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If your Linux server is bogged down by disk I/O, your first step may often be to use the top command in the terminal to check load averages.Continue reading...
A Debezium investigation: how MySQL synonyms INT and INTEGER were treated as different types.One of our CDC pipelines started failing with a ClassCastException on every batch.java.lang.ClassCastException: class java.lang.Integer cannot be cast to class java.lang.LongThe pipeline was producing an Integer, but the downstream consumer expected a Long. Every run failed in the same way, which pointed us toward a schema mismatch rather than an issue with individual records.Background: how CDC worksTo see why a mismatch like that can hide for years, it helps to know how CDC actually works. Most…
If you've ever looked at your server and wondered why it's using swap even though plenty of RAM is available, you're not alone. This is a common scenario on Linux systems, and it can impact performance if not addressed.Continue reading...
Introduction In this article, I’m going to show you how to optimize the queries executed by a Spring application running on MySQL using Releem. For a short introduction about Releem, check out this previous article, in which I explained how to set up Releem to collect metrics from your MySQL database. Spring Petclinic application The application under test is going to be the well-known Spring Petclinic that we are going to run using the MySQL profile: After starting the application, we are going to run the petclinic_test_plan.jmx JMeter test plan that is... Read More The post MySQL Query…
In a previous blog post, we’ve advertised the use of SQL EXISTS rather than COUNT(*) to check for existence of a value in SQL. I.e. to check if in the Sakila database, actors called WAHLBERG have played in any films, instead of: Do this: (Depending on your dialect you may require a FROM DUAL clause, … Continue reading An Efficient Way to Check for Existence of Multiple Values in SQL →
In MySQL, you cannot do this: The UPDATE statement will raise an error as follows: SQL Error [1093] [HY000]: You can’t specify target table ‘t’ for update in FROM clause People have considered this to be a bug in MySQL for ages, as most other RDBMS can do this without any issues, including MySQL clones: … Continue reading Workaround for MySQL’s “can’t specify target table for update in FROM clause” Error →