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

>> 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.