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2609e91fcf
Commit 51ee6f3160d2e1515ed6197594bda67eb99dc2cc accidentally changed the behavior around inheritance hierarchies; before, we always considered parallel paths even for very small inheritance children, because otherwise an inheritance hierarchy with even one small child wouldn't be eligible for parallelism. That exception was inadverently removed; put it back. In passing, also adjust the degree-of-parallelism comptuation for index-only scans not to consider the number of heap pages fetched. Otherwise, we'll avoid parallel index-only scans on tables that are mostly all-visible, which isn't especially logical. Robert Haas and Amit Kapila, per a report from Ashutosh Sharma. Discussion: http://postgr.es/m/CAE9k0PmgSoOHRd60SHu09aRVTHRSs8s6pmyhJKWHxWw9C_x+XA@mail.gmail.com