From 9b71ae7dce74da148f186baa4ce185d8b7a9b06c Mon Sep 17 00:00:00 2001
From: Eric Seppanen <eds@reric.net>
Date: Wed, 21 Apr 2021 12:45:22 -0700
Subject: [PATCH] page_cache: add an assert on the last_valid_lsn

---
 pageserver/src/page_cache.rs | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/pageserver/src/page_cache.rs b/pageserver/src/page_cache.rs
index 7db50aee1f..85980b08ff 100644
--- a/pageserver/src/page_cache.rs
+++ b/pageserver/src/page_cache.rs
@@ -286,7 +286,8 @@ impl PageCache {
         let minkey = CacheKey { tag, lsn: 0 };
         let maxkey = CacheKey { tag, lsn };
 
-        if self.walreceiver_works.load(Ordering::Acquire) {
+        let walreceiver_works = self.walreceiver_works.load(Ordering::Acquire);
+        if walreceiver_works {
             self.seqwait_lsn
                 .wait_for_timeout(lsn, TIMEOUT)
                 .await
@@ -313,6 +314,10 @@ impl PageCache {
         {
             let shared = self.shared.lock().unwrap();
 
+            if walreceiver_works {
+                assert!(lsn <= shared.last_valid_lsn);
+            }
+
             if lsn < shared.first_valid_lsn {
                 bail!(
                     "LSN {:X}/{:X} has already been removed",