Re: Parallel Inserts in CREATE TABLE AS

On Wed, Dec 30, 2020 at 10:47 AM Bharath Rupireddy
<bharath(dot)rupireddyforpostgres(at)gmail(dot)com> wrote:
>
> On Wed, Dec 30, 2020 at 10:32 AM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> > I have completed reviewing 0001, I don't have more comments, just one
> > question. Soon I will review the remaining patches.
>
> Thanks.
>
> > + /* If parallel inserts are to be allowed, set a few extra information. */
> > + if (myState->is_parallel)
> > + {
> > + myState->object_id = intoRelationAddr.objectId;
> > +
> > + /*
> > + * We don't need to skip contacting FSM while inserting tuples for
> > + * parallel mode, while extending the relations, workers instead of
> > + * blocking on a page while another worker is inserting, can check the
> > + * FSM for another page that can accommodate the tuples. This results
> > + * in major benefit for parallel inserts.
> > + */
> > + myState->ti_options = 0;
> >
> > Is there any performance data for this or just theoretical analysis?
>
> I have seen that we don't get much performance with the skip fsm
> option, though I don't have the data to back it up. I'm planning to
> run performance tests after the patches 0001, 0002 and 0003 get
> reviewed. I will capture the data at that time. Hope that's fine.
>

When you run the performance tests, you can try to capture and publish
relation size & the number of pages that are getting created for base
table and the CTAS table, you can use something like SELECT relpages
FROM pg_class WHERE relname = 'tablename & SELECT
pg_total_relation_size('tablename'). Just to make sure that there is
no significant difference between the base table and CTAS table.

Regards,
Vignesh
EnterpriseDB: http://www.enterprisedb.com