Re: Parallel Inserts in CREATE TABLE AS

On Thu, May 27, 2021 at 10:27 AM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
> On Thu, May 27, 2021 at 10:16 AM Bharath Rupireddy
> <bharath(dot)rupireddyforpostgres(at)gmail(dot)com> wrote:
> >
> > On Thu, May 27, 2021 at 7:12 AM houzj(dot)fnst(at)fujitsu(dot)com
> > <houzj(dot)fnst(at)fujitsu(dot)com> wrote:
> > > I am afraid that the using the FSM seems not get a stable performance gain(at least on my machine),
> > > I will take a deep look into this to figure out the difference. A naive idea it that the benefit that bulk extension
> > > bring is not much greater than the cost in FSM.
> > > Do you have some ideas on it ?
> >
> > I think, if we try what Amit and I said in [1], we should get some
> > insights on whether the bulk relation extension is taking more time or
> > the FSM lookup. I plan to share the testing patch adding the timings
> > and the counters so that you can also test from your end. I hope
> > that's fine with you.
>
> I think some other cause of contention on relation extension locks are
> 1. CTAS is using a buffer strategy and due to that, it might need to
> evict out the buffer frequently for getting the new block in. Maybe
> we can identify by turning off the buffer strategy for CTAS and
> increasing the shared buffer so that data fits in memory.
>

One more thing to ensure is whether all the workers are using the same
access strategy?

--
With Regards,
Amit Kapila.