Re: Reasons and drawbacks for unused item pointers (was: Update using primary key slow)

Tom Lane <tgl@sss.pgh.pa.us> writes:

> Denis <denis.sailer@yellowbook.com> writes:
>> There were 1905028 unused item pointers.
> The "unused item pointers" number seems a bit high, but otherwise that
> looks pretty reasonable.
>
> Is it possible that the particular row you were updating has been
> updated quite a lot of times since the last vacuum?  Or even quite
> a few times within a single transaction?

What causes this "unused item pointers" and which impact do they have
regarding performance?

If I understood your last posting correctly more than one update on a
single row between two vacuum's would i.e. result in one ore more
"unused item pointer". Does this slow down the vacuum process and/or
other processes?  Until now I could not find an answer what this number
implies.

Regards

Martin