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

Hi

Whenever I'm debugging some kind of corruption incident, possible visibility bug, etc, I always land up staring at integer infomasks or using a SQL helper function to decode them.

That's silly, so here's a patch to teach pageinspect how to decode infomasks to a human readable array of flag names.

Example:

SELECT t_infomask, t_infomask2, flags

FROM heap_page_items(get_raw_page('test1', 0)),

     LATERAL heap_infomask_flags(t_infomask, t_infomask2, true) m(flags);

 t_infomask | t_infomask2 |                                   flags                                    

------------+-------------+----------------------------------------------------------------------------

       2816 |           2 | {HEAP_XMIN_COMMITTED,HEAP_XMIN_INVALID,HEAP_XMAX_INVALID,HEAP_XMIN_FROZEN}

(1 row)

To decode individual mask integers you can just call it directly. It's strict, so pass 0 for the other mask if you don't have both, e.g.

SELECT heap_infomask_flags(2816, 0);

The patch backports easily to older pageinspect versions for when you're debugging something old.

BTW, I used text[] not enums. That costs a fair bit of memory, but it doesn't seem worth worrying too much about in this context. 

For convenience it also tests and reports HEAP_LOCKED_UPGRADED and HEAP_XMAX_IS_LOCKED_ONLY as pseudo-flags.

I decided not to filter out HEAP_XMIN_COMMITTED,HEAP_XMIN_INVALID,HEAP_XMAX_INVALID when HEAP_XMIN_FROZEN is set