On Fri, Nov 16, 2007 at 05:05:01PM +0100, hubert depesz lubaczewski wrote:
> 
> ok, but the trigger inserts column names to sl_log_x tables.

Right.  Based on you telling the trigger that the columns are there.

The trigger uses an SPI function, so that it doesn't have to look all this
stuff up all the time.  So it's cached.

But none of this is why you have to use execute script to add columns.

You have to use execute script to add columns so that the system can ensure
that the visibility rules are followed across all nodes.  This is explained
in the concepts document, which is available from the web site.  It's a
subtle problem, but one that results from the combination of async
replication, no direct back-end hooks, and MVCC.  Please go and read that
concepts document before raising this thread again.  If you show evidence of
having read it, maybe Jan will reply to you instead, because he's in a
better position to explain much of this than I am.

A

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Andrew Sullivan
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