Re: [HACKERS] [PATCH] pageinspect function to decode infomasks

On Tue, Aug 15, 2017 at 9:59 AM, Tomas Vondra
<tomas.vondra@2ndquadrant.com> wrote:
>> I don't think so -- the "committed" and "invalid" meanings are
>> effectively canceled when the "frozen" mask is present.
>>
>> I mean, "committed" and "invalid" contradict each other...
>
> FWIW I agree with Craig - the functions should output the masks raw, without
> any filtering. The reason is that when you're investigating data corruption
> or unexpected behavior, all this is very useful when reasoning about what
> might (not) have happened.
>
> Or at least make the filtering optional.

I don't think "filtering" is the right way to think about it.  It's
just labeling each combination of bits with the meaning appropriate to
that combination of bits.

I mean, if you were displaying the contents of a CLOG entry, would you
want the value 3 to be displayed as COMMITTED ABORTED SUBCOMMITTED
because TRANSACTION_STATUS_COMMITTED|TRANSACTION_STATUS_ABORTED ==
TRANSACTION_STATUS_SUB_COMMITTED?

I realize that you may be used to thinking of the HEAP_XMIN_COMMITTED
and HEAP_XMAX_COMMITTED bits as two separate bits, but that's not
really true any more.  They're a 2-bit field that can have one of four
values: committed, aborted, frozen, or none of the above.

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