To know how much RAM a connection may use, we start with a baseline of eight megabytes. This accounts for library overhead, likelihood of using temporary table space, and other various allocations necessary for a session to function. To that, we add four times the work_mem setting used by the server to sort and perform query calculations.
Why four? Large and complex queries will use more, while short and simple queries will use less, so we start with something in the middle. It's actually possible that this multiplier is somewhat pessimistic, so it trends toward assuming higher memory use. That's fine, since overestimating in this case is safer than running out of memory in the presence of several simultaneous complex queries. ...
