Re: 9.2.1 & index-only scans : abnormal heap fetches after VACUUM FULL

On Sat, Feb 15, 2014 at 07:08:40PM +0100, Andres Freund wrote:
> > Can you be more specific about the cluster.c idea?  I see
> > copy_heap_data() in cluster.c calling HeapTupleSatisfiesVacuum() with a
> > 'buf' just like the code I am working in.
> 
> Yes, it does. But in contrast to your patch it does so on the *origin*
> buffer. Which is in shared memory.
> The idea would be to modify rewrite_heap_tuple() to get a new parameter
> informing it it about the tuple's visibility. That'd allow you to avoid
> doing any additional visibility checks.
> 
> Unfortunately that would still not fix the problem that
> visibilitymap_set requires a real buffer to be passed in. If you're
> going that route, you'll need to make a bit more sweeping changes. You'd
> need to add new blockno parameter and a BufferIsValid() check to the
> right places in log_heap_visible(). Pretty ugly if you ask me...

Thank you for the thorough review.  Unless someone else can complete
this, I think it should be marked as returned with feedback.  I don't
think I am going to learn enough to complete this during the
commit-fest.

Since learning of the limitations in setting vmmap bits for index-only
scans in October, I have been unable to improve VACUUM/CLUSTER, and
unable to improve autovacuum --- a double failure.  I guess there is
always PG 9.5.

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
 + Everyone has their own god. +