Hi, Aleksey!

On Dec 27, Aleksey Midenkov wrote:
> > >
> > > MDEV-15458 Segfault in heap_scan() upon UPDATE after ADD SYSTEM VERSIONING
> > >
> > > * HA_EXTRA_REMEMBER_POS, HA_EXTRA_RESTORE_POS for HEAP storage engine
> > > * Versioning tests support
> >
> > As far as I can see, there are two approaches to fixing this bug.
> > And if we go the way of HA_EXTRA_REMEMBER_POS/HA_EXTRA_RESTORE_POS then
> > your fix is good.
> >
> > But I'd still like to understand whether write_row is supposed to
> > disturb the scan. Why should heap_write() overwrite
> > info->current_ptr=pos and info->current_hash_ptr? Inserting a row
> > doesn't happen at the "current position", so I don't quite understand
> > why it modifies current_ptr at all. There is no functionality like
> > "continue the scan from the last inserted row", right? It just doesn't
> > make sense to me.
> 
> I don't know why it works like this, maybe to keep consistency at API
> level: we insert record and then we able to access it without search.
> HEAP storage was copypasted from MyISAM where `lastpos` analogy also
> is updated at mi_write(). Without updating `current_ptr` and `lastpos`
> tests don't fail (main, funcs_1, heap). But I can't say whether the
> performance is affected and how it will go in production.

Thanks for the idea.
I've tried to fix handler::write_row to not reset the scan.
This, indeed, worked. I've also asked Monty and he also was of the
opinion that handler::write_row should not reset the scan.

I've pushed into a stage tree a fix with your test cases. Let's see how
it'll go.

Regards,
Sergei
Chief Architect MariaDB
and secur...@mariadb.org

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