[mapserver-dev] Single pass query concerns (RFC-52)
szekerest at gmail.com
Sat Mar 6 16:05:19 EST 2010
I've been thinking about the single pass query implementation in the MSSQL
2008 driver. I would probably implement a block cursor which would provide
to access client side rowsets with multiple rows in a randomly fashion (by
positioning with SQLSetPos)
Regardless of the approach chosen, it seems I'd have to do something
different for the rowsets to support positioning, than the current forward
only single row approach. I don't think it would be reasonable to use the
same approach in all cases, I would prefer:
1. Using the forward only single row appoach (providing a smaller memory
footprint at the driver) for drawing the background maps (with all features
in the current extent)
2. Using the block cursor to retrieve the results of a query and implement
LayerResultsGetShape (probably keeping a smaller amout of rows in memory) .
Currently we don't have an option to distinguish between the purpose of a
particular WhichShapes operation, in this regard I would like to have to
have some additional info in either the LayerOpen or the LayerWhichShapes
call which would denote whether futher LayerResultsGetShape(s) will be taken
into action within the current result set or not.
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