| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
| Cc: | Alvaro Herrera <alvherre(at)dcc(dot)uchile(dot)cl>, 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 03:44:13 |
| Message-ID: | 19674.1086147853@sss.pgh.pa.us |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers |
Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> Tom Lane wrote:
>> You can't change xmin --- this would break visibility tests.
> Basically the phantom xid's are a shorthand for saying the tuple was
> created by xid1 and deleted by xid2, both part of the same main
> transaction.
That would be fine if the shorthand were readable, but it's not.
> A cursor looking at the rows has to recognize the xid is a phantom (via
> pg_subtrans) and look up the creation xid.
And it will find that how? Imagine that the creating transaction is
itself a subtransaction, and the deleting one is a few nesting levels
further down. I don't see how the tuple is going to carry enough
information to let you determine what's what, if the deleting subxact
overwrites the creating one's XID.
regards, tom lane
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Bruce Momjian | 2004-06-02 03:50:13 | Re: Nested transactions and tuple header info |
| Previous Message | Tom Lane | 2004-06-02 03:39:57 | Re: Why repalloc() != realloc() ? |