From a7d8eaba540ce272bc4fc19afdeae177a3b086d9 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <eelco.dolstra@logicblox.com>
Date: Fri, 15 Apr 2016 15:25:15 +0200
Subject: [PATCH] BinaryCacheStore: Do negative caching of .narinfo lookups

---
 src/libstore/binary-cache-store.cc | 12 ++++++++++--
 src/libstore/binary-cache-store.hh |  3 ++-
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/src/libstore/binary-cache-store.cc b/src/libstore/binary-cache-store.cc
index 7c8fdfd08..7016eedfa 100644
--- a/src/libstore/binary-cache-store.cc
+++ b/src/libstore/binary-cache-store.cc
@@ -114,14 +114,22 @@ NarInfo BinaryCacheStore::readNarInfo(const Path & storePath)
         auto res = state_->narInfoCache.get(storePath);
         if (res) {
             stats.narInfoReadAverted++;
+            if (!*res)
+                throw InvalidPath(format("path ‘%s’ is not valid") % storePath);
             return **res;
         }
     }
 
     auto narInfoFile = narInfoFileFor(storePath);
     auto data = getFile(narInfoFile);
-    if (!data)
+    if (!data) {
+        stats.narInfoMissing++;
+        auto state_(state.lock());
+        state_->narInfoCache.upsert(storePath, 0);
+        stats.narInfoCacheSize = state_->narInfoCache.size();
         throw InvalidPath(format("path ‘%s’ is not valid") % storePath);
+    }
+
     auto narInfo = make_ref<NarInfo>(*data, narInfoFile);
     if (narInfo->path != storePath)
         throw Error(format("NAR info file for store path ‘%1%’ does not match ‘%2%’") % narInfo->path % storePath);
@@ -149,7 +157,7 @@ bool BinaryCacheStore::isValidPath(const Path & storePath)
         auto res = state_->narInfoCache.get(storePath);
         if (res) {
             stats.narInfoReadAverted++;
-            return true;
+            return *res != 0;
         }
     }
 
diff --git a/src/libstore/binary-cache-store.hh b/src/libstore/binary-cache-store.hh
index 55bba6278..dcf06b3d1 100644
--- a/src/libstore/binary-cache-store.hh
+++ b/src/libstore/binary-cache-store.hh
@@ -24,7 +24,7 @@ private:
 
     struct State
     {
-        LRUCache<Path, ref<NarInfo>> narInfoCache{32 * 1024};
+        LRUCache<Path, std::shared_ptr<NarInfo>> narInfoCache{32 * 1024};
     };
 
     Sync<State> state;
@@ -51,6 +51,7 @@ public:
     {
         std::atomic<uint64_t> narInfoRead{0};
         std::atomic<uint64_t> narInfoReadAverted{0};
+        std::atomic<uint64_t> narInfoMissing{0};
         std::atomic<uint64_t> narInfoWrite{0};
         std::atomic<uint64_t> narInfoCacheSize{0};
         std::atomic<uint64_t> narRead{0};