Re: [PATCH] A hook for session start

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.

--
Craig Ringer http://www.2ndQuadrant.com/
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