redistributed table中的数据放在临时文件么?

In Greenplum, when data is redistributed during a Redistribute Motion, the data is not stored in temporary files on disk in the traditional sense. Instead, the data is sent directly to the target segments over the network and processed in memory. Here's how it works:

  1. Hash Calculation:

    • Each segment calculates the hash value of the specified key (e.g., cust_id) for each row in the table being redistributed (e.g., sales).
  2. Data Transfer:

    • Rows are sent from the originating segment to the appropriate target segment based on the calculated hash value. This transfer happens over the network and is managed by the interconnect layer.
  3. Receiving Segments:

    • When a segment receives a row, it does not recompute the hash value. Instead, it directly processes the incoming row in memory. The receiving segment then uses this data for further operations, such as joins or aggregations.

Temporary Files and Tablespaces

While the redistributed data itself is not stored in temporary files, Greenplum does use temporary tablespaces for other purposes, such as:

  • Temporary Tables : When creating temporary tables or indexes, Greenplum can use the temp_tablespaces configuration parameter to specify where these temporary objects are stored.

  • Spill Files : For operations like hash aggregates or hash joins that require sorting large datasets, Greenplum may create temporary spill files. These spill files are also stored in the tablespaces specified by temp_tablespaces.

Example Configuration

You can configure the temp_tablespaces parameter to control the location of temporary objects:

复制代码
SET temp_tablespaces = 'fastspace';

This command sets the temporary tablespace to fastspace, which can be a tablespace created for faster access and processing of temporary data.

Conclusion

During a Redistribute Motion, the data is sent directly to the target segments and processed in memory without being stored in temporary files on disk. However, Greenplum does use temporary tablespaces for other temporary objects and spill files, which can be configured using the temp_tablespaces parameter.

相关推荐
ChinaRainbowSea1 分钟前
7. LangChain4j + 记忆缓存详细说明
java·数据库·redis·后端·缓存·langchain·ai编程
小马学嵌入式~1 小时前
嵌入式 SQLite 数据库开发笔记
linux·c语言·数据库·笔记·sql·学习·sqlite
Java小白程序员1 小时前
MyBatis基础到高级实践:全方位指南(中)
数据库·mybatis
Monly212 小时前
人大金仓:merge sql error, dbType null, druid-1.2.20
数据库·sql
不宕机的小马达2 小时前
【Mysql|第一篇】Mysql的安装与卸载、Navicat工具的使用
数据库·mysql
float_六七2 小时前
数据库连接池:性能优化的秘密武器
数据库·oracle·性能优化
码界奇点2 小时前
MongoDB vs MySQLNoSQL与SQL数据库的架构差异与选型指南
数据库·sql·mongodb·系统架构
IT 小阿姨(数据库)2 小时前
PgSQL中pg_stat_user_tables 和 pg_stat_user_objects参数详解
linux·运维·数据库·sql·postgresql·oracle
倔强的石头_2 小时前
Windows系统下KingbaseES数据库保姆级安装教程(附常见问题解决)
数据库
麦兜*3 小时前
MongoDB 常见错误解决方案:从连接失败到主从同步问题
java·数据库·spring boot·redis·mongodb·容器