Re: Reduce heap tuple header size

Jan, any update on this? Are the numbers correct?

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Jan Wieck wrote:
> Bruce Momjian wrote:
> >
> > Jan Wieck wrote:
> > >
> > > Did someone run at least pgbench with/without that patch applied?
> >
> > No, but he did perform this analysis:
> >
> > > thus reducing the additional cost to one t_infomask compare,
> > > because the Satisfies functions only access Cmin and Cmax,
> > > when HEAP_MOVED is known to be not set.
> > >
> > > OTOH experimenting with a moderatly sized "out of production"
> > > database I got the following results:
> > > | pages | pages |
> > > relkind | count | tuples | before| after | savings
> > > --------+-------+--------+-------+-------+--------
> > > i | 31 | 808146 | 8330 | 8330 | 0.00%
> > > r | 32 | 612968 | 13572 | 13184 | 2.86%
> > > all | 63 | | 21902 | 21514 | 1.77%
> > >
> > > 2.86% fewer heap pages mean 2.86% less disk IO caused by heap pages.
> > > Considering that index pages tend to benefit more from caching
> > > we conclude that heap pages contribute more to the overall
> > > IO load, so the total savings in the number of disk IOs should
> > > be better than the 1.77% shown in the table above. I think
> > > this outweighs a few CPU cycles now and then.
>
> This anawhat? This is a proof that this patch is able to save not even
> 3% of disk space in a production environment plus an assumption that the
> saved IO outweights the extra effort in the tuple visibility checks.
>
> Here are some numbers:
>
> P3 850MHz 256MB RAM IDE
> postmaster -N256 -B8192
> pgbench -i -s 10 db
> pgbench -c 20 -t 500 db
>
>
> Current CVS tip: tps 34.1, 38.7, 36.6
> avg(tps) 36.4
>
> With patch: tps 37.0, 41.1, 41.1
> avg(tps) 39.7
>
> So it saves less than 3% disk space at the cost of about 9% performance
> loss. If we can do the same the other way around I'd go for wasting some
> more disk space.
>
>
> Jan
>
> --
>
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