| From: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)2ndquadrant(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Noah Misch <noah(at)leadboat(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: pgsql: Fix a couple of bugs in MultiXactId freezing |
| Date: | 2013-12-03 18:40:44 |
| Message-ID: | 20131203184044.GF5158@eldon.alvh.no-ip.org |
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| Lists: | pgsql-committers pgsql-hackers |
Andres Freund wrote:
> I wondered about that myself. How would you suggest the format to look
> like?
> ISTM per tuple we'd need:
>
> * OffsetNumber off
> * uint16 infomask
> * TransactionId xmin
> * TransactionId xmax
>
> I don't see why we'd need infomask2, but so far being overly skimpy in
> that place hasn't shown itself to be the greatest idea?
I don't see that we need the xmin; a simple bit flag indicating whether
the Xmin was frozen should be enough.
For xmax we need more detail, as you propose. In infomask, are you
proposing to store the complete infomask, or just the flags being
changed? Note we have a set of bits used in other wal records,
XLHL_XMAX_IS_MULTI and friends, which perhaps we can use here.
--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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