Re: TOAST usage setting

Gregory Stark wrote:
> "Gregory Stark" <stark(at)enterprisedb(dot)com> writes:
>
> > "Bruce Momjian" <bruce(at)momjian(dot)us> writes:
> >
> >> shared_buffers again was 32MB so all the data was in memory.
> >
> > The case where all the data is in memory is simply not interesting. The cost
> > of TOAST is the random access seeks it causes. You seem to be intentionally
> > avoiding testing the precise thing we're interested in.
>
> Also, something's not right with these results. 100,000 tuples --even if all
> they contain is a toast pointer-- won't fit on a single page. And the toast
> tables should vary in size depending on how many toast chunks are created.

The test creates _one_ row of length 100,000 and then finds out how long
it takes to access it twenty times.

I don't see how having the data outside cache helps us. For a large row
with 2k chunks, I assume all the 2k chunks are going to be in the same
8k page. What I want to measure is the cost of accessing four 2k chunks
vs. one 8k chunk, and I think we can conclude that is 6% of the access
time.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://www.enterprisedb.com

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