text: -- 在WAL模式下, better-sqlite3可充分发挥性能
  PRAGMA journal_mode = WAL;
  
  CREATE TABLE cache_metadata (
    key                  TEXT    NOT NULL UNIQUE
  , updated_at           INTEGER NOT NULL
  , time_to_live         INTEGER NULL
  , time_before_deletion INTEGER NULL
  ) STRICT;
  
  CREATE INDEX idx_cache_metadata_deletion_time
            ON cache_metadata(updated_at + time_to_live + time_before_deletion)
         WHERE time_to_live IS NOT NULL
           AND time_before_deletion IS NOT NULL;
  