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Displaying posts with tag: Oracle (reset)
A beginner’s guide to database deadlock

Introduction In this article, we are going to see how a deadlock can occur in a relational database system, and how Oracle, SQL Server, PostgreSQL, or MySQL recover from a deadlock situation. Database locking Relational database systems use various locks to guarantee transaction ACID properties. For instance, no matter what relational database system you are using, locks will always be acquired when modifying (e.g., UPDATE or DELETE) a certain table record. Without locking a row that was modified by a currently running transaction, Atomicity would be compromised. Using locking for controlling access... Read More

The post A beginner’s guide to database deadlock appeared first on Vlad Mihalcea.

JDBC Driver Maven dependency list

Introduction Ever wanted to connect to a relational database using Java and didn’t know which JDBC Driver Maven dependency to use? If so, this article is surely going to help you from now on. Oracle Since September 2019, the Oracle JDBC Driver is available on Maven Central. For JDK 10 and 11, use the following Maven dependency: For JDK 8, use the ojdbc8 artifact instead: For more details about the proper version to use, check out the following Maven Central link. MySQL The MySQL Driver is available on Maven Central, so just... Read More

The post JDBC Driver Maven dependency list appeared first on Vlad Mihalcea.

Session Variables

In MySQL and Oracle, you set a session variable quite differently. That means you should expect there differences between setting a session variable in Postgres. This blog post lets you see how to set them in all three databases. I’m always curious what people think but I’m willing to bet that MySQL is the simplest approach. Postgres is a bit more complex because you must use a function call, but Oracle is the most complex.

The difference between MySQL and Postgres is an “@” symbol versus a current_setting() function call. Oracle is more complex because it involves the mechanics in Oracle’s sqlplus shell, SQL dialect, and PL/SQL language (required to assign a value to a variable).

MySQL

MySQL lets you declare a session variable in one step and use it one way in a SQL statement or stored procedure.

  1. You set a session variable on a single line with the following …
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What’s Faster? COUNT(*) or COUNT(1)?

One of the biggest and undead myths in SQL is that COUNT(*) is faster than COUNT(1). Or was it that COUNT(1) is faster than COUNT(*)? Impossible to remember, because there’s really no reason at all why one should be faster than the other. But is the myth justified?

Let’s measure!

How does COUNT(…) work?

But first, let’s look into some theory. The two ways to count things are not exactly the same thing. Why?

  • COUNT(*) counts all the tuples in a group
  • COUNT(<expr>) counts all the tuples in a group for which <expr> evaluates to something that IS NOT NULL

This distinction can be quite useful. Most of the time, we’ll simply COUNT(*) for convenience, but there are (at least) two cases where we don’t want that, for example:

When outer joining

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Entity Framework 6.3 and .NET Core 3 Support

.NET Core 3 .NET Core was presented by Microsoft in 2016, but its 1.x versions had limited set of features comparing to Full .NET Framework. Since then .NET Core has been drastically improved. .NET Core 2.0 has a significant part of Full .NET Framework features and includes new functionality and significant performance optimizations. This year, […]

How to limit the SQL query result set to Top-N rows only

Introduction In this article, we are going to see how we can limit the SQL query result set to the Top-N rows only. Limiting the SQL result set is very important when the underlying query could end up fetching a very large number of records, which can have a significant impact on application performance. Why limit the number of rows of a SQL query? Fetching more data than necessary is the number one cause of data access performance issues. When a given business use case is developed, the amount of data available... Read More

The post How to limit the SQL query result set to Top-N rows only appeared first on Vlad Mihalcea.

SQL ORDER BY RANDOM

Introduction In this article, we are going to see how we can sort an SQL query result set using an ORDER BY clause that takes a RANDOM function provided by a database-specific function. This is a very handy trick, especially when you want to shuffle a given result set. Note that sorting a large result set using a RANDOM function might turn out to be very slow, so make sure you do that on small result sets. If you have to shuffle a large result set and limit it afterward, then it’s... Read More

The post SQL ORDER BY RANDOM appeared first on Vlad Mihalcea.

2019 Open Source Database Report: Top Databases, Public Cloud vs. On-Premise, Polyglot Persistence

Ready to transition from a commercial database to open source, and want to know which databases are most popular in 2019? Wondering whether an on-premise vs. public cloud vs. hybrid cloud infrastructure is best for your database strategy? Or, considering adding a new database to your application and want to see which combinations are most popular? We found all the answers you need at the Percona Live event last month, and broke down the insights into the following free trends reports:

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Getting started with the MySQL Operator for Kubernetes

Kubernetes Operators are amazing and they are already playing an important role for those who are managing large scale applications. I personally think that we will manage all applications using Operators.

In this tutorial I will show you how to setup a MySQL cluster using the MySQL Operator on Kubernetes.

Prerequisites:

  1. Install kubectl
  2. Install Helm
  3. Kubernetes Cluster: Use minikube locally or check out Luca’s post on how to set up OKE.

Let’s start with cloning the MySQL repository which contains the …

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On the Database Market. Interview with Merv Adrian

“Anyone who expects to have some of their work in the cloud (e.g. just about everyone) will want to consider the offerings of the cloud platform provider in any shortlist they put together for new projects. These vendors have the resources to challenge anyone already in the market.”– Merv Adrian.

I have interviewed Merv Adrian, Research VP, Data & Analytics at Gartner. We talked about the the database market, the Cloud and the 2018 Gartner Magic Quadrant for Operational Database Management Systems.

RVZ

Q1. Looking Back at 2018, how has the database market changed?

Merv Adrian: At a high level, much is similar to the prior year. The DBMS market returned to double digit growth in 2017 (12.7% year over year in Gartner’s estimate) to $38.8 …

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