From d6cdf1b13f7f81faac636fd4404edd36ccbb857b Mon Sep 17 00:00:00 2001
From: Christian Schwarz <christian@neon.tech>
Date: Tue, 21 Jan 2025 20:21:35 +0100
Subject: [PATCH] debug assertion on correct record order:
 https://github.com/neondatabase/neon/pull/9353#discussion_r1923801121

---
 pageserver/src/tenant/timeline.rs | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/pageserver/src/tenant/timeline.rs b/pageserver/src/tenant/timeline.rs
index d7aa9a478b..68ab597551 100644
--- a/pageserver/src/tenant/timeline.rs
+++ b/pageserver/src/tenant/timeline.rs
@@ -1206,6 +1206,15 @@ impl Timeline {
                         }
                     };
 
+                    // The walredo module expects the records to be descending in terms of Lsn.
+                    // And we submit the IOs in that order, so, there shuold be no need to sort here.
+                    debug_assert!(
+                        converted
+                            .records
+                            .is_sorted_by_key(|(lsn, _)| std::cmp::Reverse(*lsn)),
+                        "{converted:?}"
+                    );
+
                     (
                         key,
                         walredo_self.reconstruct_value(key, lsn, converted).await,