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Showing entries 1 to 16

Displaying posts with tag: Statistics (reset)

What the Mean Really Means
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When analyzing response time, or latency, you need much more information than an average provides. The average, commonly the arithmetic mean, shows the index of central tendency. But, as I found in earlier posts, the tendency is often not central, but may be skewed by outliers, or split by multiple modes. How often these factors occur was determined quantitatively, using tests and a survey of hundreds of production servers and different types of latency: over 95% had six-sigma outliers, and

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Modes and Modality
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It is a truth universally acknowledged that the average is the index of central tendency. But what if the tendency isn’t central?

I’ve worked many performance issues where the latency or response time was multimodal, and higher-latency modes turned out to be the cause of the problem. Their existence isn’t shown by the average – the arithmetic mean; it could only be seen by examining the distribution as a histogram, density plot, heat map, or frequency trail. Once you know that more than

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Fun with Bugs #14 - InnoDB in MySQL 5.6
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InnoDB improvements in MySQL 5.6 are well known. One of the key reasons to upgrade to MySQL 5.6 for most users is to get the benefits of improved performance, scalability, new monitoring features and fulltext indexes support in InnoDB.

Is there anything to double check before assuming that InnoDB in MySQL 5.6 is just better than any older version for any practical purposes? Let's review known public InnoDB-specific bug reports. Here is my "Top 10" list, as of MySQL 5.6.12, starting with most recent reports:

  • Bug #69424  - maybe I miss something (I am not the only one though), but I see no way to continue using raw devices (on Linux at least) to store InnoDB data. You had working raw device in 5.5.32, then you upgrade to 5.6.12 and just can not start MySQL any more.




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    Statistical functions in MySQL
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    Even in times of a growing market of specialized NoSQL databases, the relevance of traditional RDBMS doesn't decline. Especially when it comes to the calculation of aggregates based on complex data sets that can not be processed as a batch like Map&Reduce. MySQL is already bringing in a handful of aggregate functions that can be useful for a statistical analysis. The best known of this type are certainly:

    Read the rest »

    Persistent index statistics for InnoDB
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    In browsing the BZR tree for lp:mysql-server, I noticed some rather exciting code had been merged into the Innobase code.

    You may be aware that InnoDB will do some index dives when opening a table to get some statistics about the indexes that can help the optimiser make good query plans.

    The problem being that this is many disk seeks. It means that on server restart, you have to spend a whole bunch of time seeking around the disk reading index pages.

    Not any more.

    There is now code merged in to store the calculated statistics in a table inside InnoDB so that these index dives don’t have to happen on startup.

    Originally, this looked like it was going to make it into InnoDB+. The

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    Kontrollbase gets more environment statistics
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    More stats for your consumption! Here are the latest additions to the environment overview reporting features. On the overview page, as of revision 238, you will find the following data for your servers. Update your revision now using ’svn update’ to get the new features or wait until the next formal release if you are [...]
    OpenSQLCamp Videos online!
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    OpenSQLCamp was a huge success! I took videos of most of the sessions (we only had 3 video cameras, and 4 rooms, and 2 sessions were not recorded). Unfortunately, I was busy doing administrative stuff for opensqlcamp for the opening keynote and first 15 minutes of the session organizing, and when I got to the planning board, it was already full….so I was not able to give a session.

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    OpenSQLCamp Lightning Talk Videos
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    OpenSQLCamp was a huge success! Not many folks have blogged about what they learned there….if you missed it, all is not lost. We did take videos of most of the sessions (we only had 3 video cameras, and 4 rooms, and 2 sessions were not recorded).

    All the videos have been processed, and I am working on uploading them to YouTube and filling in details for the video descriptions. Not all the videos are up right now….right now all the lightning talks are up.


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    Four short links: 14 August 2009
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  • Page2Pub -- harvest wiki content and turn it into EPub and PDF. See also Sony dropping its proprietary format and moving to EPub. Open standards rock. (via oreillylabs on Twitter)
  • SQL Pie Chart -- an ASCII pie chart, drawn by SQL code. Horrifying and yet inspiring. Compare to PostgreSQL code to produce ASCII Mandelbrot set. (via jdub on Twitter and Simon Willison)
  • How
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    Big Data: SSD's, R, and Linked Data Streams
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    The Solid State Storage Revolution: If you haven't seen it, I recommend you watch Andy Bechtolsheim's keynote at the recent Mysqlconf. We covered SSD's in our just published report on Big Data management technologies. Since then, we've gotten additional signals from our network of alpha geeks and our interest in them remains high.


    R and Linked Data Streams: I had a chance to visit with Dataspora founder and blogger Mike Driscoll, an enthusiastic advocate for the use of the open source statistical


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    MCDBA Certification – KPIs
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    A few interesting KPIs about certified people and their current location (the fact that many people travel from one country to the other for work is very popular these days especially in the IT sector): Before starting to read, I am hereby assuming the MySQL list of MCDBAs is on a residence basis not citizenship. There are [...]
    Drizzle Commit Statistics
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    Per day:

    Per Month:

    Or more interestingly… What day are commits being made? Are we working over the weekend?

    Do we work all night?

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    xtstat: Tells you exactly what PBXT is doing!
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    I have created a new tool, called xtstat, for analyzing the performance of the PBXT storage engine.

    The way it works is simple. PBXT now counts all kinds of things: transactions committed and rolled back, statements executed, records read and written, tables and indexes scanned, bytes read, written and flushed to various types of files: record, index, data logs, transaction logs, and so on.

    A SELECT on the system table PBXT.STATISTICS (or INFORMATION_SCHEMA.PBXT_STATISTICS if PBXT was built inside the MySQL tree) returns the current totals of all these counters. xtstat does a SELECT every second on this table and prints the difference. In this way, you can see how much work PBXT is doing in each area.

    There are currently 48 different statistics:


    To ensure all








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    MyISAM Statistics Gathering
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    So, how does one gather statistics on indexes? With InnoDB it’s one thing, with MyISAM it’s another thing. This post however, will focus on MyISAM. There are various ways, each having their own drawbacks and positive sides.

    What about ANALYZE TABLE? It’s great — very fast in InnoDB. But with MyISAM a lock occurs while scanning the table.

    OPTIMIZE TABLE? Still relatively quick with MyISAM, unless the table in question is huge. InnoDB requires an ALTER TABLE — it might take forever, depending on the server configuration, as OPTIMIZE TABLE for InnoDB maps to a ALTER TABLE tableName ENGINE=InnoDB

    We all know how ANALYZE TABLE, REPAIR TABLE, and OPTIMIZE TABLE work with MyISAM. However, there’s a less explored way, for MyISAM

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    Interesting Internet Usage and Social Networking Statistics
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    Over the weekend I took some notes from a presentation and did some research from various sources. The result was a blog post about Internet trends that I posted on my personal blog. There are some very interesting statistics about Internet usage and social networking. Also, Facebook fans will find some interesting facts as well.
    Drupal's database interaction
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    Topic: DrupalDrupal performanceStatisticsMySQL

    I used XDebug to profile the behavior of Drupal, and to study the interaction with the database server. I aggregated the profile information of 100 requests to the main page using the "Apache, mod_php, PHP4, APC" configuration used for previous benchmark experiments. More information about my experimental setup is available at that page. XDebug generates a trace file with all the profile information which I visualized using

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    Showing entries 1 to 16

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