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Re: Nested transactions and tuple header info

From: Alvaro Herrera <alvherre(at)dcc(dot)uchile(dot)cl>
To: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Manfred Koizar <mkoi-pg(at)aon(dot)at>,David Blasby <dblasby(at)refractions(dot)net>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Nested transactions and tuple header info
Date: 2004-06-03 20:21:06
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Lists: pgsql-hackers
On Wed, Jun 02, 2004 at 10:57:05AM -0400, Bruce Momjian wrote:
> Tom Lane wrote:
> > No, I said own xid --- so the "phantom xid" part is still there.  But
> > your idea definitely does *not* work unless you use a single CID
> > sequence for the whole main xact; and I'm still wondering if there's
> > not a simpler implementation possible given that assumption.
> I don't understand why a single counter is needed for phantom xids.  We
> keep the cmin/cmax on the tuple already, and our own backend can look up
> the xmin/xmax that goes with the phantom.

Not sure either way (maybe you are right), but I use the global counter
anyway because some tests would become a very ugly mess if I didn't.  I
think the phantom idea is also simpler with the global counter.

And I see no reason to use local counter.  We certainly are not
hitting the limit with the global counter, as Tom pointed out recently
in a thread about the aborted CID bitmaps.

Alvaro Herrera (<alvherre[a]>)
"Crear es tan difĂ­cil como ser libre" (Elsa Triolet)

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