Method PersistentCacheGarbageCollect

src/tabletnode/tabletnode_impl.cc:1422–1481

}

void TabletNodeImpl::PersistentCacheGarbageCollect(const std::set<std::string>& inherited_files,
                                                   const std::set<std::string>& active_tablets) {
  std::shared_ptr<leveldb::PersistentCache> p_cache;
  if (!io::GetPersistentCache(&p_cache).ok() || !p_cache) {
    return;
  }
  leveldb::StopWatchMicro timer(leveldb::Env::Default(), true);
  std::vector<std::string> all_keys{p_cache->GetAllKeys()};
  /*
   * all cached tablets/files:
   * ------------------------------------------
   * | active tablets  |   inactive tablets   |
   * |                 |                      |
   * |                 |    all    |    to    |
   * |                 | inherited | *DELETE* |
   * |                 |    files  |          |
   * ------------------------------------------
   * We need to save active tablets' files and inherited files.
   * Try remove files of tablets not on this tabletserver.
   * Here is the gc rule:
   *
   * Key format in persistent cache:  |table_name/tablet_name/lg_num/xxxxxxxx.sst|
   *                                  |          1           |                   |
   * string in active_tablets         |table_name/tablet_name|                   |
   *                                  |                      2                   |
   * string in inherited_files        |table_name/tablet_name/lg_num/xxxxxxxx.sst|
   *
   * If part 1 of persistent cache key doesn't match any string in active tablets,
   * and part 2 of it doesn't match any one in inherited_files, we'll remove it.
   */
  std::unordered_set<std::string> new_delayed_gc_files;
  for (auto& key : all_keys) {
    if (inherited_files.find(key) != inherited_files.end()) {
      // 1. If file name in inherited_files, skip it.
      continue;
    }
    std::vector<std::string> splited_terms;
    SplitString(key, "/", &splited_terms);
    assert(splited_terms.size() > 2);
    // 2. Extract table_name/tablet_name from persistent key.
    std::string tablet_name = splited_terms[0] + "/" + splited_terms[1];
    if (active_tablets.find(tablet_name) != active_tablets.end()) {
      // 3. Skip active tablets' file.
      continue;
    }
    if (delayed_gc_files_.find(key) != delayed_gc_files_.end()) {
      LOG(INFO) << "[Persistent Cache GC] Remove unused file: " << key << ".";
      // 4. If this key has already be delayed for one gc period, remove it.
      p_cache->ForceEvict(key);
    } else {
      LOG(INFO) << "[Persistent Cache GC] Add file: " << key << " to delayed gc files.";
      // 5. Otherwise, it'll be add to delayed_gc_files, waiting for next gc process.
      new_delayed_gc_files.emplace(key);
    }
  }

  std::swap(delayed_gc_files_, new_delayed_gc_files);
  p_cache->GarbageCollect();