Re: pg_controldata gobbledygook

On Fri, Apr 26, 2013 at 2:08 AM, Andres Freund <andres(at)2ndquadrant(dot)com>wrote:

> On 2013-04-25 23:07:02 -0400, Peter Eisentraut wrote:
> > I'm not sure who is supposed to be able to read this sort of stuff:
> >
> > Latest checkpoint's NextXID: 0/7575
> > Latest checkpoint's NextOID: 49152
> > Latest checkpoint's NextMultiXactId: 7
> > Latest checkpoint's NextMultiOffset: 13
> > Latest checkpoint's oldestXID: 1265
> > Latest checkpoint's oldestXID's DB: 1
> > Latest checkpoint's oldestActiveXID: 0
> > Latest checkpoint's oldestMultiXid: 1
> > Latest checkpoint's oldestMulti's DB: 1
> >
> > Note that these symbols don't even correspond to the actual symbols used
> > in the source code in some cases.
> >
> > The comments in the pg_control.h header file use much more pleasant
> > terms, which when put to use would lead to output similar to this:
> >
> > Latest checkpoint's next free transaction ID: 0/7575
> > Latest checkpoint's next free OID: 49152
> > Latest checkpoint's next free MultiXactId: 7
> > Latest checkpoint's next free MultiXact offset: 13
> > Latest checkpoint's cluster-wide minimum datfrozenxid: 1265
> > Latest checkpoint's database with cluster-wide minimum datfrozenxid: 1
> > Latest checkpoint's oldest transaction ID still running: 0
> > Latest checkpoint's cluster-wide minimum datminmxid: 1
> > Latest checkpoint's database with cluster-wide minimum datminmxid: 1
> >
> > One could even rearrange the layout a little bit like this:
> >
> > Control data as of latest checkpoint:
> > next free transaction ID: 0/7575
> > next free OID: 49152
>
> I have to admit I don't see the point. None of those values is particularly
> interesting to anybody without implementation level knowledge and those
> will likely deal with them just fine. And I find the version with the
> shorter names far quicker to read.
>

I agree. For the ones I didn't know the meaning of, I still don't know the
meaning of them based on the long form, either. While a tutorial on what
these things mean might be useful, embedding the tutorial into the output
of pg_controldata probably isn't the right place.

Cheers,

Jeff