add prioritized cache wrapper

Signed-off-by: haoxiang47 <[email protected]>

include/titan/prioritized_cache.h

@@ -0,0 +1,35 @@
+#pragma once
+#include "rocksdb/cache.h"
+
+namespace rocksdb {
+namespace titandb {
+
+class PrioritizedCache : Cache {
+ public:
+  // Constructs a PrioritizedCache, which is a wrapper
+  // of rocksdb Cache
+  PrioritizedCache(std::shared_ptr<Cache> cache, Cache::Priority priority);
+  ~PrioritizedCache();
+
+  // Get the Cache ptr
+  std::shared_ptr<Cache> GetCache();
+
+  // always insert into the cache with the priority when init,
+  // regardless of user provided option
+  Status Insert(const Slice& key, void* value, size_t charge,
+                void (*deleter)(const Slice& key, void* value),
+                Cache::Handle** handle, Cache::Priority /*priority*/) override;
+
+ private:
+  // real insert function, it will check the cache ptr first
+  Status CheckCacheAndInsert(const Slice& key, void* value, size_t charge,
+                             void (*deleter)(const Slice& key, void* value),
+                             Cache::Handle** handle);
+
+ private:
+  std::shared_ptr<Cache> cache_;
+  Cache::Priority priority_;
+};
+
+}  // namespace titandb
+}  // namespace rocksdb

src/prioritized_cache.cc

@@ -0,0 +1,27 @@
+#include "titan/prioritized_cache.h"
+
+namespace rocksdb {
+namespace titandb {
+
+PrioritizedCache::PrioritizedCache(std::shared_ptr<Cache> cache,
+                                   Cache::Priority priority)
+    : cache_(cache), priority_(priority) {}
+
+std::shared_ptr<Cache> PrioritizedCache::GetCache() { return cache_; }
+
+Status PrioritizedCache::CheckCacheAndInsert(
+    const Slice& key, void* value, size_t charge,
+    void (*deleter)(const Slice& key, void* value), Cache::Handle** handle) {
+  if (!cache_) return Status::NotFound();
+  return cache_->Insert(key, value, charge, deleter, handle, priority_);
+}
+
+Status PrioritizedCache::Insert(const Slice& key, void* value, size_t charge,
+                                void (*deleter)(const Slice& key, void* value),
+                                Cache::Handle** handle,
+                                Cache::Priority /*priority*/) {
+  return CheckCacheAndInsert(key, value, charge, deleter, handle);
+}
+
+}  // namespace titandb
+}  // namespace rocksdb