Re: [HACKERS] vacuum process size

Then <tgl(at)sss(dot)pgh(dot)pa(dot)us> spoke up and said:
> So doubling the array size at each step is a good change.
>
> But there are a lot more tuples than pages in most relations.
>
> I see two lists with per-tuple data in vacuum.c, "vtlinks" in
> vc_scanheap and "vtmove" in vc_rpfheap, that are both being grown with
> essentially the same technique of repalloc() after every N entries.
> I'm not entirely clear on how many tuples get put into each of these
> lists, but it sure seems like in ordinary circumstances they'd be much
> bigger space hogs than any of the three VPageList lists.
>
> I recommend going to a doubling approach for each of these lists as
> well as for VPageList.

Question: is there reliable information in pg_statistics (or other
system tables) which can be used to make a reasonable estimate for the
sizes of these structures before initial allocation? Certainly the
file size can be gotten from a stat (some portability issues, sparse
file issues).

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