Subtransactions and performance degradation. Part 1: PGPROC_MAX_CACHED_SUBXIDS

Show how reaching higher numbers of subtransactions can affect performance. Questions:

• is reaching PGPROC_MAX_CACHED_SUBXIDS (default: 64) bad for performance?
• what sessions may be affected? (other sessions in the same logical DB; sessions to other logical DBs; sessions on replicas)

Related:

• https://gitlab.com/postgres/postgres/blob/def5b065ff22a16a80084587613599fe15627213/src/include/storage/proc.h#L36
• https://www.cybertec-postgresql.com/en/subtransactions-and-performance-in-postgresql/fbjetlbvjdgdjkkftfjllfn