Re: fillfactor and cluster table vs ZFS copy-on-write

On Fri, Apr 17, 2015 at 5:24 AM, Albe Laurenz <laurenz(dot)albe(at)wien(dot)gv(dot)at>
wrote:

> >> Even with COW, I can see fillfactor < 100% still have its virtues. For
> >> example, HOT update can avoid adding an extra index item on the index
> >> page if it finds the new item can be inserted in the same heap page.
>
> > That's true, the new physical location on disk is transparent to the
> DBMS so it has no more or less
> > housekeeping with or without COW, but the housekeeping still has to be
> done somewhere, so it helps to
> > understand which is more efficient. I'll see if I can produce some
> empirical data unless anyone thinks
> > it's a waste of time.
>
> I am quite certain that fillfactor < 100% will be a win even then (for the
> right load).
> Upating one (heap) block should always be cheaper than updating one heap
> block
> as well as (at least) one index block per index involved.

Your last three words. I was ignoring the obvious (and likely) scenario of
when more than one index needs to be updated.

fillfactor<100% with COW still gets the win.

Thanks!

Geoff