Re: Locking for Rename To new_name works differently for different objects

On Wed, Oct 15, 2014 at 10:04 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Amit Kapila <amit.kapila16@gmail.com> writes:
>> I have observed that for renaming some of the objects
>> AccessExclusiveLock is taken on object whereas for
>> other kind of objects no lock is taken on object before
>> renaming the object.
>
> The usual theory for DDL updates of all types (not just rename)
> is that an explicit lock is only needed for objects whose catalog
> representation comprises more than one row.  Otherwise, the implicit
> locking involved in updating that row is sufficient to serialize
> different updates.

That's an interesting point that I hadn't considered, but I'm willing
to believe that at least some of the differences might also be
haphazard.

-- 
Robert Haas
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