Because OP said they didn't know anything about postgres and were speaking in generic terms, and the way they said "switching to int64" and recompiling all binaries just stroke me as "if you want a 64 bit system, you need to recompile it" (which is true). I'm surprised it's a compile time constant, as I just learned.

Reading their post history now they probably do know what they're talking about, though.

There's a reason for even database servers with 32-bit transaction IDs to be 64-bit processes - performance and memory. AFAIK until Firebird 3.0, Firebird also had 64-bit server builds with 32-bit transaction IDs - it would have broken many external tools had the old on-disk format been changed.