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RE: AW: Plans for solving the VACUUM problem

From: "Mikheev, Vadim" <vmikheev(at)SECTORBASE(dot)COM>
To: "'Zeugswetter Andreas SB'" <ZeugswetterA(at)wien(dot)spardat(dot)at>
Cc: "'pgsql-hackers(at)postgresql(dot)org'" <pgsql-hackers(at)postgresql(dot)org>
Subject: RE: AW: Plans for solving the VACUUM problem
Date: 2001-05-29 17:39:59
Message-ID: 3705826352029646A3E91C53F7189E3201665C@sectorbase2.sectorbase.com (view raw or flat)
Thread:
Lists: pgsql-hackers
> > > So are whole pages stored in rollback segments or just
> > > the modified data?
> > 
> > This is implementation dependent. Storing whole pages is
> > much easy to do, but obviously it's better to store just
> > modified data.
> 
> I am not sure it is necessarily better. Seems to be a tradeoff here.
> pros of whole pages:
> 	a possible merge with physical log (for first
>           modification of a page after checkpoint
> 		there would be no overhead compared to current 
>           since it is already written now)

Using WAL as RS data storage is questionable.

> 	in a clever implementation a page already in the
>           "rollback segment" might satisfy the 
> 		modification of another row on that page, and 
>           thus would not need any additional io.

This would be possible only if there was no commit (same SCN)
between two modifications.

But, aren't we too deep on overwriting smgr (O-smgr) implementation?
It's doable. It has advantages in terms of IO active transactions
must do to follow MVCC. It has drawback in terms of required
disk space (and, oh yeh, it's not easy to implement -:)).
So, any other opinions about value of O-smgr?

Vadim

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