493 lines
14 KiB
Markdown
493 lines
14 KiB
Markdown
# ElasticSearch
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## 简介
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ElasticSearch是一个分布式的搜索和分析引擎、可缩放的数据存储、矢量数据库（vector database）。
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### 用例场景
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如下是ElasticSearch的用例场景
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- 日志：es可以用于收集、存储和分析日志
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- full-text search：通过倒排索引，es可以用于构建全文本搜索方案
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### 安装
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下列安装示例基于Ubuntu 22.04
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#### add elasticsearch GPG keys
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```bash
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wget -q https://artifacts.elastic.co/GPG-KEY-elasticsearch -O- | sudo gpg --dearmor -o /usr/share/keyrings/elasticsearch-keyring.gpg
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```
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#### Add Elasticsearch 8.x APT Repository
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```bash
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echo "deb [signed-by=/usr/share/keyrings/elasticsearch-keyring.gpg] https://artifacts.elastic.co/packages/8.x/apt stable main" | sudo tee /etc/apt/sources.list.d/elastic-8.x.list
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```
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#### install elastic search
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```bash
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sudo apt update && sudo apt install elasticsearch
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```
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### Indices, documents, and fields
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在ES中，index是存储的基本单元，是存储数据的逻辑namespace，位于同一index下的存储数据共享相似的特征。
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在ES服务部署之后，需要创建index，并在index中存储数据。
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index是一系列document的集合，通过`name`或`alias`唯一标识，在查询或其他操作中，通过`unique name`来定位index。
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#### Documents and fields
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ElasticSearch以json文档的格式来序列化和存储数据。一个document是fields的集合，field则是对应的key-value pair。每个document都有一个唯一的id，文档id可以手动指定，也可以让ES自动生成。
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一个ES文档的格式如下所示：
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```json
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{
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"_index": "my-first-elasticsearch-index",
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"_id": "DyFpo5EBxE8fzbb95DOa",
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"_version": 1,
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"_seq_no": 0,
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"_primary_term": 1,
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"found": true,
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"_source": {
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"email": "john@smith.com",
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"first_name": "John",
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"last_name": "Smith",
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"info": {
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"bio": "Eco-warrior and defender of the weak",
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"age": 25,
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"interests": [
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"dolphins",
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"whales"
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]
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},
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"join_date": "2024/05/01"
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}
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}
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```
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#### metadata field
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一个indexed document包含data和metadata。
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metadata fields为系统fields，用于存储document的相关信息，在elastic search中，metadata field以下划线`_`开头，例如，如下field为metadata field：
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- `_id`：文档id，文档id在每个index中都是唯一的
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- `_index`：标识该文档存储在哪个index中
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#### Mappings and data types
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每个index都有mapping或schema，用于指定document中的fields如何被索引。
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一个`mapping`定义了每个field的data type，以及该field如何被索引、该field如何被存储。
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在将document添加到index时，对于`mapping`有如下两种选择：
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- `Dynamic Mapping`：让ES自动检测data type并创建mapping。在引入dynamic mapping后，可能会针对某些用例场景产生次优结果
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- `Explicit Mapping`：针对每个field手动指定data type
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### 向ElasticSearch中添加数据
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#### General content
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General content是不包含时间戳的数据，对于general content，可以通过如下方式添加到ES中：
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- API：可以通过HTTP API向ES中添加数据
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#### Timestamped data
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Timestamped data代表包含timestamp field的数据，如果使用了`Elastic Common Schema(ECS)`，那么timestamp field的名称为`@timestamp`，这些数据可能是`logs, metrics, traces`。
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### 查询和分析数据
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可以通过如下方式来查询和分析数据
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#### Rest Api
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可以通过rest api来管理elastic search集群，并索引和查询数据。
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#### query language
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ES提供了多种查询语言来和数据进行交互
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- Query DSL: ES主要的查询语言
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- ES|QL: 8.11中新增的piped query language和计算引擎
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##### Query DSL
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query DSL是一种json格式的查询语言，支持复杂的查询、过滤、聚合操作，是ES最原始也是功能最强的查询语言
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`_search` endpoint接收Query DSL格式的查询
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query DSL支持如下查询：
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- 全文本搜索：搜索已经被分析和索引过的文本，支持短语或临近查询、模糊匹配等
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- 关键词查询：支持精确的关键词匹配
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- 语义查询
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- 向量查询
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- 地理位置查询
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##### Query DSL分析
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如果要通过Query DSL对elastic search数据进行分析，那么Aggregations是主要的工具。
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Aggregations允许根据数据构建复杂的数据摘要，并获取指标、模式和趋势。
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aggregations利用了和查询相同的数据结构，故而聚合的速度十分快，可以实时的对数据进行分析和可视化。
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在使用ES时，可以在同一时刻对相同的数据同时进行文档查询、结果过滤、数据分析操作，聚合是在查询请求的上下文中进行计算的。
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ES支持如下类型的Aggregations：
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- Metric：计算metrics，例如field的总和或平均
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- Bucket：基于field value、范围或其他指标对文档进行分组
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- Pipeline：在其他聚合操作结果集的基础上执行聚合操作
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##### ES | QL
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Elasticsearch Query Language是一个piped query language，用于对数据进行过滤、transforming、分析。ES|QL基于新的计算引擎，查询、聚合、transformation方法是直接在Elasticsearch中执行的。在Kibana工具中可以使用ES|QL语法。
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ES|QL支持Query DSL中的部分特性，例如聚合、过滤、transformation
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## 使用ElasticSearch Api索引和查询数据
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### 创建索引
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可以通过如下方式来创建一个名为`books`的索引：
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```
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PUT /books
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```
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返回相应结构如下，代表索引创建成功：
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```json
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{
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"acknowledged": true,
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"shards_acknowledged": true,
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"index": "books"
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}
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```
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### 向索引中添加数据
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可以向ElasticSearch中添加json形式的数据，json格式数据被称为document。ElasticSearch将添加的数据保存到可搜索的索引中。
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#### 向索引中添加单个document
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```
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POST books/_doc
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{
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"name": "Snow Crash",
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"author": "Neal Stephenson",
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"release_date": "1992-06-01",
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"page_count": 470
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}
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```
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该请求的返回体中包含ElasticSearch为该document生成的元数据，包含索引范围内唯一的`_id`，在索引范围内唯一标识该document。
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```json
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{
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"_index": "books",
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"_id": "O0lG2IsBaSa7VYx_rEia",
