[DOCS] Add some documentation about the performance of `_source` usage in scripts.
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@ -184,6 +184,12 @@ source field is loaded per doc, parsed, and then provided to the script
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for evaluation. The `_source` forms the context under which the source
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for evaluation. The `_source` forms the context under which the source
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field can be accessed, for example `_source.obj2.obj1.field3`.
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field can be accessed, for example `_source.obj2.obj1.field3`.
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Accessing `_source` is much slower compared to using `_doc`
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but the data is not loaded into memory. For a single field access `_fields` may be
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faster than using `_source` due to the extra overhead of potentially parsing large documents.
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However, `_source` may be faster if you access multiple fields or if the source has already been
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loaded for other purposes.
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[float]
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[float]
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=== mvel Built In Functions
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=== mvel Built In Functions
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