Re: WIP: Avoid creation of the free space map for small tables

On 12/8/18, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> On Fri, Dec 7, 2018 at 7:25 PM John Naylor <jcnaylor(at)gmail(dot)com> wrote:
> I couldn't resist the temptation to figure out what's going on here.
> The newly added tests have deletes followed by vacuum and then you
> check whether the vacuum has removed the data by checking heap and or
> FSM size. Now, when you run such a test in parallel, the vacuum can
> sometimes skip removing the rows because there are parallel
> transactions open which can see the deleted rows.

Ah yes, of course.

> You can easily
> verify this phenomenon by running the newly added tests in one session
> in psql when there is another parallel session which has an open
> transaction. For example:
>
> Session-1
> Begin;
> Insert into foo values(1);
>
> Session-2
> \i fsm.sql
>
> Now, you should see the results similar to what you are seeing when
> you ran the fsm test by adding it to one of the parallel group. Can
> you test this at your end and confirm whether my analysis is correct
> or not.

Yes, I see the same behavior.

> So, you can keep the test as you have in parallel_schedule, but
> comment needs to be changed. Also, you need to add the new test in
> serial_schedule. I have done both the changes in the attached patch,
> kindly confirm if this looks correct to you.

Looks good to me. I'll just note that the new line in the serial
schedule has an extra space at the end. Thanks for looking into this.

-John Naylor