All Your GUCs in a Row: max_parallel_workers and max_parallel_workers_per_gather

An in-depth breakdown of two frequently misunderstood PostgreSQL configuration parameters, max_parallel_workers_per_gather and max_parallel_workers. It explains that the former caps workers per Gather/Gather Merge plan node (not a global limit) while the latter is a cluster-wide count checked against each session's own private setting, which can lead to surprising starvation of logical replication workers or other parallel plans if misconfigured. It covers defaults, history since PostgreSQL 9.6/10, how the planner actually computes worker counts based on table size, the parallel_workers storage parameter and enable_parallel_append exceptions, new PostgreSQL 18 stats columns (parallel_workers_to_launch/launched), and concrete tuning guidance for max_worker_processes, max_parallel_workers, and max_parallel_workers_per_gather.

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