Ok, I found the vaccum output is correct.
I check the codes of lazy_scan_heap(), the rows to be removed are
reported in two parts, one is return of heap_page_prune(), the other
is ItemIdIsDead() when scanning the page.
After scanning all pages of the relation, those rows would be clean up in:
if (vacrelstats->num_dead_tuples > 0) {
...
lazy_vacuum_heap()
...
}
It would then output
> INFO: "test": removed 6 row versions in 1 pages
The number of rows is correct.
But what kind of rows would satisfy heap_page_prune() and what would not?
In my case all updates are doing the same thing (there is no HOT
updates, obviously), but why some updated rows are reported by
heap_page_prune() but the others are not? And it's also a random
issue. That means sometimes heap_page_prune() would report all
removable rows, and sometimes it reports no rows.
Regards,
Jinhua Luo
