From 55aeeb5765a12ad318fe3c72f5c14aeab075b959 Mon Sep 17 00:00:00 2001
From: Joonas Koivunen <joonas@neon.tech>
Date: Fri, 19 Jul 2024 16:08:03 +0000
Subject: [PATCH] allow deleting timeline unblock gc

---
 pageserver/src/tenant/timeline/delete.rs      |  2 ++
 .../src/tenant/timeline/detach_ancestor.rs    | 36 +++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/pageserver/src/tenant/timeline/delete.rs b/pageserver/src/tenant/timeline/delete.rs
index ab6a5f20ba..d69022143f 100644
--- a/pageserver/src/tenant/timeline/delete.rs
+++ b/pageserver/src/tenant/timeline/delete.rs
@@ -221,6 +221,8 @@ impl DeleteTimelineFlow {
         // Now that the Timeline is in Stopping state, request all the related tasks to shut down.
         timeline.shutdown(super::ShutdownMode::Hard).await;
 
+        tenant.ongoing_timeline_detach.on_delete(&timeline);
+
         fail::fail_point!("timeline-delete-before-index-deleted-at", |_| {
             Err(anyhow::anyhow!(
                 "failpoint: timeline-delete-before-index-deleted-at"
diff --git a/pageserver/src/tenant/timeline/detach_ancestor.rs b/pageserver/src/tenant/timeline/detach_ancestor.rs
index d7da944d31..284979b31b 100644
--- a/pageserver/src/tenant/timeline/detach_ancestor.rs
+++ b/pageserver/src/tenant/timeline/detach_ancestor.rs
@@ -446,6 +446,42 @@ impl SharedStateInner {
         assert!(!self.known_ongoing.is_empty());
         self.latest = Some((ExistingAttempt::ReadFromIndexPart, witnessed));
     }
+
+    fn on_delete(&mut self, timeline_id: &TimelineId) {
+        let witnessed = match self.latest.as_ref() {
+            Some((ExistingAttempt::Actual(x, barrier), witnessed)) if x == timeline_id => {
+                assert!(
+                    barrier.is_ready(),
+                    "the attempt is still ongoing; is this call happening before closing the gate?"
+                );
+                *witnessed
+            }
+            Some((ExistingAttempt::ContinuedOverRestart(x), witnessed)) if x == timeline_id => {
+                *witnessed
+            }
+            Some((ExistingAttempt::ReadFromIndexPart, witnessed))
+                if self.known_ongoing.contains(timeline_id) =>
+            {
+                *witnessed
+            }
+            _ => return,
+        };
+
+        assert!(self.known_ongoing.remove(timeline_id));
+
+        if self.known_ongoing.is_empty() {
+            self.latest = None;
+            tracing::info!("gc is now unblocked following timeline deletion");
+        } else {
+            self.latest = Some((ExistingAttempt::ReadFromIndexPart, witnessed));
+            tracing::info!(
+                n = self.known_ongoing.len(),
+                "gc is still blocked for remaining ongoing detaches"
+            );
+        }
+
+        todo!("there should be a test for this.")
+    }
 }
 
 #[derive(Debug)]