Re: I: About "Our CLUSTER implementation is pessimal" patch

On Mon, Oct 4, 2010 at 4:47 PM, Leonardo Francalanci <m_lists(at)yahoo(dot)it> wrote:
>> It sounds like the costing model might need a bit more work before  we commit
>>this.
>
>
> I tried again the simple sql tests I posted a while ago, and I still get the
> same ratios.
> I've tested the applied patch on a dual opteron + disk array Solaris machine.
>
> I really don't get how a laptop hard drive can be faster at reading data using
> random
> seeks (required by the original cluster method) than seq scan + sort for the 5M
> rows
> test case.
> Same thing for the "cluster vs bloat" test: the seq scan + sort is faster on my
> machine.

Well, my last tests showed that the planner was choosing an index scan
for queries like:

SELECT * FROM atable ORDER BY akey;

but forcing a seqscan + sort made this faster, as you expect. So I was
thinking my cost settings (posted upthread) probably need some
tweaking, unless it's a problem with the optimizer. But all of this is
unrelated to the patch.

[... pokes a bit more ...] Sigh, now I'm finding it impossible to
reproduce my own results, particulary the earlier cluster_vs_bloat.sql
test of:

* 10M rows: 84 seconds for seq. scan, 44 seconds for index scan

I'm getting about 5 seconds now for the cluster, both with and without
the patch. effective_cache_size doesn't seem to impact this much. I'll
have another look when I have some more time.

Josh