April 20, 2014

Testing Intel SSD 520

Following my previous benchmarks of SATA SSD cards I got Intel SSD 520 240GB into my hands. In this post I show the results of raw IO performance of this card.

The relationship between Innodb Log checkpointing and dirty Buffer pool pages

This is a time-honored topic, and there’s no shortage of articles on the topic on this blog. I wanted to write a post trying to condense and clarify those posts, as it has taken me a while to really understand this relationship. Some basic facts Most of us know that writing into Innodb updates buffer […]

Make your file system error resilient

One of the typical problems I see setting up ext2/3/4 file system is sticking to defaults when it comes to behavior on errors. By default these filesystems are configured to Continue when error (such as IO error or meta data inconsistency) is discovered which can continue spreading corruption. This manifests itself in a worst way […]

The two even more fundamental performance metrics

In a recent blog post, I wrote about four fundamental metrics for system performance analysis. These are throughput, residence time, “weighted time” (the sum of all residence times in the observation period — the terminology is mine for lack of a better name), and concurrency. I derived all of these metrics from two “even more […]

How to use tcpdump on very busy hosts

Often I run into problems when trying to use mk-query-digest with tcpdump on “very” busy hosts. You might be thinking, “very busy is a relative and unquantifiable term,” and you’d be right, so I’ll phrase this differently. Let me give a little background to the problem first. Mk-query-digest tries to handle dropped or missing packets […]

Different flavors of InnoDB flushing

In my recent benchmarks, such as this one about the Virident TachIon card, I used different values for innodb_buffer_pool_size, like 13GB, 52GB, and 144GB, for testing the tpcc-mysql database with size 100G. This was needed in order to test different memory/dataset size ratios. But why is it important, and how does it affect how InnoDB works […]

How well does your table fits in innodb buffer pool ?

Understanding how well your tables and indexes fit to buffer pool are often very helpful to understand why some queries are IO bound and others not – it may be because the tables and indexes they are accessing are not in cache, for example being washed away by other queries. MySQL Server does not provide […]

Introducing tcprstat, a TCP response time tool

Ignacio Nin and I (mostly Ignacio) have worked together to create tcprstat[1], a new tool that times TCP requests and prints out statistics on them. The output looks somewhat like vmstat or iostat, but we’ve chosen the statistics carefully so you can compute meaningful things about your TCP traffic. What is this good for? In […]

Color code your performance numbers

When analyzing how good or bad response time is it is not handy to look at the averages, min or max times – something what is easily computed using built in aggregate functions. We most likely would like to see some percentile numbers – 95 percentile or 99 percentile. The problem is computing these in […]

Tuning InnoDB Concurrency Tickets

InnoDB has an oft-unused parameter innodb_concurrency_tickets that seems widely misunderstood. From the docs: “The number of threads that can enter InnoDB concurrently is determined by the innodb_thread_concurrency variable. A thread is placed in a queue when it tries to enter InnoDB if the number of threads has already reached the concurrency limit. When a thread […]