Showing entries 1 to 10 of 1070
10 Older Entries »
Displaying posts with tag: sql (reset)
InnoDB: running out of AUTO_INCREMENT values

Most InnoDB primary keys are built on integer columns with the AUTO_INCREMENT option (which is a very good practice for reasons that are outside of the purpose of this article). But we have to monitor that we are not going to run out of AUTO_INCREMENT value. If this happens, we will get errors like this:

ERROR 167 (22003): Out of range value for column 'a' at row 1

Obviously, when creating tables, we should use a type that is sufficiently big, and make it UNSIGNED to avoid wasting half of its space. But there are also some details about AUTO_INCREMENT that we should remember.

First, the values to monitor are not MAX(id), but they are the AUTO_INCREMENT column in information_schema

[Read more]
Prepared Statements in MariaDB 10.2

Prepared statements are particularly useful in stored procedures. In fact, they are the only way to execute dynamic SQL, which means that, for example, the list of ORDER BY columns is in a variable. You can do this by composing an SQL string, as you do in other languages.

However, in MySQL and up to MariaDB 10.1, there are some annoying limitations:

  • Prepared statements exist at a connection level. Even if you declare them in a stored procedure, they are global. If you are writing a stored procedure which should be usable in many contexts (maybe it’s part of an open source library), there is a risk that you overwrite existing prepared statements. There is no way to get a list of existing prepared statements.
  • A prepared statement is prepared from a literal string or a user variable. A literal string cannot contain variables. A user variable exists at a session level, so again, there is a risk to overwrite …
[Read more]
What’s Next for SQL Databases?

In this blog, I’ll go over my thoughts on what we can expect in the world of SQL databases.

After reading Baron’s prediction on databases, here:

https://www.xaprb.com/blog/defining-moments-in-database-history/

I want to provide my own view on what’s coming up next for SQL databases. I think we live in interesting times, when we can see the beginning of the next-generation of RDBMSs.

There are defining characteristics of such databases:

  1. Auto-scaling. The ability to add and use resources depending on the current load and database size. This is done transparently for users and DBAs.
  2. Auto-healing. The automatic handling of node …
[Read more]
How does a relational database work

Introduction While doing my High-Performance Java Persistence training, I came to realize that it’s worth explaining how a relational database works, as otherwise, it is very difficult to grasp many transaction-related concepts like atomicity, durability, and checkpoints. In this post, I’m going to give a high-level explanation of how a relational database works internally while … Continue reading How does a relational database work →

Superset: Scaling Data Access and Visual Insights at Airbnb

By Alanna Scott, Bogdan Kyryliuk, Eli Brumbaugh, Jeff Feng, Max Beauchemin and Vera Liu

Introduction

At Airbnb, one of our fundamental beliefs is that data access should be democratized to empower every employee in order to make data informed decisions. We believe that grounding decisions with quantitative insights from data, together with qualitative insights (e.g. in-person user research) result in the best possible business decisions. This applies to all parts of the organization, whether it is about deciding to launch a new product …

[Read more]
MySQL Reporting using AutoSQL Tool

Three ways to schedule a MySQL query

If you walk through any office you see people working in Excel. With MySQL for Excel (https://www.mysql.com/why-mysql/windows/excel/) you can already let them pull information from Excel themselves. However, in some cases it saves a lot of time if they don’t have to pull the information, but it’s pushed automatically.
Exception lists are the best examples of queries you want to push to users. If you have a query with occasional results, you don’t want to check for this every day. In this case you just want to receive a mail if there are any results. Eg a list of stuck invoices which can’t be processed automatically.
How can we do this?

1. Using the MySQL Event Scheduler

The MySQL Event scheduler can be used to run a query on a predefined schedule and output the results in CSV format. …

[Read more]
A beginner’s guide to the Phantom Read anomaly, and how it differs between 2PL and MVCC

Introduction Unlike SQL Server which, by default, relies on the 2PL (Two-Phase Locking) to implement the SQL standard isolation levels, Oracle, PostgreSQL, and MySQL InnoDB engine use MVCC (Multi-Version Concurrency Control). However, providing a truly Serializable isolation level on top of MVCC is really difficult, and, in this post, I’ll demonstrate that it’s very difficult … Continue reading A beginner’s guide to the Phantom Read anomaly, and how it differs between 2PL and MVCC →

Some observations on MySQL to sqlite migration & compatibility

I'm experimenting with sqlite as backend database for orchestrator. While orchestrator manages MySQL replication topologies, it also uses MySQL as backend. For some deployments, and I'm looking into such one, having MySQL as backend is a considerable overhead.

This sent me to the route of looking into a self contained orchestrator binary + backend DB. I would have orchestrator spawn up its own backend database instead of connecting to an external one.

Why even relational?

Can't orchestrator just use a key-value backend?

Maybe it could. But frankly I enjoy the power of relational databases, and the versatility they offer has proven itself multiple times with orchestrator, being able to answer …

[Read more]
MySQL group replication: installation with Docker

Overview

MySQL Group Replication was released as GA with MySQL 5.7.17. It is essentially a plugin that, when enabled, allows users to set replication with this new way.

There has been some confusion about the stability and usability of this release. Until recently, MySQL Group Replication (MGR) was only available in the Labs, which traditionally denotes a preview or an use-at-your-own-risk feature. Several months ago we saw the release of Group Replication as a Docker image, which allowed users to deploy a peer-to-peer cluster (every node is a master.) However, about one month after such release, word came from Oracle discouraging this setup, and inviting users to use Group Replicator in …

[Read more]
Query Language Type Overview

This blog provides a query language type overview.

The idea for this blog originated from some customers asking me questions. When working in a particular field, you often a dedicated vocabulary that makes sense to your peers. It often includes phrases and abbreviations because it’s efficient. It’s no different in the database world. Much of this language might make sense to DBA’s, but it might sound like “voodoo” to people not used to it. The overview below covers the basic types of query languages inside SQL. I hope it clarifies what they mean, how they’re used and how you should interpret them.

DDL (Data Definition Language)

A database schema is a visualization of information. It contains the data structure separated by tables structures, views and anything that contains structure …

[Read more]
Showing entries 1 to 10 of 1070
10 Older Entries »