> > >> 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
