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?

Marc G. Fournier ICQ#7615664 IRC Nick: Scrappy
Systems Administrator @ hub.org
primary: scrappy(at)hub(dot)org secondary: scrappy(at){freebsd|postgresql}.org