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"_version": 1,
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"result": "created",
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"_shards": {
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"total": 2,
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"successful": 2,
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"failed": 0
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},
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"_seq_no": 0,
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"_primary_term": 1
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}
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```
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#### 向索引中添加多个document
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可以使用`/_bulk`接口来在单个请求中添加多个document。`_bulk`请求的请求体由多个json串组成，json串之间通过换行符分隔。
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bulk请求示例如下所示：
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```
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POST /_bulk
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{ "index" : { "_index" : "books" } }
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{"name": "Revelation Space", "author": "Alastair Reynolds", "release_date": "2000-03-15", "page_count": 585}
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{ "index" : { "_index" : "books" } }
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{"name": "1984", "author": "George Orwell", "release_date": "1985-06-01", "page_count": 328}
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{ "index" : { "_index" : "books" } }
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{"name": "Fahrenheit 451", "author": "Ray Bradbury", "release_date": "1953-10-15", "page_count": 227}
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{ "index" : { "_index" : "books" } }
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{"name": "Brave New World", "author": "Aldous Huxley", "release_date": "1932-06-01", "page_count": 268}
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{ "index" : { "_index" : "books" } }
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{"name": "The Handmaids Tale", "author": "Margaret Atwood", "release_date": "1985-06-01", "page_count": 311}
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```
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如果上述请求被正确处理，将会得到如下返回体：
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```json
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{
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"errors": false,
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"took": 29,
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"items": [
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{
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"index": {
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"_index": "books",
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"_id": "QklI2IsBaSa7VYx_Qkh-",
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"_version": 1,
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"result": "created",
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"_shards": {
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"total": 2,
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"successful": 2,
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"failed": 0
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},
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"_seq_no": 1,
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"_primary_term": 1,
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"status": 201
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}
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},
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{
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"index": {
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"_index": "books",
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"_id": "Q0lI2IsBaSa7VYx_Qkh-",
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"_version": 1,
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"result": "created",
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"_shards": {
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"total": 2,
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"successful": 2,
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"failed": 0
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},
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"_seq_no": 2,
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"_primary_term": 1,
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"status": 201
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}
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},
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{
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"index": {
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"_index": "books",
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"_id": "RElI2IsBaSa7VYx_Qkh-",
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"_version": 1,
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"result": "created",
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"_shards": {
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"total": 2,
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"successful": 2,
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"failed": 0
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},
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"_seq_no": 3,
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"_primary_term": 1,
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"status": 201
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}
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},
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{
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"index": {
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"_index": "books",
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"_id": "RUlI2IsBaSa7VYx_Qkh-",
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"_version": 1,
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"result": "created",
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"_shards": {
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"total": 2,
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"successful": 2,
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"failed": 0
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},
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"_seq_no": 4,
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"_primary_term": 1,
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"status": 201
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}
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},
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{
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"index": {
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"_index": "books",
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"_id": "RklI2IsBaSa7VYx_Qkh-",
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"_version": 1,
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"result": "created",
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"_shards": {
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"total": 2,
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"successful": 2,
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"failed": 0
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},
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"_seq_no": 5,
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"_primary_term": 1,
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"status": 201
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}
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}
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]
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}
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```
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### 定义mapping和data type
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#### 使用dynamic mapping
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当使用dynamic mapping时，elastic search默认情况下将会自动为新field创建mapping。上述示例中向索引中添加的document都使用了dynamic mapping，因为在创建索引时，并没有手动指定mapping。
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可以向`books`索引中新增一个document，新增document中包含当前索引documents中不存在的字段：
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```
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POST /books/_doc
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{
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"name": "The Great Gatsby",
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"author": "F. Scott Fitzgerald",
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"release_date": "1925-04-10",
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"page_count": 180,
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"language": "EN"
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}
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```
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此时，针对`books`索引，新字段`language`之前并不存在，会以`text`的data type被新增到mapping中。
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可以通过`/{index_uid}/_mapping`请求来查看索引的mapping信息：
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```
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GET /books/_mapping
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```
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其返回的响应为：
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```json
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{
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"books": {
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"mappings": {
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"properties": {
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"author": {
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"type": "text",
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"fields": {
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"keyword": {
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"type": "keyword",
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"ignore_above": 256
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}
