Re: [PATCH] A hook for session start

On Fri, 21 Jul 2017 09:53:19 +0800
Craig Ringer <craig(at)2ndquadrant(dot)com> wrote:

> On 21 July 2017 at 08:42, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> > On Thu, Jul 20, 2017 at 8:27 AM, Fabrízio de Royes Mello
> > <fabriziomello(at)gmail(dot)com> wrote:
> > > I'm not sure your real needs but doesn't it material for improve Event
> > > Triggers???
> >
> > I've thought about that, too. One problem is what to do if the user
> > hits ^C while the event trigger procedure is running. If you respond
> > to that by killing the event trigger and letting the user issue
> > commands, then the event trigger can't be used for security or
> > auditing purposes because the user might prevent it from doing
> > whatever it's intended to do with a well-timed interrupt. If you
> > ignore ^C or make it turn into FATAL, then a poorly-crafted trigger
> > can lock users out of the database. Maybe that's OK. We could say
> > "well, if you lock yourself out of the database with your logon
> > trigger, you get to shut down the database and restart in single user
> > mode to recover".
> >
> > A hook, as proposed here, is a lot simpler and lacks these concerns.
> > Installing code in C into the database is intrinsically risky
> > anywhere, and not any moreso here than elsewhere. But it's also less
> > accessible to the average user.
> > <http://www.postgresql.org/mailpref/pgsql-hackers>
>
>
> I'd favour the c hook personally. It's a lot more flexible, and can be used
> by an extension to implement trigger-like behaviour if anyone wants it,
> including the extension's choice of error handling decisions.
>
> It's also a lot simpler and less intrusive for core. Which is nice where we
> don't have something that we don't have anything compelling destined for
> core that needs it. (I want to add a bunch of hooks in the logical
> replication code in pg11 for similar reasons, and so features like DDL
> replication can be prototyped as extensions more practically).
>
> That said, isn't ExecutorStart_hook + ProcessUtility_hook able to serve the
> same job as a session-start hook, albeit at slightly higher overhead? You
> can just test to see if your initial tasks have run yet.

Thank you for your suggestion. Certainly, we can do the similar job of a
session-start hook using these existing hooks, although these hooks are
triggered when the first query is executed not when the session is started.
Now I come to think that an additional hook is not need.

Thanks,

>
> --
> Craig Ringer http://www.2ndQuadrant.com/
> PostgreSQL Development, 24x7 Support, Training & Services

--
Yugo Nagata <nagata(at)sraoss(dot)co(dot)jp>