On 4/14/11 12:29 AM, Andrea Aime wrote: > On Thu, Apr 14, 2011 at 2:20 AM, Tim Schaub<[email protected]> wrote: >> WFS 2.0 describes both paging with and without transactional >> consistency. It's not a requirement to be consistent there even >> (PagingIsTransactionSafe can be true or false), right? >> >>> Also it seems that WMS GetMap already supports paging... and this is >>> more or less following suite what it is doing. >>> >>> >>> Also curious about sorting... I remember something like sorting by >>> default >>> on the feature id while paging, but my memories of it are foggy, we >>> discussed >>> this with Gabriel a loong time ago (when the paging machinery was >>> added to >>> GeoTools). >>> >>> >>> As I understand things how they are implemented now using startIndex >>> requires the underlying datastore to be able to do sorting. And when the >>> client does not specify an explicit attribute to sort on this means >>> doing a natural sort (feature id). If you look at >>> ContentFeatureSource.getReader(Query) you will see a check there. >>> >>> Which more or less means that paging can only be used with jdbc >>> datastores. Which personally I think is fine since they are the only >>> ones that can really do it efficiently. Thoughts on that? >> >> Would it be possible (later) to do sorting for all stores? I understand >> it would be inefficient, but it's a bigger drawback (in my opinion) to >> have a feature be store specific. As the client has no way to know >> about these distinctions. >
Sorry, I meant to ask about *paging* on all stores. > A trivial way to implement sorting is to do it in memory. The day someone > decides to sort on that 2GB shapefile boom! > We'd need a secondary storage sort approach (mergesort), writing one would > require quite a bit of time and the assurance everything in the feature is > serializable. > Another approach would be to have a hsql db, dump everything in it, and > make it do the sort. > > In both cases it is to be noted that we first have to sort the large > collection > and then extract the page of data we need, so in the case of the large > shapefile > you'd have to first sort everything in order to get your 50 records page. > Not efficient... (a db could do that efficiently only if it has a > index on the sorting > column, something that is normally available for the primary key) > > Cheers > Andrea > -- Tim Schaub OpenGeo - http://opengeo.org Expert service straight from the developers. ------------------------------------------------------------------------------ Benefiting from Server Virtualization: Beyond Initial Workload Consolidation -- Increasing the use of server virtualization is a top priority.Virtualization can reduce costs, simplify management, and improve application availability and disaster protection. Learn more about boosting the value of server virtualization. http://p.sf.net/sfu/vmware-sfdev2dev _______________________________________________ Geoserver-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/geoserver-devel
