Re: [HACKERS] row reuse while UPDATE and vacuum analyze problem

> On Wed, 28 Jul 1999, Oleg Bartunov wrote:
> 
> > How update performance could be increased if:
> >  1. 'vacuum analyze' will analyze index file
> >  2. reuse row instead of inserting
> 
> Just to clarify, 'reuse row' won't replace inserting (to the best of my
> knowledge), only reduce space wastage between vacuum's.  Especially, again
> TTBOMK, with MVCC, where each "instance" of a row is serialized.  
> 
> Actually, there is a tought...if I understand the concept of MVCC, how is
> reusing a row going to work?  My understanding is that I can "physically"
> have to copies of a row in a table, one newer then the other.  So, if
> someone is running a SELECT while I'm doing an UPDATE, their SELECT will
> take the older version of hte row (the row at the time their SELECT
> started)...depending on how busy that table is, there will have to be some
> sort of mechanism for determining how 'stale' a row is, no?
> 
> ie. on a *very* large table, with multiple SELECT/UPDATEs happening?

You would have to leave referenced rows alone.  I think Vadim has this
covered.

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