From c11c19d5681a3c78464a3a40f6cbb453d98a5525 Mon Sep 17 00:00:00 2001
From: Bojan Serafimov <bojan.serafimov7@gmail.com>
Date: Mon, 12 Dec 2022 20:25:24 -0500
Subject: [PATCH] Check for exact match

---
 pageserver/src/tenant/bst_layer_map.rs |  4 ----
 pageserver/src/tenant/layer_map.rs     | 12 ++++++++++++
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/pageserver/src/tenant/bst_layer_map.rs b/pageserver/src/tenant/bst_layer_map.rs
index fb245c2eae..0ed62c4ec0 100644
--- a/pageserver/src/tenant/bst_layer_map.rs
+++ b/pageserver/src/tenant/bst_layer_map.rs
@@ -55,8 +55,6 @@ impl<Value: Clone> PersistentLayerMap<Value> {
     }
 
     pub fn insert(self: &mut Self, key: Range<i128>, lsn: Range<u64>, value: Value) {
-        // TODO check for off-by-one errors
-
         // It's only a persistent map, not a retroactive one
         if let Some(last_entry) = self.historic.iter().rev().next() {
             let last_lsn = last_entry.0;
@@ -112,8 +110,6 @@ impl<Value: Clone> PersistentLayerMap<Value> {
     }
 
     pub fn query(self: &Self, key: i128, lsn: u64) -> Option<Value> {
-        // TODO check for off-by-one errors
-
         let version = self.historic.range(0..=lsn).rev().next()?.1;
         version
             .range(0..=key)
diff --git a/pageserver/src/tenant/layer_map.rs b/pageserver/src/tenant/layer_map.rs
index b3ba7c502b..7fd65d2215 100644
--- a/pageserver/src/tenant/layer_map.rs
+++ b/pageserver/src/tenant/layer_map.rs
@@ -272,6 +272,18 @@ impl LayerMap {
         //      might be better.
         let latest_layer = self.index.query(key.to_i128(), end_lsn.0 - 1);
         let latest_image = self.images.query(key.to_i128(), end_lsn.0 - 1);
+
+        // Check for exact match
+        if let Some(image) = &latest_image {
+            let img_lsn = image.get_lsn_range().start;
+            if Lsn(img_lsn.0 + 1) == end_lsn {
+                return Ok(Some(SearchResult {
+                    layer: Arc::clone(&image),
+                    lsn_floor: img_lsn,
+                }));
+            }
+        }
+
         return Ok(latest_layer.map(|layer| {
             // Compute lsn_floor
             let mut lsn_floor = layer.get_lsn_range().start;