> On 17 Sep 2025, at 14:51, David Rowley <[email protected]> wrote:
>
> What you'd need for this to ever be slow is lots of rescans, so
> something like TID Scan on the inside of a nested loop. If you look at
> ExecReScanTidScan() you'll see it pfrees the tss_TidList, which
> requires that the list gets built all over again on the next call to
> TidNext(). It's the call to TidListEval() that is potentially
> expensive due to the expression evaluation, memory allocation, sorting
> and distinct work.
Occasionally (when dealing with corruption) I do stuff like
begin;
update public.tablename set description = description where ctid in (select
('('||b.blkno::text||','||(x::text)||')')::tid from generate_series(1,300) x,
blocks b);
in some forms they are actually joins. Also, pageinspecting things out is
always a join (CTAS a copy of table rows that have particular infomask bits).
But, fortunately, it's not that frequent case. It's always "plumbing", not a
"regular database usage".
Best regards, Andrey Borodin.
