[postgis-devel] SVN trunk parser modifications stage 2

[Mark Cave-Ayland]

Kevin Neufeld wrote:
> Having a new variable in the custom_variable_classes list sounds like a 
> good idea.
> 
> So, does this mean that we will be able to set the parser level for the 
> duration of the transaction? Or can this only be set for the duration of 
> the session?
> 
> SET LOCAL postgis.default_parser_check_level TO 0;
> -- or equivalently,
> SELECT set_config('postgis.default_parser_check_level', '0', true);
> 
> Cheers,
> Kevin

I now have some experimental code that uses just the plain GUC 
variables, and well... it's horrendously messy :(

The main issue is that due to PostgreSQL's delayed function loading, the 
new GUC isn't available until the first PostGIS function is called which 
causes some interesting synchronisation issues where either i) SHOW 
postgis.parser_check_level causes an ERROR if custom_variable_classes 
isn't set, and ii) changing the value using ALTER... SET cannot update 
the parser flags until the first time the parser is called. So using 
this, I was finding in testing that different combinations of commands 
in different orders would succeed or fail accordingly which is not good.

The problem with the stored procedures, of course, is that we can't 
easily reset to the default settings which makes interfacing with 
connection pooling particularly painful :(

On the basis of this, I'm now thinking that we need to take a different 
approach to get something that is going to work. I'm now thinking that 
the best way to approach this would be to tackle this from the 
input/output function perspective, perhaps having a separate function 
like ST_GeomFromTextWithStrict() or similar that will allow the correct 
strictness setting to be supplied. Then ST_GeomFromText() will remain 
OGC-compliant, while we give the user to chance to override this if 
required, much in the same way that ST_AsEWKT() works.


ATB,

Mark.

-- 
Mark Cave-Ayland
Sirius Corporation - The Open Source Experts
http://www.siriusit.co.uk
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