Re: [PATCH] A hook for session start

On Fri, Jul 21, 2017 at 9:35 AM, Yugo Nagata <nagata(at)sraoss(dot)co(dot)jp> wrote:
>
> 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).
> >

I agree with you both...

> > 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.
>

As Nagata said hooks proposed by Craing will happens only when the first
query is called so I don't know how it works for session start... are we
missing something?

If we're going to add this hook what about add a session end hook also?

Regards,

--
Fabrízio de Royes Mello
Consultoria/Coaching PostgreSQL
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