On Thu, 7 Jul 2022 at 04:07, DAVID ROTH <adaptron@xxxxxxxxxxx> wrote: > I understand the planner can use multiple indexes to get the best plan. > Can someone point me a paper that explains how this works. I don't know of a paper, but if you're talking about using multiple indexes to scan a single relation in order to satisfy a condition such as; WHERE a = 5 OR b = 12; then the query planner is able to make use of "bitmap index scans". A bitmap index scan simply scans an index type which supports such scans and collects a set of ctids. For this example, providing there's a suitable index on the "a" column and another on the "b" column, the planner may choose to perform a bitmap index scan on the "a" index and another on the "b" index then perform a bitmap OR operation to obtain the intersecting ctids. The heap of the table can then be scanned to fetch the intersecting ctids. A ctid is the physical (more physiological) address of a tuple the heap of a table. David
