Plan operator
Gather
Plan node that collects rows from parallel worker processes back into the leader for the final result.
A Gather node is the parent of a parallel-aware subplan. Each worker process executes its slice of the plan independently, and Gather reads their output streams and forwards them to the rest of the query.
Its sibling Gather Merge keeps the result sorted: if every worker emits rows in the same order, Gather Merge performs a merge instead of an arbitrary interleave, preserving order for an upstream Limit or Sort-aware operator.
Parallel plans depend on max_parallel_workers_per_gather, table size relative to min_parallel_table_scan_size, and whether the operations involved are parallel-safe. If parallelism is unexpectedly absent, check those settings and the function volatility of any expressions in the query.