Hi all,
I would like to submit the proposal of a new community module to add a distributed caching level to the GeoServer back-end when serving GridCoverages.
This means that raster data composing GridCoverages will be cached in order to avoid repeated read accesses when serving same data. This will reduce time consumption needed to go to the fileSystem/remote disks to get the data bytes or access the DB, parse metadata (CRS, format tags), perform subsampling/oversampling on the read data, assemble different pieces of different images to create the coverage (as for the ImageMosaic case made of multiple granules).
This will be supported by adding a pluggable module (as an extension point) implementing a GridCoverageReaderCallback interface which provides CachingGridCoverageReader instances (implementing GridCoverage2DReader) to the ResourcePool.
Whenever a read operation is performed, it leverages on the cache to setup the requested GridCoverage. Raster data (RenderedImage) composing the GridCoverage are managed through GeoWebCache entities (TileLayer, GridSet, GridSetBroker, BlobStore and derived ones) so we can leverage on well-known/well-tested paradigms.
The underlying coverage read operations (which occurs when data is not available in cache) will be made through WCS requests (in order to get raw GridCoverage data satisfying the requested parameters). Therefore, the caching machinery will deal with a WCSLayer object (extending the abstract GWC TileLayer class), which will retrieve ConveyorTile objects used by the reader to be assembled as parts of the requested coverage.
Last step will be integrating a distributed caching mechanism (as Hazelcast) on the underlying BlobStore structures: that is already under development as part of a work Nicola is doing on GeoWebCache 1.
More documentation will be ready in a couple of hours.
Feedbacks are welcome.
Daniele Romagnoli
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Ing. Daniele Romagnoli
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