Re: pageinspect: Hash index support

On Tue, Aug 30, 2016 at 10:06 AM, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
wrote:

> Jesper Pedersen wrote:
> > Hi,
> >
> > Attached is a patch that adds support for hash indexes in pageinspect.
> >
> > The functionality (hash_metap, hash_page_stats and hash_page_items)
> follows
> > the B-tree functions.
>
> I suggest that pageinspect functions are more convenient to use via the
> get_raw_page interface, that is, instead of reading the buffer
> themselves, the buffer is handed over from elsewhere and they receive it
> as bytea. This enables other use cases such as grabbing a page from one
> server and examining it in another one.
>

I've never needed to do that, but it does sound like it might be useful.
But it is also annoying to have to do that when you want to examine a
current server. Could we use overloading, so that it can be used in either
way?

For hash_page_items, the 'data' is always a 32 bit integer, isn't it?
(unlike other pageinspect features, where the data could be any
user-defined data type). If so, I'd rather see it in plain hex (without
the spaces, without the trailing zeros)

+ /* page type (flags) */
+ if (opaque->hasho_flag & LH_UNUSED_PAGE)
+ stat->type = 'u';

This can never be true, because LH_UNUSED_PAGE is zero. You should make
this be the fall-through case, and have LH_META_PAGE be explicitly tested
for.

Cheers,

Jeff