28 NOV 2025
David debugged: Investigated why prefetch ran serially rather than in parallel
David pushed for a deeper investigation after suspecting prefetch was fetching items sequentially, and discovered the pipeline was not parallelising fetches across items.
After seeing timestamps suggesting sequential prefetch, David asked for hard evidence.
four items appear to be fetched serially. 22:40:56, 22:42:28, 22:42:50, 22:43:18 — those spacings look sequential, not parallel. A single slow item stalls the rest. Parallelizing within extension relay concurrency limits could cut wall-clock to max(item) rather than sum(items). go actually investigate on production whether prefetch fetches serially instead of parallel. why????
The investigation confirmed the serial execution. David then approved a parallelisation plan with PREFETCH_ITEM_CONCURRENCY set to 6, dispatcher lanes increased from 8 to 12, and explicit rejection of any approach that required an extension upgrade.