Per the following link: https://www.sobyte.net/post/2022-08/postgres-snapshot/
To get a snapshot we need to know xmin, xmax and xip. my question is why do we need them? Since every tuple in a page has t_xmin and t_xmax based on the page layout(https://www.postgresql.org/docs/current/storage-page-layout.html), if we has a snapshot at xip 12345, couldn't we just check every tuple whose t_xmin is lower than 12345 and already committed?
Thanks,
Qihua
