Use half floats for most floating point numbers#1941
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ruflin merged 1 commit intoelastic:masterfrom Jul 4, 2016
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Starting with 5.0.0-alpha4, Elasticsaerch supports half floats. [Half precision floating-point](https://en.wikipedia.org/wiki/Half-precision_floating-point_format) numbers have good precision for small numbers, but they degrade for larger numbers. This is switching to half floats all the fields that are percentages (values between 0 and 1) and the fields that were floats but have naturally small values only. After going through the list, most of our floating point number fit in one of these categories. Only 3 float fields were left untouched. The template generator automatically switches to "float" when generating the ES 2.x template files.
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jenkins, retest it |
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Thanks a lot for taking this one. |
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I'm curious whether this significatly reduces the size of indices? |
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See also elastic/elasticsearch#19264. |
jpountz
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Jul 18, 2016
This is a tentative to revive elastic#15939 motivated by elastic/beats#1941. Half-floats are a pretty bad option for storing percentages. They would likely require 2 bytes all the time while they don't need more than one byte. So this PR exposes a new `scaled_float` type that requires a `scaling_factor` and internally indexes `value*scaling_factor` in a long field. Compared to the original PR it exposes a lower-level API so that the trade-offs are clearer and avoids any reference to fixed precision that might imply that this type is more accurate (actually it is *less* accurate). In addition to being more space-efficient for some use-cases that beats is interested in, this is also faster that `half_float` unless we can improve the efficiency of decoding half-float bits (which is currently done using software) or until Java gets first-class support for half-floats.
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Starting with 5.0.0-alpha4, Elasticsearch supports half floats.
Half precision floating-point numbers
have good precision for small numbers, but the precision degrades fast for larger numbers.
This is switching to half floats all the fields that are percentages
(values between 0 and 1) and the fields that were floats but have naturally
small values only. After going through the list, most of our floating point
numbers fit in one of these categories. Only 3 float fields were left untouched.
The template generator automatically switches to "float" when generating the
ES 2.x template files.
This closes #1936.