Print the block cache size in the LOG.

Summary: Print the block cache size in the LOG.

Test Plan: run db_bench and look at LOG. This is helpful while I was debugging one use-case.

Reviewers: heyongqiang, MarkCallaghan

Reviewed By: heyongqiang

Differential Revision: https://reviews.facebook.net/D5739

include/leveldb/cache.h

@@ -82,6 +82,9 @@ class Cache {
   // its cache keys.
   virtual uint64_t NewId() = 0;
 
+  // returns the maximum configured capacity of the cache
+  virtual size_t GetCapacity() = 0;
+
  private:
   void LRU_Remove(Handle* e);
   void LRU_Append(Handle* e);

util/cache.cc

@@ -276,6 +276,7 @@ class ShardedLRUCache : public Cache {
   port::Mutex id_mutex_;
   uint64_t last_id_;
   int numShardBits;
+  size_t capacity_;
 
   static inline uint32_t HashSlice(const Slice& s) {
     return Hash(s.data(), s.size(), 0);
@@ -287,6 +288,7 @@ class ShardedLRUCache : public Cache {
 
   void init(size_t capacity, int numbits) {
     numShardBits = numbits;
+    capacity_ = capacity;
     int numShards = 1 << numShardBits;
     shard_ = new LRUCache[numShards];
     const size_t per_shard = (capacity + (numShards - 1)) / numShards;
@@ -329,6 +331,9 @@ class ShardedLRUCache : public Cache {
     MutexLock l(&id_mutex_);
     return ++(last_id_);
   }
+  virtual uint64_t GetCapacity() {
+    return capacity_;
+  }
 };
 
 }  // end anonymous namespace

util/options.cc

@@ -7,6 +7,7 @@
 #include "leveldb/comparator.h"
 #include "leveldb/env.h"
 #include "leveldb/filter_policy.h"
+#include "leveldb/cache.h"
 
 namespace leveldb {
 
@@ -56,6 +57,7 @@ Options::Dump(
     Log(log,"     Options.write_buffer_size: %zd", write_buffer_size);
     Log(log,"        Options.max_open_files: %d", max_open_files);
     Log(log,"           Options.block_cache: %p", block_cache);
+    Log(log,"      Options.block_cache_size: %zd", block_cache->GetCapacity());
     Log(log,"            Options.block_size: %zd", block_size);
     Log(log,"Options.block_restart_interval: %d", block_restart_interval);
     Log(log,"           Options.compression: %d", compression);