Robert Haas <robertmhaas@gmail.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
regards, tom lane
