Different results for same query


#1

Hi,

Using kibana 6.0.1.

I get different results when running the same question on the same data multiple times:

on left side the the value for 25th and 50th percentile havent been changed, although no new data has been inserted.

How comes?

Regards, Andreas


(Spencer Alger) #2

Checkout https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations-metrics-percentile-aggregation.html#search-aggregations-metrics-percentile-aggregation-approximation or information about the algorythm elasticsearch uses to calculate percentiles at scale, and how it is generally best consider them approximations.

I'm not sure why that would lead to different values being produced on the exact same data (assuming you didn't reindex the data, which might lead to slightly different sharding), but if you move the questing over to the elasticsearch section someone might be able to tell you.


#3

can anyone here can give more details? should i open a bug at github?


(Mark Harwood) #4

The sequence in which the same set of documents are provided to the percentiles aggregation can lead to minor variations in results.
The insertion sequence can be affected by:

  1. Primary and replica shards having different physical arrangements of content on disk (Lucene merge operations are non-deterministic)
  2. The sequence of merging results from multiple shards (again, a non-deterministic order)

(system) #5

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