Re: BUG #16329: Valgrind detects an invalid read when building a gist index with buffering

On Wed, Mar 29, 2023 at 06:21:38PM -0400, Tom Lane wrote:
> *** a/src/test/regress/sql/gist.sql
> --- b/src/test/regress/sql/gist.sql
> *************** select p from gist_tbl order by circle(p
> *** 170,175 ****
> --- 170,180 ----
>   select p from gist_tbl order by circle(p,1) <-> point(0,0) limit 1;
>   
>   -- Force an index build using buffering.
> + insert into gist_tbl
> + select box(point(0.05*i, 0.05*i), point(0.05*i, 0.05*i)),
> +        point(0.05*i, 0.05*i),
> +        circle(point(0.05*i, 0.05*i), 1.0)
> + from generate_series(10001,30000) as i;
>   create index gist_tbl_box_index_forcing_buffering on gist_tbl using gist (p)
>     with (buffering=on, fillfactor=50);
>   
> The question is whether it's worth the extra test cycles forevermore.
> On my machine, the time for the gist test script goes from ~400ms to
> ~600ms.  That's still less than some of the concurrent scripts (brin,
> privileges, and join_hash all take more than that for me), so maybe
> it's fine.  But it seems like a lot for a change that doesn't move the
> raw code coverage results by even one line.

I say +200ms is fine.  This thread is a reminder of the limits of raw code
coverage as a measure of tests.  (I expect this will add tens of minutes to
the soft-float buildfarm animal runs, but they deserve it.)