postgresql | 易学教程

How does a Django UUIDField generate a UUID in Postgresql?

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问题 After reading this blog post https://blog.starkandwayne.com/2015/05/23/uuid-primary-keys-in-postgresql/ I wanted to know more about how Django generates uuid because I am using them as my pk. Well, according to the docs, https://docs.djangoproject.com/es/1.9/ref/models/fields/#uuidfield, Django is relying on the Python UUID module https://docs.python.org/3/library/uuid.html#uuid.UUID. But there are many kinds of UUID, and it is not at all clear to me which one is being generated in Django, or

How to connect to Postgres in GithHub Actions

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问题 I am trying GitHub Actions for CI with a Ruby on Rails application. My setup is with VM, not running the Ruby build in a container. This is my workflow yml. It runs all the way without errors until the step "Setup Database". name: Rails CI on: push: branches: - master pull_request: branches: - master jobs: build: runs-on: ubuntu-latest services: postgres: image: postgres:10.10 env: POSTGRES_USER: postgres POSTGRES_PASSWORD: postgres POSTGRES_DB: db_test ports: - 5432/tcp options: --health-cmd

connect google cloud sql postgres instance from beam pipeline

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问题 I want to connect google cloud sql postgres instance from apache beam pipeline running on google dataflow. I want to do this using Python SDK. I am not able to find proper documentation for this. In cloud SQL how to guide I dont see any documentation for dataflow. https://cloud.google.com/sql/docs/postgres/ Can someone provide documentation link/github example? 回答1: You can use the relational_db.Write and relational_db.Read transforms from beam-nuggets as follows: First install beam-nuggests:

Linux内存管理（最透彻的一篇）【转】

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转自： https://www.cnblogs.com/ralap7/p/9184773.html 摘要：本章首先以应用程序开发者的角度审视Linux的进程内存管理，在此基础上逐步深入到内核中讨论系统物理内存管理和内核内存的使用方法。力求从外到内、水到渠成地引导网友分析Linux的内存管理与使用。在本章最后，我们给出一个内存映射的实例，帮助网友们理解内核内存管理与用户内存管理之间的关系，希望大家最终能驾驭Linux内存管理。前言内存管理一向是所有操作系统书籍不惜笔墨重点讨论的内容，无论市面上或是网上都充斥着大量涉及内存管理的教材和资料。因此，我们这里所要写的Linux内存管理采取避重就轻的策略，从理论层面就不去班门弄斧，贻笑大方了。我们最想做的和可能做到的是从开发者的角度谈谈对内存管理的理解，最终目的是把我们在内核开发中使用内存的经验和对Linux内存管理的认识与大家共享。当然，这其中我们也会涉及到一些诸如段页等内存管理的基本理论，但我们的目的不是为了强调理论，而是为了指导理解开发中的实践，所以仅仅点到为止，不做深究。遵循“理论来源于实践”的“教条”，我们先不必一下子就钻入内核里去看系统内存到底是如何管理，那样往往会让你陷入似懂非懂的窘境（我当年就犯了这个错误！）。所以最好的方式是先从外部（用户编程范畴）来观察进程如何使用内存，等到大家对内存的使用有了较直观的认识后

Return updated row attributes on UPDATE

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问题 My query is as follow: UPDATE t1 SET t1.foreign_key = (SELECT id FROM t2 WHERE t2.col = %s ) WHERE t1.col = %s How do I return some attributes of the updated row in the table in the same query? 回答1: Use the RETURNING clause. The optional RETURNING clause causes UPDATE to compute and return value(s) based on each row actually updated. Any expression using the table's columns, and/or columns of other tables mentioned in FROM , can be computed. The new (post-update) values of the table's columns

Return updated row attributes on UPDATE

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Return updated row attributes on UPDATE

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Slow PostgreSQL query in production - help me understand this explain analyze output

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问题 I have a query that is taking 9 minutes to run on PostgreSQL 9.0.0 on x86_64-unknown-linux-gnu, compiled by GCC gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-46), 64-bit This query is automatically generated by hibernate for my application. It's trying to find all of the "teacher members" in a school. A membership is a user with a role in a group. There are several types of groups, but here what matters are schools and services. If someone is a teacher member in a service and a member in this

Slow PostgreSQL query in production - help me understand this explain analyze output

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Handling race conditions in PostgreSQL

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问题 I have several workers, each holding its own connection to PostgreSQL. The workers manipulate with different tables. The workers handle parallel requests from outside the system. One of the tables being accessed is the table of users. When some information comes, I first need to ensure there is a record for the user in the table. If there is no record, I wish to create one at first. I'm using the following idiom: if [user does not exist] then [create user] The code of [user does not exist] is