# High load of cpu when highlight

**URL:** <https://discuss.elastic.co/t/high-load-of-cpu-when-highlight/241818>\
**Category:** Elasticsearch\
**Created:** [July 19, 2020, 10:06pm UTC](https://discuss.elastic.co/t/high-load-of-cpu-when-highlight/241818 "2020-07-19T22:06:32Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![pilo](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/pilo/32/46015_2.png) [@pilo](https://discuss.elastic.co/u/pilo)\
**Post date:** [July 19, 2020, 10:06pm UTC](https://discuss.elastic.co/t/high-load-of-cpu-when-highlight/241818/1 "2020-07-19T22:06:32Z")

</div>

Hello everyone,  
I'm having an issue when i use highlight in query.  
Currently, we are using elasticsearch for full text search on 1 index, around 10gb of documents. This index is running on a single node. Its technical information is bellow:

- 30gb ram, with 4gb heap size allocated for elasticsearch, and 2gb heap size for logstash jdbc
- 30gb ssd for around 1 index of 10gb
- CPU with two cores

Mapping of this index is like bellow:

```auto
{
  "mappings": {
    "properties": {
      "id": {
        "type": "keyword"
      },
      "translations": {
        "properties": {
          "en": {
            "properties": {
              "content": {
                "type": "keyword",
                "ignore_above": 20,
                "fields": {
                  "default": {
                    "type": "text",
                    "term_vector": "with_positions_offsets",
                    "analyzer": "indonesian"
                  },
                  "exact": {
                    "type": "text",
                    "term_vector": "with_positions_offsets",
                    "analyzer": "indonesian_exact"
                  }
                }
              },
              "title": {
                "type": "keyword",
                "ignore_above": 20,
                "fields": {
                  "default": {
                    "type": "text",
                    "term_vector": "with_positions_offsets",
                    "analyzer": "indonesian"
                  },
                  "exact": {
                    "type": "text",
                    "term_vector": "with_positions_offsets",
                    "analyzer": "indonesian_exact"
                  }
                }
              }
            }
          }
        }
      }
    }
  }
}

```

When i do a simple query string search, it took only ~200ms:

```auto
{
  "query": {
    "simple_query_string": {
      "query": "force majeur",
      "fields": [
        "translations.*.title.default",
        "translations.*.content.default"
      ]
    }
  }
}

```

But when i add 1 highlight to this query, it took around 59000ms ~ 1min, and CPU load chart in kibana suddenly goes to near 100%

```auto
{
  "query": {
    "simple_query_string": {
      "query": "foo bar",
      "fields": [
        "translations.*.title.default",
        "translations.*.content.default"
      ]
    }
  },
  "highlight": {
    "type": "fvh",
    "order": "score",
    "pre_tags": [
      "<mark>"
    ],
    "post_tags": [
      "</mark>"
    ],
    "fields": {
      "ranslations.*.content.default": {
        "fragment_size": 500,
        "number_of_fragments": 3
      }
    }
  }
}

```

I read some articles about this but i still have some questions:

- If i add more nodes to this cluster (for example 2 nodes with 1 primary shard (10gb) and 2 replica shards) then could this 3 nodes cluster accelerate the query time ?
- Does it help if i store documents in index with term vector option "with\_positions\_offsets\_payloads" instead of "with\_positions\_offsets" like the current one ?
- Does it help if i upgrade CPU from 2 cores to 4 cores ?

Highlight feature is really important in our use case. If you need more information, i'm ready to share it.  
Do you have any other suggestion to improve highlight query time ?  
Thank you alot.

---

<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [August 16, 2020, 10:19pm UTC](https://discuss.elastic.co/t/high-load-of-cpu-when-highlight/241818/2 "2020-08-16T22:19:13Z")

</div>

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