[QGIS-trac] Re: [Quantum GIS] #3200: Feature cache

[Quantum GIS]

#3200: Feature cache
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   Reporter:  wonder                            |              Owner:  wonder       
       Type:  enhancement                       |             Status:  new          
   Priority:  major: does not work as expected  |          Milestone:  Version 1.7.0
  Component:  Vectors                           |            Version:               
   Keywords:                                    |   Platform_version:               
   Platform:  All                               |           Must_fix:  No           
Status_info:  0                                 |  
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Comment(by wonder):

 It should be also noted that this patch has been developed by Andrej
 Krutak (not me!) within qgis-mapper project.

 Some notes for the author:

  * The "Cache nothing" option completely disables caching and features are
 always retrieved from data provider.
  * The "Heuristics" option keeps reasonable amount of features in memory,
 by releasing some of them when the current extent is much smaller than the
 cached area.
  * The "Cache all layer's features" option allows cache to store all
 features displayed. This doesn't neccesarily mean that all vector layers'
 data will be cached - once the cache is enabled, it only holds features
 from the biggest extent displayed (i.e. if user zooms-out, and required
 data are superset of the currently cached data extent - the cache is freed
 and refilled with the superset data - which are of course read from the
 data provider). Also, if user moves current extent, so that the already
 cached extent only partially overlaps with the new one, the previous data
 will be released and the new extent cached. This "filling behaviour" is
 the same as the one of "Heuristics" option.

-- 
Ticket URL: <http://trac.osgeo.org/qgis/ticket/3200#comment:3>
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