Re: [HACKERS] [WIP] Zipfian distribution in pgbench

On Thu, Jul 13, 2017 at 12:49 PM, Peter Geoghegan <pg@bowt.ie> wrote:
> To reiterate what I say above:
>
> The number of leaf pages with dead items is 20 with this most recent
> run (128 clients, patched + unpatched). The leftmost internal page one
> level up from the leaf level contains 289 items. Whereas last time it
> was 353 items.
>
> That's a difference between having 20 hot/bloated leaf pages, and
> probably 84 hot/bloated pages, which I infer must have been the total
> number of bloated leaf pages within "result.txt". I think that
> something about all the "pgbench_index_*txt" tests are very different
> to what we see within "result.txt". It's as if there was a problem
> when "result.txt" ran, but that problem somehow didn't come up when
> you did new tests.

I just figured out that "result.txt" is only a 60 second pgbench run.
Is the same true for other tests?

It would be much more interesting to see runs that lasted 10 minutes
or more. Maybe with pgbench-tools. I would expect that a decline in
performance due to bloating the index could happen only after a
certain threshold was crossed. Things like HOT pruning and LP_DEAD
cleanup could be pretty effective, until finally a tipping point is
reached and they're much less effective.

-- 
Peter Geoghegan