On Fri, 16 Oct 2026 at 05:20, zengxx <[email protected]> wrote: > return DEFAULT_NUM_DISTINCT. A union containing millions of keys > therefore looks like a 200-distinct-value domain. That can make a > semi-join estimate that nearly every outer row matches, undercount > GROUP BY/DISTINCT output groups, or overstate Memoize hit rates.
If that's true for Memoize, please provide a test case that shows a Memoize node being used on a DEFAULT_NUM_DISTINCT estimate. There's specific coding in cost_memoize_rescan() which is meant to stop that from happening. David
