Re: Vacuum full: alternatives?

On 6/20/2016 8:51 AM, David G. Johnston wrote:
>
>
> incorrect. in fact, an update is performed identically to an
> INSERT + DELETE(old)
>
>
> Except for heap-only-tuple optimization, right? We cannot build a HOT
> chain if the user requests a delete separately since their is no
> longer an association to trace from the old record.
>
> I suspect this affects free space usage to some degree as well but I
> agree and believe that the reclaimed space is not forbidden to be used
> (I wouldn't rely on my word though and haven't tried to find relevant
> documentation).

yeah, HOT only works on updates that don't modify any indexed fields,
and only if there's adequate free space in the same block. If you have
a update intensive table thats a candidate for HOT, I've been
recommending setting that table's fill factor to 50-70% prior to
populating it to leave freespace in every block.

--
john r pierce, recycling bits in santa cruz