
> > >> Impractical ? Oracle does it.
> > >
> > >Oracle has MVCC?
> > 
> > With restrictions, yes.
> 
> What restrictions? Rollback segments size?

No, that is not the whole story. The problem with their "rollback segment approach" is,
that they do not guard against overwriting a tuple version in the rollback segment. 
They simply recycle each segment in a wrap around manner.
Thus there could be an open transaction that still wanted to see a tuple version
that was already overwritten, leading to the feared "snapshot too old" error.

Copying their "rollback segment" approach is imho the last thing we want to do.

> Non-overwriting smgr can eat all disk space...
> 
> > You didn't know that?  Vadim did ...
> 
> Didn't I mention a few times that I was inspired by Oracle? -:)

Looking at what they supply in the feature area is imho good.
Copying their technical architecture is not so good in general.

Andreas

Fri, 25 May 2001 09:44:14 +0200
Zeugswetter Andreas SB  <ZeugswetterA@wien.spardat.at>
AW: Plans for solving the VACUUM problem 