pre-release version 0.9 (September, 2001)
© Pedro Pereira Gonçalves (pedro@inovagis.org)
The GIServer makes use of a cache system to free system resources and minimize the WMS requests. When the GIServer receives a request it will follow a sequency of queries to the cache system. First will check if an exactly equal request was already processed. If not then the GIServer will analyse the different layers requested and will check if any of the layers was already requested. For example, if you request the layers GLOBE2.RPRAIN and TERRA.BORDERS like : REQUEST=GETMAP& LAYERS=GLOBE2.RPRAIN,TERRA.BORDERS& SRS=EPSG:4326& WIDTH=300& HEIGHT=300& FORMAT=GIF& STYLES=REFERENCE,DEFAULT& TIME=2000-08-09& BBOX=-11,34,5,50 The system will in fact cache 3 files. One for the overall request with both layers and the two other for the individual layers request. If now we should add a different request for one of the layers the cache system would return the other cached layer and saving resources and response time. For example, if now we request the same layers but with the some extra parameters for the TERRA.BORDERS layers, the GIServer will not re-request the GLOBE2.RPRAIN layer to the Globe program servers but will use instead the cached information. REQUEST=GETMAP& LAYERS=GLOBE2.RPRAIN,TERRA.BORDERS& BBOX=-10,30,70,70& SRS=EPSG:4326& WIDTH=300& HEIGHT=150& FORMAT=GIF& TERRA.BORDERS.FIELD=NAME& TERRA.BORDERS.PENSTYLE=5& The life time of this cached files is only limited by the its physical disk representation. However in some situations it might be usefull to explicitly tell the GIServer when this resource will experies. For this you can add the parameter EXPIRES to your layer request like this:
that represents the number of days that this resource is kept in cache (the integral part of this time represent the number of days, where the fractional part is fraction of a 24 hour day).
that states that the cache resource should not be used for this layer. See also: | ||||||||||||||
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