Add support for FastLRUCache in db_bench. (#10096)

Summary:
db_bench can now run with FastLRUCache.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/10096

Test Plan:
- Temporarily add an ``assert(false)`` in the execution path that sets up the FastLRUCache. Run ``make -j24 db_bench``. Then test the appropriate code is used by running ``./db_bench -cache_type=fast_lru_cache`` and checking that the assert is called. Repeat for LRUCache.
- Verify that FastLRUCache (currently a clone of LRUCache) produces similar benchmark data than LRUCache, by comparing the outputs of ``./db_bench -benchmarks=fillseq,fillrandom,readseq,readrandom -cache_type=fast_lru_cache`` and ``./db_bench -benchmarks=fillseq,fillrandom,readseq,readrandom -cache_type=lru_cache``.

Reviewed By: gitbw95

Differential Revision: D36898774

Pulled By: guidotag

fbshipit-source-id: f9f6b6f6da124f88b21b3c8dee742fbb04eff773

tools/db_bench_tool.cc

@@ -37,6 +37,7 @@
 #include <thread>
 #include <unordered_map>
 
+#include "cache/fast_lru_cache.h"
 #include "db/db_impl/db_impl.h"
 #include "db/malloc_stats.h"
 #include "db/version_set.h"
@@ -567,8 +568,7 @@ DEFINE_double(cache_high_pri_pool_ratio, 0.0,
               "If > 0.0, we also enable "
               "cache_index_and_filter_blocks_with_high_priority.");
 
-DEFINE_bool(use_clock_cache, false,
+DEFINE_string(cache_type, "lru_cache", "Type of block cache.");
-            "Replace default LRU block cache with clock cache.");
 
 DEFINE_bool(use_compressed_secondary_cache, false,
             "Use the CompressedSecondaryCache as the secondary cache.");
@@ -2936,7 +2936,7 @@ class Benchmark {
     if (capacity <= 0) {
       return nullptr;
     }
-    if (FLAGS_use_clock_cache) {
+    if (FLAGS_cache_type == "clock_cache") {
       auto cache = NewClockCache(static_cast<size_t>(capacity),
                                  FLAGS_cache_numshardbits);
       if (!cache) {
@@ -2944,7 +2944,10 @@ class Benchmark {
         exit(1);
       }
       return cache;
-    } else {
+    } else if (FLAGS_cache_type == "fast_lru_cache") {
+      return NewFastLRUCache(static_cast<size_t>(capacity),
+                             FLAGS_cache_numshardbits);
+    } else if (FLAGS_cache_type == "lru_cache") {
       LRUCacheOptions opts(
           static_cast<size_t>(capacity), FLAGS_cache_numshardbits,
           false /*strict_capacity_limit*/, FLAGS_cache_high_pri_pool_ratio,
@@ -2993,6 +2996,9 @@ class Benchmark {
       }
 
       return NewLRUCache(opts);
+    } else {
+      fprintf(stderr, "Cache type not supported.");
+      exit(1);
     }
   }