Re: pgsql: Add contrib/pg_walinspect.

On Wed, Apr 27, 2022 at 8:45 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> I wrote:
> > Thomas Munro <thomas(dot)munro(at)gmail(dot)com> writes:
> >> BTW If you had your local change from debug.patch (upthread), that'd
> >> defeat the patch. I mean this:
>
> >> + if(!*errormsg)
> >> + *errormsg = "decode_queue_head is null";
>
> > Oh! Okay, I'll retry without that.
>
> I've now done several runs with your patch and not seen the test failure.
> However, I think we ought to rethink this API a bit rather than just
> apply the patch as-is. Even if it were documented, relying on
> errormsg = NULL to mean something doesn't seem like a great plan.

Sorry for being late in the game, occupied with other stuff.

How about using private_data of XLogReaderState for
read_local_xlog_page_no_wait, something like this?

typedef struct ReadLocalXLogPageNoWaitPrivate
{
bool end_of_wal;
} ReadLocalXLogPageNoWaitPrivate;

In read_local_xlog_page_no_wait:

/* If asked, let's not wait for future WAL. */
if (!wait_for_wal)
{
private_data->end_of_wal = true;
break;
}

/*
* Opaque data for callbacks to use. Not used by XLogReader.
*/
void *private_data;

Regards,
Bharath Rupireddy.