Re: POC: postgres_fdw insert batching

Hi, Tomas:
In my opinion, my patch is a little better.
Suppose one of the conditions in the if block changes in between the start
of loop and the end of the loop:

* Determine if the FDW supports batch insert and determine the batch
* size (a FDW may support batching, but it may be disabled for the
* server/table).

My patch would reflect that change. I guess this was the reason the if /
else block was placed there in the first place.

Cheers

On Wed, Jan 20, 2021 at 4:56 PM Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>
wrote:

>
>
> On 1/21/21 1:17 AM, Zhihong Yu wrote:
> > Hi,
> > The assignment to resultRelInfo is done when junk_filter_needed is true:
> >
> > if (junk_filter_needed)
> > {
> > resultRelInfo = mtstate->resultRelInfo;
> >
> > Should the code for determining batch size access mtstate->resultRelInfo
> > directly ?
> >
>
> IMO the issue is that code iterates over all plans and moves to the next
> for each one:
>
> resultRelInfo++;
>
> so it ends up pointing past the last element, hence the failures. So
> yeah, either the code needs to move before the loop (per my patch), or
> we need to access mtstate->resultRelInfo directly.
>
> I'm pretty amazed this did not crash during any of the many regression
> runs I did recently.
>
> regards
>
> --
> Tomas Vondra
> EnterpriseDB: http://www.enterprisedb.com
> The Enterprise PostgreSQL Company
>