Re: ALTER TABLE lock strength reduction patch is unsafe

On 28 January 2014 17:15, Bruce Momjian <bruce@momjian.us> wrote:
> On Tue, Jan 28, 2014 at 04:36:39PM +0000, Simon Riggs wrote:
>> For me, reducing the strength of DDL locking is a major change in
>> RDBMS behaviour that could both delight and surprise our users. Maybe
>> a few actually depend upon the locking behaviour, maybe. After some
>> years of various people looking at this, I think we've got it right.
>> Experience tells me that while I think this is the outcome, we are
>> well advised to protect against the possibility that it is not correct
>> and that if we have corner case issues, it would be good to easily
>> disable this in the field. In the current case, a simple parameter
>> works very well to disable the feature; in other cases, not.
>>
>> Summary: This is an atypical case. I do not normally propose such
>> things - this is the third time in 10 years, IIRC.
>
> Uh, in my memory, you are the person who is most likely to suggest a
> GUC of all our developers.

(smiles) I have suggested parameters for many features, mostly in the
early days of my developments before I saw the light if autotuning.
But those were control parameters for tuning features. So yes, I have
probably introduced more parameters than most, amongst the many things
I've done. I'm guessing you don't recall how much trouble I went to in
order to allow sync rep to have only 1 parameter, c'est la vie.

What I'm discussing here is a compatibility parameter to allow new
features to be disabled. This would be the third time in 10 years I
suggested a parameter for that reason, i.e. one that the user would
hardly ever wish to set.

-- Simon Riggs                   http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services