!(op, SmgrQueryType::GetPageAtLsn) {
             self.per_timeline_getpage_started.inc();
             Some(self.per_timeline_getpage_latency.clone())