Category Archives: Linux

All things Linux.

NPR developer talk at O’Reilly MySQL Conference and Expo 2010

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Joanne Garlow one of the Senior developers here at NPR , will be giving a talk this Tuesday at the 2010 O’Reilly MySQL Conference and Expo in Santa Clara, CA.  The talk is entitled ‘Migration from Oracle to Mysql : An NPR Case Study’ and will focus on some of the ‘lessons learned’ during our recent Oracle to Mysql migration, it will also cover some of the tools that we found useful during the migration as well as some of the issues we encountered concerning character encoding and concurrency.

If you are thinking about converting your backend databases from Oracle to Mysql and you are attending this conference, you should attend this talk, as I am sure it will be very informative and quite helpful to you going forward.


Mysql slow log parsing with Maatkit

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One of the tools that is included with Maatkit is called ‘mk-query-digest’.  If you have Mysql slow logging enabled, this perl script can me used to examine these entries, and provide a very useful and user friendly report that will help you understand the queries that are exceeding your current slow log threshold. You can then take the results and determine whether or not you have opportunity to do some schema and/or query optimization.

In order to get the ball rolling all you need to do is execute the following command:

‘perl /path/to/mk-query-digest /path/to/slow.log’

Once you do you will be presented with a report similar to the following:

# 200ms user time, 10ms system time, 9.59M rss, 11.17M vsz
# Overall: 199 total, 8 unique, 0.92 QPS, 3.44x concurrency ______________
#                    total     min     max     avg     95%  stddev  median
# Exec time           745s      1s     15s      4s      9s      3s      3s
# Lock time            4ms       0   159us    21us    66us    18us    16us
# Rows sent         16.35M       0 381.59k  84.16k 298.06k  81.83k  76.03k
# Rows exam         16.35M       0 381.59k  84.16k 298.06k  81.83k  76.03k
# Time range        2010-03-04 18:32:44 to 2010-03-04 18:36:21
# bytes             55.53k       6   7.67k  285.75  313.99  519.23  271.23

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Modifying ethernet interface order in Debian

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Sometimes after a fresh Debian Etch install  (I am not sure if this is fixed yet in Lenny or not), the order of your ethernet interfaces will be incorrect. You may also be in a position where you have more then two NIC cards and and you wish to swap eth0 and eth1 with eth2 and eth3, for consistency purposes for example.

In order to do so, you’ll need to make a change to the udev configuration file which controls which interfaces receive which names. You need to edit the following file:

‘/etc/udev/rules.d/z25_persistent-net.rules’

Simply make sure that you match the proposed interface with the correct MAC address and you are all set.

Go ahead and restart the server and you should be all set with the correctly labeled interfaces.

Subnet scanning with Nmap

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If you are ever wondering which ip addresses on your network are currently being used, you can use nmap to find out.

For example to scan an entire class C subnet you can use the following command:

‘nmap -v -sP 192.168.1.0/24 |grep up’

This will produce a list of ip addresses which are currently being used.

You can also use this command to find a list of inactive ip addresses when you are looking to add devices to your network:

‘nmap -v -sP 192.168.1.0/24 |grep down’

Introduction to Maatkit

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Maatkit is a group of perl scripts that provide advanced methods of administration for Mysql.

Here are a few of the more useful things that Maatkit allows you do to:

  1. Monitor MySQL replication delay
  2. Make a MySQL slave server lag behind its master.
  3. Ensuring slaves have the same data as masters
  4. Find duplicate indexes and foreign keys on MySQL tables.
  5. Execute SQL statements and print statistics.
  6. Execute queries on multiple servers and check for differences.

Here is the link to the Maatkit website which provides more details on each of the scripts.  I will be providing some real world examples of Maatkit usage in another post.

Percona patches for mysql 5.1

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Percona has recently released some of their performance patches for Mysql 5.1.  Previous to these patches were only available for the 5.0.x codebase.

You can read more about it here. The link also provides from interesting benchmarks as well, pitting these patches vs the standard storage engine setup.

To be clear, these patches work against the built in version of Innodb with comes standard with the Mysql server.

You can xtradb if you wish to use some of the Percona patches that pertain to the Innodb plugin that is offered by Innobase

Streming media server

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If you are looking for a way to stream media to either your xbox360 or your ps3 from a linux machine, then I highly recommend that you have a look at this project.  Ps3 Media Server is a java app that you can use to stream all kinds of content to either device.

I have been using it for almost a year now on Ubuntu and it has proven to be  extremely stable.

It also offers ‘on the fly’ transcoding which will allow you to play audio and video formats that might not be natively supported.

Here is the most well documented configuration guide I have come across while looking for tips and tricks.

Poor LSI SAS1068E Write Performance with Linux

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While doing research into poor write performance with Oracle I discovered that the server was using the LSI SAS1068E. We had a RAID1 setup with 300GB 10K RPM SAS drives. Google provided some possible insight into why we the write performance was so bad(1 2). The main problem with this card is that there is no  battery backed write cache. This means that the write-cache is disabled by default. I was able to turn on the write cache using the LSI utility.

This change however did not seem to any difference on performance.  At this point I came to the conclusion that the card itself is the blame.  I believe  that this is an inexpensive RAID card that is good for general use of RAID0 and Raid1, however for anything were write throughput is important, it might be better the spring for a something a little bit more expensive.

When it was all said and done we ended up replacing all the these LSI cards with Dell Perc 6i cards.  These cards did come battery backed…which allowed us to then enable the write cache, needless to say the performance improved significantly.

Poor Write Performance with Oracle

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We recently deployed an Oracle virtual machine for development and testing purposes. Imports and database migration scripts were taking several hours on existing VM’s, so we hoped this new machine with more RAM (32 GB) and more CPU horsepower (quad core Intel Xeon’s) would allow for those operations to move along much more quickly.

We soon got reports from users that this server was in fact much slower then the existing less powerful Oracle VM’s. After doing some poking around (with vztop) we discovered that there were no issues with cpu or memory resources, however the server was performing terribly when it came to I/O.

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