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

From: Claudio Freire <klaussfreire(at)gmail(dot)com>
To: Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>
Cc: PostgreSQL-Dev <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [HACKERS] [PATCH] Vacuum: Update FSM more frequently
Date: 2018-03-02 13:47:54
Message-ID: CAGTBQpYDobSyhY=-+4_yhTM6s1Rg+0r5+22B4RcoUs+iY=eNDA@mail.gmail.com
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On Fri, Mar 2, 2018 at 7:38 AM, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)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.

Attachment Content-Type Size
0001-Vacuum-Update-FSM-more-frequently-v8.patch text/x-patch 14.9 KB

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