Re: Heap truncation without AccessExclusiveLock (9.4)

On Mon, May 20, 2013 at 10:19 AM, Heikki Linnakangas
<hlinnakangas@vmware.com> wrote:
>> It shouldn't be difficult to restrict the set of backends that have to
>> be signaled to those that have the relation open.  You could have a
>> special kind of catchup signal that means "catch yourself up, but
>> don't chain"
>
> What does "chain" mean above?

Normally, when sinval catchup is needed, we signal the backend that is
furthest behind.  After catching up, it signals the backend that is
next-furthest behind, which in turns catches up and signals the next
laggard, and so forth.

> Hmm. The sinval message makes sure that when a backend locks a relation, it
> will see the latest value, because of the AcceptInvalidationMessages call in
> LockRelation. If there is no sinval message, you'd need to always check the
> shared memory area when you lock a relation.

The latest value of what?

-- 
Robert Haas
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