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Re: Unneccessary cmax in heap tuple ?

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: devik(at)cdi(dot)cz
Cc: Hiroshi Inoue <Inoue(at)tpf(dot)co(dot)jp>, pgsql-hackers(at)postgreSQL(dot)org
Subject: Re: Unneccessary cmax in heap tuple ?
Date: 2000-10-25 18:04:38
Message-ID: 29100.972497078@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
devik(at)cdi(dot)cz writes:
> 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 ?

In situations like SQL function calls, it may be necessary to suspend
a table scan while we go off and do other commands, then come back and
resume the table scan.  So there can be multiple scans with different
command IDs in progress within a transaction.

			regards, tom lane

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