All Your GUCs in a Row: min_parallel_index_scan_size and min_parallel_table_scan_size

A deep dive into two PostgreSQL planner GUCs, min_parallel_table_scan_size (default 8MB) and min_parallel_index_scan_size (default 512kB), explaining how they gate eligibility for parallel scans and also set the starting rung of the tripling ladder that determines how many workers the planner requests. Includes benchmarked tables showing how worker counts change across settings, how setting either to 0 (common in test suites) can backfire in production by handing excessive workers to small tables, how CREATE INDEX and VACUUM use these parameters differently than the planner, and new PostgreSQL 19 behavior for TID range scans and parallel autovacuum. Recommends leaving both at defaults and using parallel_setup_cost or max_parallel_workers_per_gather instead for tuning.

Source: https://postgr.es/p/9wW. 8 Sync News only summarizes and links out; content copyright belongs to the authors and original sources.