On 11.01.2021 01:35, Tomas Vondra wrote:
> Hi,
>
> I started looking at this patch again, hoping to get it committed in
> this CF, but I think there's a regression in handling TOAST tables
> (compared to the v3 patch submitted by Pavan in February 2019).
>
> The test I'm running a very simple test (see test.sql):
>
> 1) start a transaction
> 2) create a table with a text column
> 3) copy freeze data into it
> 4) use pg_visibility to see how many blocks are all_visible both in the
> main table and it's TOAST table
>
> For v3 patch (applied on top of 278584b526 and
> s/hi_options/ti_options) I get this:
>
> pages NOT all_visible
> ------------------------------------------
> main 637 0
> toast 50001 3
>
> There was some discussion about relcache invalidations causing a
> couple TOAST pages not be marked as all_visible, etc.
>
> However, for this patch on master I get this
>
> pages NOT all_visible
> ------------------------------------------
> main 637 0
> toast 50001 50001
>
> So no pages in TOAST are marked as all_visible. I haven't investigated
> what's causing this, but IMO that needs fixing to make ths patch RFC.
>
> Attached is the test script I'm using, and a v5 of the patch - rebased
> on current master, with some minor tweaks to comments etc.
>
Thank you for attaching the test script. I reproduced the problem. This
regression occurs because TOAST internally uses heap_insert().
You have asked upthread about adding this optimization to heap_insert().
I wrote a quick fix, see the attached patch 0002. The TOAST test passes
now, but I haven't tested performance or any other use-cases yet.
I'm going to test it properly in a couple of days and share results.
With this change a lot of new code is repeated in heap_insert() and
heap_multi_insert(). I think it's fine, because these functions already
have a lot in common.
--
Anastasia Lubennikova
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company
