For application time, everything lives in one table (although you could partition it). The biggest performance hit, I suspect, will come from GiST indexes instead of B-Trees. Some general GiST improvements are on my TODO list, and I learned at PGConf.dev that several other people already have patches for cool perf-related GiST enhancements.

For system time, a separate history table is a common implementation, sometimes also with partitioning. Here is what other vendors are doing: https://illuminatedcomputing.com/posts/2019/08/sql2011-surve...