Month: January 2010

Installing the Pandora One client on 64-bit Ubuntu 9.10

I was surprised and happy to see that the Pandora One client should work on Linux. It uses the Adobe Air framework which means that Pandora doesn’t have to write a specific Linux variant.

However, installing it on a modern 64-Bit Ubuntu 9.10 install took just a bit of manipulation to get it to work. Pandora provides some basic instructions for Linux users here, even though Linux is officially unsupported. Those instructions, along with the Adobe AIR notes here provided enough information for me to get it installed and working.

Here’s what I did:

  • Start out at the Pandora One site
  • Click on the "Download Pandora Desktop" link and save that file to /tmp
  • Follow the link to Install Adobe Air and save that file to /tmp also
  • Open a shell, and chmod the Adobe Air installer to 755 and then run it.
  • Go through the Adobe AIR install until it completes
  • Once Adobe AIR is installed, you will need to put some 32-bit libraries in place to make it run correctly. Some of the steps on Adobe’s site work, and some don’t, so this is what I did
  • Download the two .deb files for libnss3 and Libnspr4 to /tmp
  • From your shell, run: 
     sudo file-roller ./libnss3-1d_3.12.0~beta3-0ubuntu1_i386.deb
  • Navigate to data.tar.gz => /usr => lib. Click on all of the files in that directory and click Extract. Type in /usr/lib32/ so that they extract there, then close all of the file-roller windows.
  • Do the same thing with the libnspr4 .deb file that you downloaded
  • Copy the adobe cert store into place with this command: 
     sudo cp /usr/lib/libadobecertstore.so /usr/lib32
  • Now you can finally install the Pandora application by running: 
    sudo Adobe\ AIR\ Application\ Installer /tmp/pandora_2_0_2.air

    That should install the application correctly. It will add an icon to Applications / Accessories.

  • Upon starting up the Pandora One client, it currently complains about connecting to an untrusted server for me. I have to click to accept for this session each time

Now you should be able to play your Pandora music from your 64-bit Ubuntu 9.10 box.

Speed up a Linux Software Raid Rebuild

I’m setting up software raid on a running server and it is taking forever for the initial sync of the raid drives on the 1TB hard disks. It has been running for about 6 hours and says that it will take about 5 days (7400 minutes) as this pace:

[root@host ~]# cat /proc/mdstat
md1 : active raid1 sdb3[1] sda3[2]
      974559040 blocks [2/1] [_U]
      [>....................]  recovery =  3.9% (38109184/974559040) finish=7399.1min speed=2108K/sec

I did some read and write tests directly to the drives using dd to make sure that they were working okay, and they can operate at about 100 MB/s

[root@host ~]# dd if=/dev/zero of=/dev/sda2 bs=1024 count=1024000
    1048576000 bytes (1.0 GB) copied, 10.8882 seconds, 96.3 MB/s
[root@host ~]# dd if=/dev/zero of=/dev/sdb2 bs=1024 count=1024000
    1048576000 bytes (1.0 GB) copied, 11.1162 seconds, 94.3 MB/s
[root@host ~]# dd if=/dev/sda2 of=/dev/null bs=1024 count=1024000
    1048576000 bytes (1.0 GB) copied, 10.2829 seconds, 102 MB/s
[root@host ~]# dd if=/dev/sdb2 of=/dev/null bs=1024 count=1024000
    1048576000 bytes (1.0 GB) copied, 10.5109 seconds, 99.8 MB/s

What I failed to realize is that there is a configurable limit for the min and max speed of the rebuild. Those parameters are configured in /proc/sys/dev/raid/speed_limit_min and /proc/sys/dev/raid/speed_limit_max. They default to a pretty slow 1MB/s minimum which was causing it to take forever.

Increasing the maximum limit didn’t automatically make it faster either. I had to increase the minimum limit to get it to jump up to a respectable speed.

[root@host ~]# echo 100000 > /proc/sys/dev/raid/speed_limit_min 

[root@host ~]# watch cat /proc/mdstat
Every 2.0s: cat /proc/mdstat 
md1 : active raid1 sdb3[1] sda3[2]
      974559040 blocks [2/1] [_U]
      [=>...................]  recovery =  7.7% (75695808/974559040) finish=170.5min speed=87854K/sec

Now it is up around 87 MB/s and will take just a few hours to complete the rest of the drive.

PHP Wrapper Class for a Read-only database

This is a pretty special case of a database wrapper class where I wanted to discard any updates to the database, but want SELECT queries to run against an alternative read-only database. In this instance, I have a planned outage of a primary database server, but would like the public-facing websites and web services to remain as accessible as possible.

I wrote this quick database wrapper class that will pass all SELECT queries on to a local replica of the database, and silently discard any updates. On this site almost all of the functionality still works, but it obviously isn’t saving and new information while the primary database is unavailable.

Here is my class. This is intended as a wrapper to an ADOdb class, but it is generic enough that I think it would work for many other database abstraction functions as well as seamless data pump.

class db_unavailable {
    var $readonly_db;

    function __construct($readonly_db)
    {
        $this->query_db = $readonly_db;
    }

    function query($sql)
    {
        $args = func_get_args();
        if (preg_match("#(INSERT INTO|REPLACE INTO|UPDATE|DELETE)#i", $args[0])) {
            // echo "Unable to do insert/replace/update/delete query: $sql\n";
            return true;
        } else {
            return call_user_func_array(array($this->readonly_db, 'query'), $args);
        }
    }

    function __call($function, $args)
    {
        return call_user_func_array(array($this->readonly_db, $function), $args);
    }
}

I simply create my $query_db object that points to the read-only database. Then create my main $db object as a new db_unavailable() object. Any select queries against $db will behave as they normally do, and data-modifying queries will be silently discarded.