Re: [Proposal] Adding callback support for custom statistics kinds

> + if (kind_info->from_serialized_extra_stats)
> + {
> + if (!kind_info->from_serialized_extra_stats(&key, header, fpin))
> + {
> + elog(WARNING, "could not read extra stats for entry %u/%u/%" PRIu64,
> + key.kind, key.dboid, key.objid);
> + goto error;
> + }
> + }
> ```
>
> When deserialize failed, it goes to error. In the error clause, it calls pgstat_reset_after_failure(), so do we want to give extensions a chance to do some reset operations? If yes, then we can add a reset_after_failure() callback.

The way v5 is dealing with a deserialize failure is that when
it goes to error, the pgstat_reset_after_failure() will reset the
stats for all kinds, since pgstat_drop_all_entries() is called
during that call. So there is nothing for an extension to have
to do on its own. The extension will then clean-up resources
at the end when all the kinds are iterated over and
kind_info->end_extra_stats(STATS_READ) is called for each
kind.

Let me know if I'm still missing something?

--
Sami Imseih
Amazon Web Services (AWS)