Re: [HACKERS] [PATCH] Vacuum: Update FSM more frequently

On Mon, Feb 26, 2018 at 11:31 AM, Claudio Freire <klaussfreire(at)gmail(dot)com> wrote:
>> ----
>> + /*
>> + * If there are no indexes then we should periodically
>> vacuum the FSM
>> + * on huge relations to make free space visible early.
>> + */
>> + if (nindexes == 0 &&
>> + (vacuumed_pages - vacuumed_pages_at_fsm_vac) >
>> vacuum_fsm_every_pages)
>> + {
>> + /* Vacuum the Free Space Map */
>> + FreeSpaceMapVacuum(onerel, max_freespace);
>> + vacuumed_pages_at_fsm_vac = vacuumed_pages;
>> + max_freespace = 0;
>> + }
>>
>> I think this code block should be executed before we check if the page
>> is whether new or empty and then do 'continue'. Otherwise we cannot
>> reach this code if the table has a lot of new or empty pages.
>
> In order for the counter (vacuumed_pages) to increase, there have to
> be plenty of opportunities for this code to run, and I specifically
> wanted to avoid vacuuming the FSM too often for those cases
> particularly (when Vacuum scans lots of pages but does no writes).

Wait, I see what you mean. Entirely empty pages.

Ok, I can move it.