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 and 16kb builds work fine, a 4kb build does not, with identical configuration. When I try to initialize pgbench, --scale=10 works fine, but the --scale=100 I was trying and even just --scale=20 result in a long delay on the vacuum analyze step 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 server was 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