Re: XLByte* usage

On 2012-12-17 23:45:51 +0530, Pavan Deolasee wrote:
> On Mon, Dec 17, 2012 at 11:26 PM, Pavan Deolasee
> <pavan(dot)deolasee(at)gmail(dot)com> wrote:
>
> >>
> >
> > I probably did not mean increasing that to beyond 64-bit. OTOH I
> > wondered if we would ever want to steal a few bits from the LSN field,
> > given the numbers you just put out. But it was more of a question than
> > objection.
> >
>
> BTW, now that XLogRecPtr is uint64, can't we change the pd_lsn field
> to use the same type ? At least the following comment in bufpage.h
> looks outdated or at the minimum needs some explanation as why LSN in
> the page header needs to split into two 32-bit values.
>
> 123 /* for historical reasons, the LSN is stored as two 32-bit values. */
> 124 typedef struct
> 125 {
> 126 uint32 xlogid; /* high bits */
> 127 uint32 xrecoff; /* low bits */
> 128 } PageXLogRecPtr;

pg_upgrade'ability. The individual bytes aren't necessarily laid out the
same with two such uint32s as with one uint64.

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services