Why does moving the GeoTIFF writer before the Excel writer improve performance?

• A. Writers should be in alphabetical order by format name for best performance.
• B. It's always faster to write small datasets before large ones.
• C. GeoTIFF writers are always faster than Excel writers.
• D. Large GeoTIFF files were previously being cached while waiting for the Excel file to be written.

Answer: (D)

When you reorder writers in an FME workflow, you’re changing when heavy I/O tasks start and how data sits in memory and on disk. Writing a large GeoTIFF is a big I/O operation, so it tends to generate a lot of data that could get buffered in memory or disk cache while another, slower writer (like Excel) is still processing. If the GeoTIFF writer runs after the Excel writer, that large amount of data may stay cached and waiting, tying up resources and slowing the overall flow.

Placing the GeoTIFF writer first starts that heavy write earlier, so the large data can be flushed out and the I/O work can proceed in parallel with the Excel writing. Once the GeoTIFF writing has progressed or finished, the Excel writer continues, with less caching pressure and less contention. The result is better overall throughput because the system isn’t holding a big GeoTIFF cache while waiting on the Excel write.

This isn’t about format speed, alphabetical order, or dataset size alone; it’s about how I/O work and caching interact in the pipeline.