Method ShardedCache

be/src/util/cache/cache-internal.h:243–262

class ShardedCache : public Cache {
 public:
  explicit ShardedCache(Cache::EvictionPolicy policy, size_t capacity, const string& id)
      : shard_bits_(DetermineShardBits()) {
    // A cache is often a singleton, so:
    // 1. We reuse its MemTracker if one already exists, and
    // 2. It is directly parented to the root MemTracker.
    // TODO: Change this to an Impala MemTracker, and only track the memory usage for the
    // metadata. This currently does not hook up to Impala's MemTracker hierarchy
    mem_tracker_ = kudu::MemTracker::FindOrCreateGlobalTracker(
        -1, strings::Substitute("$0-sharded_$1_cache", id, ToString(policy)));

    int num_shards = 1 << shard_bits_;
    const size_t per_shard = (capacity + (num_shards - 1)) / num_shards;
    for (int s = 0; s < num_shards; ++s) {
      shards_.push_back(NewCacheShard(policy, mem_tracker_.get(), per_shard));
    }

    if (per_shard < shard_charge_limit_) {
      shard_charge_limit_ = static_cast<int>(per_shard);
    }
  }

  virtual ~ShardedCache() {
    STLDeleteElements(&shards_);