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Displaying posts with tag: mk-query-digest (reset)
Profiling your slow queries using pt-query-digest and some love from Percona Server

This guide will get you up and running with how to identify the bottleneck queries using the excellent tool pt-query-digest. You will learn how to use and analyze the output returned by pt-query-digest. You will also learn some differences between slow query logging in various MySQL versions. Later on in the post I will also show you how to make use of the extra diagnostic data available with Percona Server.

The post Profiling your slow queries using pt-query-digest and some love from Percona Server appeared first on ovais.tariq.

Book Review – Effective MySQL

Read the original article at Book Review – Effective MySQL

Effective MySQL: Optimizing SQL Statements by Ronald Bradford No Nonsense, Readable, Practical, and Compact I like that this book is small; 150 pages means you can carry it easily.  It’s also very no nonsense.  It does not dig too deeply into theory unless it directly relates to your day-to-day needs.  And those needs probably cluster [...]

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New algorithm for calculating 95 percentile

The 95 percentile for query response times is and old concept; Peter and Roland blogged about it in 2008. Since then, MySQL tools have calculated the 95 percentile by collecting all values, either exactly or approximately, and returning all_values[int(number_of_values * 0.95)] (that’s an extreme simplification). But recently I asked myself*: must we save all values? The answer is no. I created a new algorithm** for calculating the 95 percentile that is faster, more accurate, and saves only 100 values.***

Firstly, my basis of comparison is the 95 percentile algo used by …

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Drizzle 7 plugins

Last week I wrote about my experience compiling Drizzle 7 on Mac OS X 10.6. Then David Shrewsbury informed me of his nearly identical blog post: Installing Drizzle from source on OS X. Once Drizzle 7 was running on my box, I immediately looked to see what plugins where available because Drizzle uses a lot of plugins and they are one of its notable differences from MySQL. In my humble opinion, Drizzle’s plugins will primarily influence how database professionals evaluate and decide whether or not to use Drizzle because so many of Drizzle’s features are plugins. Therefore, let’s look briefly at some the plugins included with Drizzle 7.

The plugin directory of the Drizzle 7 tarball lists 79 plugins. Each plugin …

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mk-query-digest Tips – Showing all hosts & users

The Maatkit tools provide a suite of additional MySQL commands. There is one command I use constantly and that is mk-query-digest.

Unfortunately the documentation does leave a lot to be desired for usability. While throughout, it is a man page and not a user guide. Several of us have discussed writing better documentation however it’s always a matter of time. I have however learned a number of tips and I’d like to share them in smaller digests.

The first is showing additional display. Maatkit works on truncating per line output to a reasonable length of 73 characters?

One of those lines is the list of hosts that connected to MySQL for a query, for example.

# Hosts                  4 192.168.40... (2), 192.168.40... (2)... 2 more
# Hosts                  3 (12), …
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tcpdump errors on FreeBSD for mk-query-digest

While I use this tcpdump command for MySQL query analysis with mk-query-digest, I found recently that it didn’t work on FreeBSD

$ tcpdump -i bge0 port 3306 -s 65535 -x -n -q -tttt -c 5
tcpdump: syntax error

It left me perplexed and reading the man page seemed to indicate my options were valid. I tried a few variances just to be sure without success.

$ tcpdump -i bge0 -c 5 port 3306 -x
tcpdump: syntax error
$ tcpdump -i bge0 -c 5 port 3306 -q
tcpdump: syntax error
$ tcpdump -i bge0 -c 5 port 3306 -tttt
tcpdump: syntax error

The solution was actually quite simple in the end, it had nothing to do with the commands, it had everything to do with the order of them. Placing port as the last option solved the problem.

$ tcpdump -i bge0 -s 65535 -x -n -q -tttt -c 5  port 3306
$ uname -a
FreeBSD …
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Videos of Pythian Sessions from the 2010 O’Reilly MySQL Conference and Expo

Here’s a sneak peek at a video matrix — this is all the videos that include Pythian Group employees at the MySQL conference. I hope to have all the rest of the videos processed and uploaded within 24 hours, with a matrix similar to the one below (but of course with many more sessions).

Title Presenter Slides Video link
Details (Conf. site link)
Main Stage
Keynote: Under New Management: Next Steps for the Community Sheeri K. Cabral (Pythian) N/A 18:16
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OpenSQLCamp Videos online!

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.

Drizzle Client Rewrite – Clark Boylan leads the requirements and design discussion for rewriting the Drizzle Client Drizzle Plugin Hacking[Read more]
Debugging and ripple effects

Like I said earlier, every tiny change that the test suite reveals after code changes is significant. I caught a very subtle “bug” today in recent changes to mk-query-digest (a.k.a. mqd). If you like to read about subtle bugs, read on.

An mqd test on sample file slow023.txt began to differ after some pretty extensive code changes of late:

< # Query 1: 0 QPS, 0x concurrency, ID 0x8E38374648788E52 at byte 0 ________
> # Query 1: 0 QPS, 0x concurrency, ID 0x2CFD93750B99C734 at byte 0 ________

The ID which depends on the query’s fingerprint has changed. It’s very important that we don’t suddenly change these on users because these IDs are pivotal in trend analyses with mqd’s --review-history option. First some background info on the recent code changes and then the …

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Zero is a big number

I made changes to mk-query-digest yesterday that I didn’t expect to cause any adverse affects. On the contrary, several tests began to fail because a single new but harmless line began to appear in the expected output: “Databases 0″. Perhaps I’m preaching to the choir, as you are all fantastic, thorough and flawless programmers, but as for myself I’ve learned to never take a single failed test for granted.

One time a test failed because some values differed by a millisecond or two. Being curious I investigated and found that our standard deviation equation was just shy of perfect. I fixed it and spent hours cross-checking the myriad tiny values with my TI calculator. Probably no one cared about 0.023 vs. 0.022 but it’s the cultivation of a disposition towards perfection that matters.

My innocuous changes yesterday introduced a case of Perl auto-vivification. Doing:

my ($db_for_show) = $sample->{db} ? …

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