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update approx-histogram document to explain how to ignore rows with no value at ingestion time

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Himanshu Gupta 2015-08-19 15:20:37 -05:00
parent 38b8ccab04
commit 0daeb830b0
1 changed files with 7 additions and 4 deletions
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docs/content/development/approximate-histograms.md
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@ -44,14 +44,17 @@ especially with long tails, since that's where the approximation will be worse.
### Creating approxiate histogram sketches at ingestion time ### Creating approxiate histogram sketches at ingestion time
To use this feature, an "approxHistogram" aggregator must be included at To use this feature, an "approxHistogram" or "approxHistogramFold" aggregator must be included at
indexing time. The ingestion aggregator can only apply to numeric values. To indexing time. The ingestion aggregator can only apply to numeric values. If you use "approxHistogram"
query for results, an "approxHistogramFold" aggregator must be included in the then any input rows missing the value will be considered to have a value of 0, while with "approxHistogramFold"
such rows will be ignored.
To query for results, an "approxHistogramFold" aggregator must be included in the
query. query.
```json ```json
{ {
"type" : "approxHistogram(ingestion), approxHistogramFold(query)", "type" : "approxHistogram or approxHistogramFold (at ingestion time), approxHistogramFold (at query time)",
"name" : <output_name>, "name" : <output_name>,
"fieldName" : <metric_name>, "fieldName" : <metric_name>,
"resolution" : <integer>, "resolution" : <integer>,