CODEWITHSUNDEEP
elasticsearch
Kramer Li
Kramer Li

Reputation: 2476

What does Elasticsearch 5 do under the hood when sorting?

I read below words on Elasticsearch docs.

https://www.elastic.co/guide/en/elasticsearch/reference/5.4/search-request-sort.html#_memory_considerations

When sorting, the relevant sorted field values are loaded into memory. This means that per shard, there should be enough memory to contain them.

This is different from my understanding about sorting. I thought that some datatype, keyword for example, should already be sorted since Elasticsearch will create index on them. These already sorted fields should not need to be load into memory to sort again.

So am I understand right?

Upvotes: 1

Views: 157

Answers (1)

xeraa
xeraa

Reputation: 10859

Index in relational databases means B* tree and that is indeed sorted.

Index in Elasticsearch is where you store your data; previously we compared that to a table in the relational world but for various reasons this is not really true, so let's not use that as a direct comparison. Except for the index-time sorting Val mentioned above, an index is not stored as a sorted data structure based on a specific field. However, some fields can be used efficiently for sorting (like numeric data types or not analyzed text). And this is where the memory consideration from above comes into play.

Upvotes: 0

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