From 0053ccac134136d56bea7b447d5f6bd2906223b3 Mon Sep 17 00:00:00 2001
From: Bojan Serafimov <bojan.serafimov7@gmail.com>
Date: Mon, 12 Dec 2022 13:48:54 -0500
Subject: [PATCH] Add live correctness comparison

---
 pageserver/src/tenant/layer_map.rs | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/pageserver/src/tenant/layer_map.rs b/pageserver/src/tenant/layer_map.rs
index 954afa0c7e..12eb65e162 100644
--- a/pageserver/src/tenant/layer_map.rs
+++ b/pageserver/src/tenant/layer_map.rs
@@ -248,8 +248,23 @@ impl LayerMap {
     /// layer.
     ///
     pub fn search(&self, key: Key, end_lsn: Lsn) -> Result<Option<SearchResult>> {
-        // HACK use the index to query and return early. If this works I'll
-        //      rewrite the function.
+        let old = self.search_old(key, end_lsn)?;
+        let new = self.search_new(key, end_lsn)?;
+        match (&old, &new) {
+            (None, None) => {}
+            (None, Some(_)) => panic!("returned Some, expected None"),
+            (Some(_), None) => panic!("returned None, expected Some"),
+            (Some(old), Some(new)) => {
+                // TODO be more verbose and flexible
+                assert_eq!(old.layer.filename(), new.layer.filename());
+                assert_eq!(old.lsn_floor, new.lsn_floor);
+            }
+        }
+        return Ok(new);
+    }
+
+    // HACK just testing correctness
+    fn search_new(&self, key: Key, end_lsn: Lsn) -> Result<Option<SearchResult>> {
         // TODO I'm making two separate queries, which is 2x the cost, but that
         //      can be avoided in varous ways. Caching latest_image queries is
         //      probably the simplest, but combining the two data structures
@@ -269,7 +284,10 @@ impl LayerMap {
                 lsn_floor,
             }
         }));
+    }
 
+    // HACK just testing correctness
+    fn search_old(&self, key: Key, end_lsn: Lsn) -> Result<Option<SearchResult>> {
         // linear search
         // Find the latest image layer that covers the given key
         let mut latest_img: Option<Arc<dyn Layer>> = None;