March 2021
Intermediate to advanced
265 pages
6h 50m
Chinese
Content preview from Presto实战
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44
｜
第
4
章
4.7
查询执行模型
你已经了解，在实际使用中，
Presto
通常部署为包含一个协调器和多个工作节点的集群。
接下来介绍
Presto
如何处理实际的
SQL
查询语句。
有关
Presto
的
SQL
支持的更多细节，请参见第
8
章和第
9
章。
执行模型是在
Presto
中进行查询性能调优必备的基础知识。
回忆一下，终端用户通过
CLI
、
使用
ODBC
或
JDBC
的客户端或其他客户端库发送
SQL
语句到协调器，协调器之后调用工作节点从数据源获得数据、创建结果数据集并将结果返
回给客户端。
我们先仔细了解一下协调器内部的情况。
SQL
语句首先以文本形式提交到协调器
，协调器
解析和分析这条语句，之后创建一个由
Presto
内部数据结构表示的执行计划
，叫作
查询计划
。
图
4-6
展示了这一流程
。查询计划全面地表示了一条
SQL
语句处理数据和返回结果所需进
行的步骤。
解析器/分析器 计划器/优化器
图 4-6：处理一条 SQL 查询语句并创建查询计划
如图
4-7
所示，查询计划生成过程利用了元数据
SPI
和数据统计
SPI
来创建查询计划。也
就是说，协调器会使用
SPI
直接连接到数据源，以收集有关表和其他元数据的信息。
协调器
元数据SPI
解析器/分析器 计划器/优化器 调度器
数据统计SPI 数据位置SPI
图 4-7：查询计划和调度的 SPI
Prest ...
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.