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Re: Nested transactions and tuple header info

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Alvaro Herrera <alvherre(at)dcc(dot)uchile(dot)cl>
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: 2004-06-02 03:59:14
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
Alvaro Herrera wrote:
> > Also, we will need a phantom xid for every xid1/xid2 pair.  You can't
> > just create one phantom xid per subtransaction because you must be able
> > to control independently commit/rollback rows based on the status of the
> > insert transaction.
> Oh, sure.  This could get huge pretty fast.
> We still need to think on the effects this could have on crash recovery
> though -- we'd have to write the phantom Xids to Xlog somehow
> (indicating which ones are committed and which are aborted).  And we
> still don't know what effect it would have on CPU cost for every
> visibility check.

As I understand, this overhead would only be needed for subtransactions.
I also don't think there will be a lot of them because it is only for
creation/expire in the same main transaction, and it is only needed for
unique creation/expire combinations, which should be pretty small.

  Bruce Momjian                        |
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