Re: BUG #17798: Incorrect memory access occurs when using BEFORE ROW UPDATE trigger

On Mon, Apr 3, 2023 at 2:29 PM Richard Guo <guofenglinux(at)gmail(dot)com> wrote:

> Reproduced this issue on master with your queries. I looked into this
> issue and I agree with your analysis. I think this is exactly what
> happened.
>
> I also agree that we should materialize the newslot before we fetch
> trigtuple from the oldslot which would materialize the oldslot and
> release all buffer pins. But I'm not too familiar with the arounding
> codes so need someone else to have a look.
>

I have a second look at this issue and now I think the fix in v1 patch
is correct. I think the comment needs to be updated for this change,
maybe something like

* (Typically, newslot was also generated by ExecGetUpdateNewTuple, so
* that epqslot_clean will be that same slot and the copy step below
- * is not needed.)
+ * is not needed. And we need to materialize newslot in this case,
+ * since its tuple might be dependent on oldslot's storage, which
+ * might not be a local copy and be freed before we fetch newslot's
+ * tuple.)

Thanks
Richard