Re: Bus error in pg_logical_slot_get_changes (9.4.7, sparc)

On 2016-04-14 15:14:37 -0400, Tom Lane wrote:
> I've been looking around and testing some more. I noticed that the only
> caller of ReorderBufferRestoreChange always passes a maxaligned buffer,
> so most of the changes I suggested are unnecessary. AFAICT, it's only
> the second fetch of t_len that is at any risk.

I think so too. And I agree that a comment about this would have been
rather helpful...

> Even there, at least in
> HEAD, I cannot construct a test case in which the first tuple's t_len is
> not a multiple of 4.

That's really kinda weird. It's a tuple from WAL, and the length's from
the record; the same way wal replay gets it. Wonder if this might not
indicate a relevant bug somewhere...

> I have a suspicion that
> something in the impenetrable thicket that passes for prefix/suffix
> optimization in log_heap_update is forcing the WAL-logged tuple length to
> be rounded off to sizeof(int) (*not* MAXALIGN).

I don't think so, because the prefix optimization is essentially
disabled for logical...

> So I now think my previous patch is overkill, and we should instead use
> something like the attached.

Looks good to me. Thanks!

- Andres