From 3504ce97ef3136f57afa1921fd8f9f7b6c6475dc Mon Sep 17 00:00:00 2001
From: Marcus Holland-Moritz <github@mhxnet.de>
Date: Thu, 14 Nov 2024 11:14:55 +0100
Subject: [PATCH] fix(block_cache): skip prefetch if the block is already
 cached

---
 src/reader/internal/block_cache.cpp | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/reader/internal/block_cache.cpp b/src/reader/internal/block_cache.cpp
index 8306c1a0..8667dacc 100644
--- a/src/reader/internal/block_cache.cpp
+++ b/src/reader/internal/block_cache.cpp
@@ -385,10 +385,10 @@ class block_cache_ final : public block_cache::impl {
 
     scope_exit do_prefetch{[&] {
       if (auto next = seq_access_detector_->prefetch()) {
-        sequential_prefetches_.fetch_add(1, std::memory_order_relaxed);
+        std::lock_guard lock(mx_);
 
-        {
-          std::lock_guard lock(mx_);
+        if (cache_.findWithoutPromotion(*next) == cache_.end()) {
+          sequential_prefetches_.fetch_add(1, std::memory_order_relaxed);
           create_cached_block(*next, std::promise<block_range>{}, 0,
                               std::numeric_limits<size_t>::max());
         }