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

On Fri, Mar 2, 2018 at 7:38 AM, Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> Thank you for updating the patches!
>
> +/*
> + * When a table has no indexes, vacuum the FSM at most every this
> + * many dirty pages. With a default page size of 8kb, this value
> + * basically means 8GB of dirtied pages.
> + */
> +#define VACUUM_FSM_EVERY_PAGES 1048576
>
> Is it better if we vacuum fsm every 8GB regardless of the block size?
> Because an installation that uses >8GB block size is likely to have
> the pages less than what an 8GB block size installation has, the
> current patch might lead to delay fsm vacuum. What do you think? If
> it's better, we can define it as follows.
>
> #define VACUUM_FSM_EVERY_PAGES ((8 * 1024 * 1024) / BLCKSZ)

I honestly don't know. I've never tweaked page size, and know nobody
that did, so I have no experience with those installations.

Lets go with your proposal.

>
> --
> @@ -470,7 +484,9 @@ lazy_scan_heap(Relation onerel, int options,
> LVRelStats *vacrelstats,
>      TransactionId relfrozenxid = onerel->rd_rel->relfrozenxid;
>      TransactionId relminmxid = onerel->rd_rel->relminmxid;
>      BlockNumber empty_pages,
> -                vacuumed_pages;
> +                vacuumed_pages,
> +                fsm_updated_pages,
> +                vacuum_fsm_every_pages;
>      double        num_tuples,
>                  tups_vacuumed,
>                  nkeep,
>
> Regarding fsm_updated_pages variable name, I think it's better to be
> freespace_updated_pages because we actually counts the page updated
> its freespace, not fsm.

Good point.

New version attached.