Issues with blocksize smaller than 8KB

I have been comparing performance of postgresql (18.0) compiled for various block sizes etc., and found that while 8kb
and16kb builds work fine, a 4kb build does not, with identical configuration.  When I try to initialize pgbench,
--scale=10works fine, but the --scale=100 I was trying and even just --scale=20 result in a long delay on the vacuum
analyzestep followed by Postgres crashing due to a segmentation fault. 

I also found that initdb fails when I compile for a blocksize of either 1KB or 2KB build:

2025-10-17 15:39:13.182 UTC [97433] DETAIL:  The database cluster was initialized with RELSEG_SIZE 1895825408, but the
serverwas compiled with RELSEG_SIZE 1895825408. 
2025-10-17 15:39:13.182 UTC [97433] HINT:  It looks like you need to recompile or initdb.

- Casey