Re: ALTER TABLE lock strength reduction patch is unsafe

From: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
To: Bruce Momjian <bruce(at)momjian(dot)us>
Cc: Simon Riggs <simon(at)2ndQuadrant(dot)com>, Peter Geoghegan <pg(at)heroku(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Noah Misch <noah(at)leadboat(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: ALTER TABLE lock strength reduction patch is unsafe
Date: 2014-01-28 17:36:36
Message-ID: 20140128173636.GR10723@eldon.alvh.no-ip.org
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Bruce Momjian escribió:

> > I have no problem removing the parameter if required to. In that case,
> > I would like to leave the parameter in until mid beta, to allow
> > greater certainty.

Uhm. If we remove a GUC during beta we don't need to force an initdb.
At worst we will need to keep a no-op GUC variable that is removed in
the next devel cycle. That said, if we're going to have a GUC that's
going to disappear later, I think it's better to wait for 2 releases as
proposed, not remove mid-beta.

> > In any case, I would wish to retain as a minimum an extern bool
> > variable allowing it to be turned off by C function if desired.

I think this amounts to having an undocumented GUC that is hard to
change. I prefer the GUC, myself.

> Anything changed to postgresql.conf during beta is going to require an
> initdb.
> Also, lots of backward-compatibility infrastructure, as you are
> suggesting above, add complexity to the system.
>
> I am basically against a GUC on this. We have far larger problems with
> 9.3 than backward compatibility, and limited resources.

If we have a clear plan on removing the parameter, it's easy enough to
follow through. I don't think lack of resources is a good argument,
because at that point there will be little to discuss and it's an easy
change to make. And I think the plan is clear: if no bug is found the
parameter is removed. If a bug is found, it is fixed and the parameter
is removed anyway.

Honestly, I would prefer that we push a patch that has been thoroughly
reviewed and in which we have more confidence, so that we can push
without a GUC. This means mark in CF as needs-review, then some other
developer reviews it and marks it as ready-for-committer.

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

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