constexpr size_t kDefaultBlockSize = 64 * 1024 * 1024;
// The environment variable that overrides the max size of the LRU cache of
// blocks read from GCS. Specified in MB.
constexpr char kMaxCacheSize[] = "GCS_READ_CACHE_MAX_SIZE_MB";
constexpr size_t kDefaultMaxCacheSize = 0;
// The environment variable that overrides the maximum staleness of cached file