[mapserver-dev] [performance] mapserver list expressions

[Daniel Morissette]

+1 on the addition.

Bonus points if we could get a simple RFC to document and keep a trace 
of the addition. The contents of this email with a tiny bit of editing 
might be enough, it's just that having it in a RFC would be easier than 
looking for it in a ticket or the list archives, and would allow us to 
refer to this RFC as a one of the new features at release time.

My 0.02$

Daniel


On 13-04-03 11:16 AM, thomas bonfort wrote:
> While profiling the openstreetmap renderings, I found a relatively low
> hanging performance speedup related to expressions when doing class
> filtering. The context relates to when you'd need to apply a given CLASS
> to multiple attribute values.
> Currently, to apply a single class to multiple values of an attribute,
> you can either use regular expressions, or use the IN operator, like this:
>
> LAYER
>    ...
>    CLASSITEM "type"
>    CLASS
>      EXPRESSION /primary|secondary|tertiary/  #regular expression on
> CLASSITEM
>      EXPRESSION ("[type]" IN "primary,secondary,tertiary") #"complex"
> parser expression
>      ...
>    END
> END
>
> Both methods require quite a bit of overhead, either in the regex system
> calls, or by using quite a few mallocs when going through the IN parser
> operation.
>
> We can cut down on this overhead by adding a "list" expression type,
> denoted by the { } delimiters, where the previous layer definition becomes:
>
>   LAYER
>    ...
>    CLASSITEM "type"
>    CLASS
>      EXPRESSION {primary,secondary,tertiary}
>      ...
>    END
> END
>
> The modifications to the code are fairly straightforward, and no
> backwards incompatibilities are expected as this is a new functionality
> that does not collide with previous mapserver expressions.
> The changes can be seen here:
> https://github.com/tbonfort/mapserver/commit/fae435d17b099485ab6792bfae3a7d8dd8992b4c
> . (you can ignore the changes to mapparser.*, they correct a bug in the
> IN parser and aren't related to the list operator)
>
> Our parser guru is OK with these changes, so I would like to vote to
> include this new expression for our 6.4 release.
>
> I'll start with my +1
>
> best regards,
> thomas
>
>
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>


-- 
Daniel Morissette
http://www.mapgears.com/
Provider of Professional MapServer Support since 2000