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}
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},
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"name": {
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"type": "text",
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"fields": {
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"keyword": {
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"type": "keyword",
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"ignore_above": 256
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}
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}
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},
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"new_field": {
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"type": "text",
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"fields": {
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"keyword": {
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"type": "keyword",
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"ignore_above": 256
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}
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}
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},
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"page_count": {
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"type": "long"
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},
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"release_date": {
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"type": "date"
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}
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}
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}
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}
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}
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```
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#### 手动指定索引的mapping
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如下示例会展示如何在创建索引时手动指定索引的mapping：
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```
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PUT /my-explicit-mappings-books
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{
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"mappings": {
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"dynamic": false,
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"properties": {
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"name": { "type": "text" },
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"author": { "type": "text" },
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"release_date": { "type": "date", "format": "yyyy-MM-dd" },
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"page_count": { "type": "integer" }
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}
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}
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}
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```
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上述示例中请求体含义如下：
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- `"dynamic": false`: 在索引中禁用dynamic mapping，如果提交的document中包含了mapping中不存在的field，那么该提交的document将会被拒绝
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- `"properties"`：properties属性定义了document中的fields及其数据类型
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#### 将dynamic mapping和手动指定mapping相结合
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如果在创建索引时手动指定了索引的mapping，那么在向索引中添加document时，document必须符合索引的定义。
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如果要结合dynamic mapping和手动指定mapping，有如下两种方式：
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- 使用update mapping Api
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- 手动指定mapping时，将dynamic设置为true，此时向document中添加new field时无需对mapping执行update
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### 搜索索引
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#### 搜索所有文档
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```
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GET books/_search
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```
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上述请求将会搜索`books`索引中所有的文档
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响应如下：
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```json
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{
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"took": 2,
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"timed_out": false,
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"_shards": {
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"total": 5,
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"successful": 5,
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"skipped": 0,
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"failed": 0
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},
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"hits": {
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"total": {
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"value": 7,
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"relation": "eq"
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},
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"max_score": 1,
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"hits": [
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{
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"_index": "books",
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"_id": "CwICQpIBO6vvGGiC_3Ls",
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"_score": 1,
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"_source": {
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"name": "Brave New World",
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"author": "Aldous Huxley",
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"release_date": "1932-06-01",
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"page_count": 268
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}
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},
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... (truncated)
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]
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}
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}
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```
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其中，响应体的字段含义如下：
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- `took`：es执行该搜索请求花费的时间，单位为ms
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- `time_out`：代表该请求是否超时
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- `_shards`：代表该请求的分片数和成功数
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- `hits`：hits对象中包含了执行结果
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- `total`：total对象中包含了匹配结果的总数信息
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- `max_score`：max_score包含了在所有匹配documents中最高的relavance score
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- `_index`：该字段代表了document所属的索引
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- `_id`：该字段代表document的唯一标识id
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- `_score`：`_score`字段代表当前document的relavance score
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- `_source`：该字段包含了indexing过程中提交的原始json对象
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#### match请求
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可以通过match请求来查询特定field中包含指定值的documents。这是全文本查询的标准查询。
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如下示例中会查询索引中`name` field中包含`brave`的文档：
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```
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GET books/_search
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{
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"query": {
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"match": {
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"name": "brave"
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}
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}
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}
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```
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响应体结构如下：
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```json
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{
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"took": 9,
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"timed_out": false,
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"_shards": {
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"total": 5,
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"successful": 5,
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"skipped": 0,
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"failed": 0
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},
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"hits": {
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"total": {
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"value": 1,
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"relation": "eq"
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},
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"max_score": 0.6931471,
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"hits": [
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{
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"_index": "books",
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"_id": "CwICQpIBO6vvGGiC_3Ls",
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"_score": 0.6931471,
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"_source": {
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"name": "Brave New World",
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"author": "Aldous Huxley",
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"release_date": "1932-06-01",
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"page_count": 268
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}
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}
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]
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}
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||
}
|
||
```
|
||
|
||
#### 删除索引
|
||
如果要删除创建的索引从头开始，可以使用如下方式：
|
||
```
|
||
DELETE /books
|
||
DELETE /my-explicit-mappings-books
|
||
```
|
||
删除索引将会永久删除其document、shards、元数据。
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|