Re: Largeobject Access Controls (r2460)

On Fri, Dec 18, 2009 at 9:51 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> Part of what I'm confused about (and what I think should be documented
>> in a comment somewhere) is why we're using MVCC visibility in some
>> places but not others.  In particular, there seem to be some bits of
>> the comment that imply that we do this for read but not for write,
>> which seems really strange.  It may or may not actually be strange,
>> but I don't understand it.
>
> It is supposed to depend on whether you opened the blob for read only
> or for read write.  Please do not tell me that this patch broke that;
> because if it did it broke pg_dump.
>
> This behavior is documented at least here:
> http://www.postgresql.org/docs/8.4/static/lo-interfaces.html#AEN36338

Oh, I see. Thanks for the pointer. Having read that through, I can
now say that the comments in the patch seem to imply that it attempted
to preserve those semantics, but I can't swear that it did. I will
take another look at it, but it might bear closer examination by
someone with more MVCC-fu than myself.

...Robert