【Elasticsearch】检索高亮_elasticsearch 高亮

2.案例实战

2.1 测试数据准备

首先，我们创建一个名为 blog_posts 的索引，并插入一些测试数据：

PUT /blog_posts{ \"mappings\": { \"properties\": { \"title\": { \"type\": \"text\" }, \"content\": { \"type\": \"text\" }, \"author\": { \"type\": \"keyword\" }, \"views\": { \"type\": \"integer\" }, \"publish_date\": { \"type\": \"date\" }, \"tags\": { \"type\": \"keyword\" } } }}

POST /blog_posts/_bulk{\"index\":{}}{\"title\":\"Elasticsearch Basics\",\"content\":\"Learn the basics of Elasticsearch and how to perform simple queries.\",\"author\":\"John Doe\",\"views\":1500,\"publish_date\":\"2023-01-15\",\"tags\":[\"search\",\"database\"]}{\"index\":{}}{\"title\":\"Advanced Search Techniques\",\"content\":\"Explore advanced search techniques in Elasticsearch including aggregations and filters.\",\"author\":\"Jane Smith\",\"views\":3200,\"publish_date\":\"2023-02-20\",\"tags\":[\"search\",\"advanced\"]}{\"index\":{}}{\"title\":\"Data Analytics with ELK\",\"content\":\"How to use the ELK stack for data analytics and visualization.\",\"author\":\"John Doe\",\"views\":2800,\"publish_date\":\"2023-03-10\",\"tags\":[\"analytics\",\"elk\"]}{\"index\":{}}{\"title\":\"Elasticsearch Performance Tuning\",\"content\":\"Tips and tricks for optimizing Elasticsearch performance in production environments.\",\"author\":\"Mike Johnson\",\"views\":4200,\"publish_date\":\"2023-04-05\",\"tags\":[\"performance\",\"optimization\"]}{\"index\":{}}{\"title\":\"Kibana Dashboard Guide\",\"content\":\"Creating effective dashboards in Kibana for monitoring and analysis.\",\"author\":\"Jane Smith\",\"views\":1900,\"publish_date\":\"2023-05-12\",\"tags\":[\"kibana\",\"visualization\"]}

2.2 基础高亮语法

默认情况下，不指定参数。但其实，此时 fragment_size 默认为 $100$，number_of_fragments 默认为 $5$。

GET /blog_posts/_search{ \"query\": { \"match\": { \"content\": \"Elasticsearch\" } }, \"highlight\": { \"fields\": { \"content\": {} } }}

2.3 自定义高亮标签

GET /blog_posts/_search{ \"query\": { \"match\": { \"content\": \"techniques\" } }, \"highlight\": { \"pre_tags\": [\"\"], \"post_tags\": [\"\"], \"fields\": { \"content\": { \"fragment_size\": 150, \"number_of_fragments\": 3 } } }}

2.4 多字段高亮

GET /blog_posts/_search{ \"query\": { \"multi_match\": { \"query\": \"search\", \"fields\": [\"title\", \"content\"] } }, \"highlight\": { \"fields\": { \"title\": {}, \"content\": { \"fragment_size\": 100, \"number_of_fragments\": 2 } } }}

2.5 返回完整字段内容

设置 number_of_fragments 为 $0$，适用于短文本，如标题。

GET /blog_posts/_search{ \"query\": { \"match\": { \"title\": \"Kibana\" } }, \"highlight\": { \"fields\": { \"title\": { \"number_of_fragments\": 0 } } }}

2.6 长文本多匹配点场景

模拟长文本字段：

POST /blog_posts/_update/Nmgc2ZcB9mA5oeTvZT0A{ \"doc\": { \"content\": \"Elasticsearch is a tool. Elasticsearch is fast. Elasticsearch scales well. Repeat: Elasticsearch is a tool.\" }}

GET /blog_posts/_search{ \"query\": { \"match\": { \"content\": \"Elasticsearch\" } }, \"highlight\": { \"fields\": { \"content\": { \"fragment_size\": 30, \"number_of_fragments\": 3 } } }}

展示前 $3$ 个匹配点（忽略第 $4$ 个重复匹配）。

2.7 限制片段数量和大小

每个片段限制在 $30$ 字符以内，只返回 $2$ 个片段（即使实际匹配更多）。

GET /blog_posts/_search{ \"query\": { \"match\": { \"content\": \"Elasticsearch\" } }, \"highlight\": { \"fields\": { \"content\": { \"fragment_size\": 30, \"number_of_fragments\": 2 } } }}

如果不设置 number_of_fragments 参数，默认值为 $5$，此处会全部返回。

GET /blog_posts/_search{ \"query\": { \"match\": { \"content\": \"Elasticsearch\" } }, \"highlight\": { \"fields\": { \"content\": { \"fragment_size\": 30 } } }}

3.为什么有时片段长度会超过 fragment_size

即使设置了 fragment_size，实际返回的片段长度可能会略大，原因包括：

• 单词完整性保护：Elasticsearch 不会在单词中间截断，因此会扩展到下一个空格或标点符号。

  // 设 fragment_size=20，匹配词为\"Elasticsearch\"\"This is a test with Elasticsearch and other words\"→ 可能返回：\"test with Elasticsearch and other\"（实际27字符）

• 高亮标签占用长度：HTML 高亮标签（如 ）会增加额外字符，但这些 不计入 fragment_size。
• 边界扩展策略：为保证上下文可读性，Elasticsearch 可能会稍微扩展片段范围。

PUT /test/_doc/1{ \"text\": \"Elasticsearch is a distributed search engine. It is built on top of Lucene. Elasticsearch provides powerful full-text search capabilities. Many companies use Elasticsearch for log analytics.\"}

GET /test/_search{ \"query\": { \"match\": { \"text\": \"Elasticsearch\" } }, \"highlight\": { \"fields\": { \"text\": { \"fragment_size\": 20, \"number_of_fragments\": 2 } } }}

\"highlight\": { \"text\": [ \"Elasticsearch is a\", // 实际21字符（含空格） \"use Elasticsearch for\" // 实际22字符 ]}

GET /test/_search{ \"query\": { \"match\": { \"text\": \"search\" } }, \"highlight\": { \"fields\": { \"text\": { \"fragment_size\": 10, \"number_of_fragments\": 1 } } }}

\"highlight\": { \"text\": [ \"distributed search engine\" // 实际25字符（远超10） ]}