Re: [PATCH] pageinspect function to decode infomasks

On Fri, Oct 13, 2017 at 4:36 PM, Peter Geoghegan <pg@bowt.ie> wrote:
> No, I'm arguing that they're just bits. Show the bits, rather than
> interpreting what is displayed. Document that there are other logical
> states that are represented as composites of contradictory/mutually
> exclusive states.

/me shrugs.

I think it's perfectly sensible to view those 2 bits as making up a
2-bit field with 4 states rather than displaying each bit
individually, but you obviously disagree.  Fair enough.

>> I guess it ends wherever we decide to stop.
>
> You can take what you're saying much further. What about
> HEAP_XMAX_SHR_LOCK, and HEAP_MOVED? Code like HEAP_LOCKED_UPGRADED()
> pretty strongly undermines the idea that these composite values are
> abstractions.

HEAP_MOVED is obviously a different kind of thing.  The combination of
both bits has no meaning distinct from the meaning of the individual
bits; in fact, I think it's a shouldn't-happen state.  Not sure about
HEAP_XMAX_SHR_LOCK.

> pg_filedump doesn't display HEAP_XMIN_FROZEN, either. (Nor does it
> ever display any of the other composite t_infomask/t_infomask2
> values.)

I can think of two possible explanations for that.  Number one, the
tool was written before HEAP_XMIN_FROZEN was invented and hasn't been
updated for those changes.  Number two, the author of the tool agrees
with your position rather than mine.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company