Re: [HACKERS] Block level parallel vacuum

On Tue, Jan 14, 2020 at 4:17 PM Mahendra Singh Thalor
<mahi6run(at)gmail(dot)com> wrote:
>
> Hi,
>
> + /*
> + * Try to initialize the parallel vacuum if requested
> + */
> + if (params->nworkers >= 0 && vacrelstats->useindex)
> + {
> + /*
> + * Since parallel workers cannot access data in temporary tables, we
> + * can't perform parallel vacuum on them.
> + */
> + if (RelationUsesLocalBuffers(onerel))
> + {
> + /*
> + * Give warning only if the user explicitly tries to perform a
> + * parallel vacuum on the temporary table.
> + */
> + if (params->nworkers > 0)
> + ereport(WARNING,
> + (errmsg("disabling parallel option of vacuum
> on \"%s\" --- cannot vacuum temporary tables in parallel",
>
> From v45 patch, we moved warning of temporary table into
> "params->nworkers >= 0 && vacrelstats->useindex)" check so if table
> don't have any index, then we are not giving any warning. I think, we
> should give warning for all the temporary tables if parallel degree is
> given. (Till v44 patch, we were giving warning for all the temporary
> tables(having index and without index))
>

I am not sure how useful it is to give WARNING in this case as we are
anyway not going to perform a parallel vacuum because it doesn't have
an index? One can also say that WARNING is expected in the cases
where we skip a parallel vacuum due to any reason (ex., if the size of
the index is small), but I don't think that will be a good idea.

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com