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From: Dimitri Fontaine <dimitri@2ndQuadrant.fr>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Thom Brown <thom@linux.com>
Cc: Dimitri Fontaine <dimitri@2ndquadrant.fr>
Cc: pgsql-hackers@postgresql.org, Andres Freund <andres@anarazel.de>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Subject: Re: Command Triggers, patch v11
Date: Fri, 09 Mar 2012 18:29:55 +0100
Message-ID: <m2eht1ptrg.fsf@2ndQuadrant.fr> (raw)
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References: <m24nufq466.fsf@2ndQuadrant.fr>
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Robert Haas <robertmhaas@gmail.com> writes:
> I'm not convinced.  Right now, it's fairly useless - all the triggers
> could possibly do is throw an error, and an error is going to get
> thrown anyway, so it's only a question of which error message the user
> will see.  But we discussed before the idea of adding a capability for
> BEFORE triggers to request that the actual execution of the command
> get skipped, and then it's possible to imagine this being useful.
> Someone could even use a command trigger that detects which machine
> it's running on, and if it's the standby, uses dblink to execute the
> command on the master, or something crazy like that.  Command triggers
> could also be useful for logging all attempts to execute a particular
> command, which is probably still appropriate on the standby.

There are some other use cases, like using plsh to go apt-get install an
extension's package when you see the master just created it, so that
your read only queries on the hot standby have a chance of loading the
code you need.

Regards,
--
Dimitri Fontaine
http://2ndQuadrant.fr     PostgreSQL : Expertise, Formation et Support



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  Cc: dimitri@2ndQuadrant.fr, robertmhaas@gmail.com, thom@linux.com, andres@anarazel.de, tgl@sss.pgh.pa.us
  Subject: Re: Command Triggers, patch v11
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