What kind of filters are really cached?

Elastic Stack Elasticsearch
1

Hi,
I am building queries so that i can take advantage of query caching.
I need to know, how to write a filter so that it can be cached.
Can someone please help me if the below will be cached ?

{
	"query": {
		"bool": {
			"must": [
				// Some queries
			],
			"filter": [
				{
					"term": {
						"type": {
							"value": "Cars",
							"boost": 1.0
						}
					}
				}
			]
		}
	}
}

When i run the above my cached index with same documents and cache disabled index with same documents gives exactly same throughput. The queryCache size goes upto 50Mb.

I am not able to understand why my caching and its utilization is not working.
Please help !

2

Why do you think cache is not working? I mean can you give details about your test?

3

I have two separate ES clusters:
Cluster A - "queries.cache.enable=false" - 35million docs
Cluster B - "queries.cache.enable=true" - 35million docs

The only difference in A and B is cache, rest everything is exactly same.

Test -
I have test queries like above of ~3lakh records. I run it against A and then B.
The throughput i get is exactly same.

Cached details:
I can see data cached on A is 0kb and on B is 100mb. So some queries are getting cached on B for sure.

Query:
Why is ES not utilizing the cache and giving me better performance on B ?

4

Most of the cache used is the file system cache. @jpountz can tell more on this topic hopefully.

5

Thanks. I thought it was in-memory cache as it would use some part of assigned heap. Not sure though.

@jpountz, any help would be appreciated. We are stuck on a important issue on production.

6

There are several caches, a shard request cache, a filter cache, plus Elasticsearch heavily relies on the OS cache.

Term filters are never cached, for a good reason: the inverted index is already a cache of hits for every possible term. So if all your queries look like the one you shared, it's expected that the query cache doesn't help.

7

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