App-schema: get numberOfFeatures without executing the query
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Key: GEOT-3302
URL: http://jira.codehaus.org/browse/GEOT-3302
Project: GeoTools
Issue Type: Improvement
Components: core xml
Reporter: Rini Angreani
Assignee: Rini Angreani
To support streaming of features, GeoServer WFS writes the root element of a
response and then each feature as it is created. The root element requires a
numberOfFeatures element; because the number of features is not known,
GeoServer must get them all to count them. It then must get them all a second
time to encode them one by one. (Streaming is needed as not all responses will
fit in memory.) The consequence of the double query is that WFS responses take
twice as long. This is particularly bad for app-schema as it is already very
slow.
In practice, GeoServer streams features to disk first, so that an error
document can be returned if an error occurs. (This is a selectable output
strategy.)
In theory it should be possible to stream only the features to disk as an XML
fragment, then encode the root element on the fly when all the features have
been seen, meaning the numberOfFeatures is known, and only one query is
required.
This may require modification to Encoder, OutputStrategy, and OutputFormat
APIs.
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