Re: Unneccessary cmax in heap tuple ?

devik(at)cdi(dot)cz wrote:

> > > Why is there cmax in tuple ? cxxx is used to determine
> > > if tuple was inserted/deleted by current command or
> > > past command. Because one command can't both insert
> > > and delete the same tuple, only something like "cupd"
> > > might be needed and flag which tells you whether cupd
> > > is time of insert or delete. This saves 4byte from
> > > header ..
> >
> > If a tuple was inserted and updated in current transaction,
> > how could we judge if the tuple was valid for a given
> > ScanCommandId ?
> > However there could be other improvements.
>
> Ahh I did not know that there is need to test tuple for
> validity for some past cid. I thought that we only need
> to know whether tuple has been updated by current cid
> to ensure that it will not be scanned again in the same
> cid... Where am I wrong ?

For example,INSENSITIVE cursors(though not implemented) ?
INSENSITIVE cursors see changes made by neither other
backends nor the backend itself.

Regards.
Hiroshi Inoue