The confusion of elasticsearch?


(famoss) #1

After read the document of the es,There are some confusion about it.

doc_values built at a document index time on not text field,save data in disk.

fielddata built at query time,save data in memory.If a field cached,when the new docs has the field add to the fielddata cache?

doc_values and fielddata are both a cache,are used mainly when sorting on or computing aggregations on a field?

query cache,Only save the query result,only the same dsl can use it?

Es has any other cache?


(Daniel Mitterdorfer) #2

Hi @famoss,

you cannot exactly say that "doc values" are a cache. Doc values are a data structure that is optimized for an access pattern "document" -> "list of terms" which is needed for e.g. sorting and aggregations. The implementation of doc values relies on the operating systems "page cache" which maps pages from disk to memory as needed. Also field data is a data structure.

We have:

You can also check the Definitive Guide which explains a lot of concepts in great detail.

Daniel


(system) #3

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