A reporting query computed hundreds of boolean expressions per row (many correlated EXISTS subqueries over a history table) inside `count(*) filter (where ...)` aggregates. Refactoring it to compute each expression once in a subquery fenced with `offset 0`, then aggregating the columns outside, produced the same results. Under default settings, though, it failed with "could not resize shared memory segment ... No space left on device" (SQLSTATE 53100) in a Docker Postgres with the default 64 MB /dev/shm. It was also not reliably faster. A `cross join lateral (select ... offset 0)` variant avoided the error but ran about 15% slower.