From: | Jinhua Luo <luajit(dot)io(at)gmail(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: insert/update performance |
Date: | 2016-01-27 06:04:33 |
Message-ID: | CAAc9rOywTRm4CSAGST8w5q5xqou2HX7E+r1AL8poBPprb1PL3Q@mail.gmail.com |
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Lists: | pgsql-hackers |
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
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