Fork and simplify LRUCache for developing enhancements (facebook#9917)

Summary:
To support a project to prototype and evaluate algorithmic
enhancments and alternatives to LRUCache, here I have separated out
LRUCache into internal-only "FastLRUCache" and cut it down to
essentials, so that details like secondary cache handling and
priorities do not interfere with prototyping. These can be
re-integrated later as needed, along with refactoring to minimize code
duplication (which would slow down prototyping for now).

Pull Request resolved: facebook#9917

Test Plan:
unit tests updated to ensure basic functionality has (likely)
been preserved

Reviewed By: anand1976

Differential Revision: D35995554

Pulled By: pdillinger

fbshipit-source-id: d67b20b7ada3b5d3bfe56d897a73885894a1d9db

CMakeLists.txt

@@ -596,6 +596,7 @@ set(SOURCES
         cache/cache_reservation_manager.cc
         cache/clock_cache.cc
         cache/compressed_secondary_cache.cc
+        cache/fast_lru_cache.cc
         cache/lru_cache.cc
         cache/sharded_cache.cc
         db/arena_wrapped_db_iter.cc

TARGETS

@@ -15,6 +15,7 @@ cpp_library_wrapper(name="rocksdb_lib", srcs=[
         "cache/cache_reservation_manager.cc",
         "cache/clock_cache.cc",
         "cache/compressed_secondary_cache.cc",
+        "cache/fast_lru_cache.cc",
         "cache/lru_cache.cc",
         "cache/sharded_cache.cc",
         "db/arena_wrapped_db_iter.cc",
@@ -335,6 +336,7 @@ cpp_library_wrapper(name="rocksdb_whole_archive_lib", srcs=[
         "cache/cache_reservation_manager.cc",
         "cache/clock_cache.cc",
         "cache/compressed_secondary_cache.cc",
+        "cache/fast_lru_cache.cc",
         "cache/lru_cache.cc",
         "cache/sharded_cache.cc",
         "db/arena_wrapped_db_iter.cc",

cache/cache_test.cc

@@ -14,7 +14,9 @@
 #include <iostream>
 #include <string>
 #include <vector>
+
 #include "cache/clock_cache.h"
+#include "cache/fast_lru_cache.h"
 #include "cache/lru_cache.h"
 #include "test_util/testharness.h"
 #include "util/coding.h"
@@ -39,6 +41,7 @@ static int DecodeValue(void* v) {
 
 const std::string kLRU = "lru";
 const std::string kClock = "clock";
+const std::string kFast = "fast";
 
 void dumbDeleter(const Slice& /*key*/, void* /*value*/) {}
 
@@ -83,6 +86,9 @@ class CacheTest : public testing::TestWithParam<std::string> {
     if (type == kClock) {
       return NewClockCache(capacity);
     }
+    if (type == kFast) {
+      return NewFastLRUCache(capacity);
+    }
     return nullptr;
   }
 
@@ -103,6 +109,10 @@ class CacheTest : public testing::TestWithParam<std::string> {
       return NewClockCache(capacity, num_shard_bits, strict_capacity_limit,
                            charge_policy);
     }
+    if (type == kFast) {
+      return NewFastLRUCache(capacity, num_shard_bits, strict_capacity_limit,
+                             charge_policy);
+    }
     return nullptr;
   }
 
@@ -838,11 +848,13 @@ TEST_P(CacheTest, GetChargeAndDeleter) {
 std::shared_ptr<Cache> (*new_clock_cache_func)(
     size_t, int, bool, CacheMetadataChargePolicy) = NewClockCache;
 INSTANTIATE_TEST_CASE_P(CacheTestInstance, CacheTest,
-                        testing::Values(kLRU, kClock));
+                        testing::Values(kLRU, kClock, kFast));
 #else
-INSTANTIATE_TEST_CASE_P(CacheTestInstance, CacheTest, testing::Values(kLRU));
+INSTANTIATE_TEST_CASE_P(CacheTestInstance, CacheTest,
+                        testing::Values(kLRU, kFast));
 #endif  // SUPPORT_CLOCK_CACHE
-INSTANTIATE_TEST_CASE_P(CacheTestInstance, LRUCacheTest, testing::Values(kLRU));
+INSTANTIATE_TEST_CASE_P(CacheTestInstance, LRUCacheTest,
+                        testing::Values(kLRU, kFast));
 
 }  // namespace ROCKSDB_NAMESPACE