Re: BUG #19037: Planner fails on estimating array length with "no relation entry" error

Richard Guo <guofenglinux@gmail.com>

From: Richard Guo <guofenglinux@gmail.com>

To: Tom Lane <tgl@sss.pgh.pa.us>

Cc: exclusion@gmail.com, pgsql-bugs@lists.postgresql.org

Date: 2025-09-01T07:32:43Z

Lists: pgsql-bugs

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Fix planner error when estimating SubPlan cost
- 8c02d92c6475 13.23 landed
- 160ef51c8dba 14.20 landed
- 53e35fb560ab 15.15 landed
- 79ade5873232 16.11 landed
- f34202f51867 17.7 landed
- ab4a35b4ea9d 18.0 landed
- aba8f61c3091 19 (unreleased) landed

On Sun, Aug 31, 2025 at 6:51 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> The most expedient solution is probably to hack examine_variable
> so that it doesn't fail if root->simple_rel_array isn't there yet.
> That seems mighty ugly though.

As an alternative, I wonder if we could pass root as NULL to
cost_subplan() when it's called from build_subplan(), and possibly
also from SS_process_ctes().  At those points, the root does not yet
contain enough information to safely consult statistics.  Meanwhile,
cost_qual_eval() and the functions it calls are already well-equipped
to handle a NULL root.

- Richard