[mapserver-users] Need advice to support caching mechanism
paulborodaev at gmail.com
Mon Mar 16 03:59:23 EDT 2009
I need to debate web map images caching technique. I'm using OpenLayers with
tiled mapserver layer. But now I dissatisfied mapserver image request url
scheme because it has variable map config file name (path) as a part
(parameter), and some may be some other variable parts (for ex. OL use
random '_olSalt' parameter to force HTTPRequest layer map redraw, time
stamps, session id's etc.). I decide to change this scheme to have constant
url for map image tile of the same bbox (extent), config & data 'stamps' to
support browser caching. Map file can be constant but not in 'true'
multiuser environment where they are customized for each user needs,
according their rights (privileges). So map file name vary often by session
(id) indirectly. We can exclude other url variables painlessly. Final tasks:
- overwraiting some OL code to build correct url
- create http handler to wrap mapserver cgi (and may be support intranet
- but how to provide some hash key for mapserver (all layers/styles...)
config and data 'stamps'.
Currently (for test purpose) I use CRC32 of map SLD as this hash. I can
support versioning with some 'seed'
metadata in map file for config and/or in (spatial-) database for data (for
each layer in service table 'data_version'). Seed (version info) will be
changed (by some way) after each 'publishing operation'.
May be another way exists (other comprehensive map object string
serialization/dumping to calculate checksum from it, some wms/wfs command)?
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