allow updating block cache capacity from C (#1149)

db/c.cc

@@ -2173,6 +2173,10 @@ void rocksdb_cache_destroy(rocksdb_cache_t* cache) {
   delete cache;
 }
 
+void rocksdb_cache_set_capacity(rocksdb_cache_t* cache, size_t capacity) {
+  cache->rep->SetCapacity(capacity);
+}
+
 rocksdb_env_t* rocksdb_create_default_env() {
   rocksdb_env_t* result = new rocksdb_env_t;
   result->rep = Env::Default();

include/rocksdb/c.h

@@ -847,6 +847,8 @@ extern ROCKSDB_LIBRARY_API void rocksdb_flushoptions_set_wait(
 extern ROCKSDB_LIBRARY_API rocksdb_cache_t* rocksdb_cache_create_lru(
     size_t capacity);
 extern ROCKSDB_LIBRARY_API void rocksdb_cache_destroy(rocksdb_cache_t* cache);
+extern ROCKSDB_LIBRARY_API void rocksdb_cache_set_capacity(
+    rocksdb_cache_t* cache, size_t capacity);
 
 /* Env */