Re: [Proposal] Fully WAL logged CREATE DATABASE - No Checkpoints

Hi,

On 2022-08-07 09:24:40 +0530, Dilip Kumar wrote:
> On Sat, Aug 6, 2022 at 9:36 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >
> > Dilip Kumar <dilipbalaut(at)gmail(dot)com> writes:
> > > On Fri, Aug 5, 2022 at 10:43 AM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> > >> Yeah maybe it is not necessary to close as these unowned smgr will
> > >> automatically get closed on the transaction end.
> >
> > I do not think this is a great idea for the per-relation smgrs created
> > during RelationCopyStorageUsingBuffer. Yeah, they'll be mopped up at
> > transaction end, but that doesn't mean that creating possibly tens of
> > thousands of transient smgrs isn't going to cause performance issues.

I was assuming that the files would get reopened at the end of the transaction
anyway, but it looks like that's not the case, unless wal_level=minimal.

Hm. CreateAndCopyRelationData() calls RelationCreateStorage() with
register_delete = false, which is ok because createdb_failure_callback will
clean things up. But that's another thing that's not great for a routine with
a general name...

> Okay, so for that we can simply call smgrcloserellocator(rlocator);
> before exiting the RelationCopyStorageUsingBuffer() right?

Yea, I think so.

> > I think RelationCopyStorageUsingBuffer needs to open and then close
> > the smgrs it uses, which means that ReadBufferWithoutRelcache is not the
> > appropriate API for it to use, either; need to go down another level.
>
> Not sure how going down another level would help, the whole point is
> that we don't want to keep the reference of the smgr for a long time
> especially in the loop which is interruptible.

Yea, I'm not following either.

Greetings,

Andres Freund