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Paginated document assembly pattern

The Paginated document assembly pattern is a software design pattern used to generate large reports efficiently by processing data in chunks and combining file fragments.[001-todo-code.md:36-89][001-todo-code.md:130-219] This approach is commonly used in systems that handle heavy workloads, such as enterprise reporting or data export services, to optimize memory usage and execution time.

Key Characteristics

The pattern typically involves temporary storage and a final assembly stage. Instead of generating a massive document in memory, the system creates smaller files for each page or chunk of data and stores them in a temporary directory^[001-todo-code.md:130-150]. Once all chunks are successfully generated, a background process (often an asynchronous worker) retrieves these files and merges them into a single, cohesive document[001-todo-code.md:130-219][001-todo-code.md:441-462].

Implementation Workflow

The workflow generally follows these steps:

  1. Record Creation: A database record is created to track the report's status (e.g., RUNNING, SUCCESS, FAIL).^[001-todo-code.md:764-781]
  2. Chunked Generation: As data arrives—often via a Message Queue or event stream—the system generates document fragments for the current page and saves them to a temporary path[001-todo-code.md:130-219][001-todo-code.md:208-217].
  3. Aggregation Check: The system monitors the temporary directory. Once the number of generated files matches the expected total page count, the process moves to the next stage^[001-todo-code.md:196-202].
  4. Combination: A listener or worker receives a signal to assemble the final document. It downloads the temporary files, merges them into a single byte stream, and uploads the final file to permanent storage^[001-todo-code.md:441-462].
  5. Cleanup: Temporary files are deleted, and the database record is updated to SUCCESS with the final file path[001-todo-code.md:458-465][001-todo-code.md:829-840].
  • [[Asynchronous processing]]
  • [[Message queues]]
  • [[File storage patterns]]
  • [[Domain-driven design]]

Sources

^[001-todo-code.md]