Method Lookup

be/src/runtime/io/data-cache.cc:834–875

}

int64_t DataCache::Partition::Lookup(const CacheKey& cache_key, int64_t bytes_to_read,
    uint8_t* buffer) {
  DCHECK(!closed_);
  DCHECK(trace_replay_ ? buffer == nullptr : buffer != nullptr);
  Slice key = cache_key.ToSlice();
  Cache::UniqueHandle handle(meta_cache_->Lookup(key));

  if (handle.get() == nullptr) {
    Trace(trace::EventType::MISS, cache_key, bytes_to_read, /*entry_len=*/-1);
    return 0;
  }

  // Read from the backing file.
  CacheEntry entry(meta_cache_->Value(handle));

  Trace(trace::EventType::HIT, cache_key, bytes_to_read, entry.len());

  bytes_to_read = min(entry.len(), bytes_to_read);
  // Skip the actual reads if doing trace replay
  if (LIKELY(!trace_replay_)) {
    CacheFile* cache_file = entry.file();
    VLOG(3) << Substitute("Reading file $0 offset $1 len $2 checksum $3 bytes_to_read $4",
        cache_file->path(), entry.offset(), entry.len(), entry.checksum(), bytes_to_read);
    bool read_success;
    {
      ScopedHistogramTimer read_timer(read_latency_);
      read_success = cache_file->Read(entry.offset(), buffer, bytes_to_read);
    }
    if (UNLIKELY(!read_success)) {
      meta_cache_->Erase(key);
      return 0;
    }

    // Verify checksum if enabled. Delete entry on checksum mismatch.
    if (FLAGS_data_cache_checksum && bytes_to_read == entry.len() &&
        !VerifyChecksum("read", entry, buffer, bytes_to_read)) {
      meta_cache_->Erase(key);
      return 0;
    }
  }
  return bytes_to_read;
}

bool DataCache::Partition::HandleExistingEntry(const Slice& key,
    const Cache::UniqueHandle& handle, const uint8_t* buffer, int64_t buffer_len) {