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Re: Unneccessary cmax in heap tuple ?

From: devik(at)cdi(dot)cz
To: Hiroshi Inoue <Inoue(at)tpf(dot)co(dot)jp>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Unneccessary cmax in heap tuple ?
Date: 2000-10-25 12:06:12
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
> > 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 ?

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