Rails initial request slow with mod_rails

Following up on my previous post , I’ve been experience slow load times (10-15 secs) on the initial request after application restarts. This has to do with the way mod_rails manages application instances (Although, I experienced this when using mongrel_cluster and proxy balancers). It will spin up instances on page request and each instance has an idle timeout. This just means after the timeout expires, mod_rails will shutdown that instance to conserve memory allocation. While you can change timeout value (see PassengerPoolIdleTime), this will only cause all instances that get spin up to live longer. After high load times, these instances will stick around longer than neccessary.

For low traffic sites (like mine), this idle timeout may be reached causing the next visitor to our website to experience a really long delay before page load. What we really want is an option to set a minimum number of instances. This would allow us to automatically spin up an instance during start up and keep it around. Unfortunately at this time, it doesn’t look like there is a way to set this.

As a workaround, I’ve setup a crontab that makes a request to my application every 5 minutes to prevent mod_rails from killing off all application instances.

To do this just run:

crontab -e

And then specific the following cron

*/5 * * * * wget -O /dev/null http://www.myapp.com 2>/dev/null

You can verify this is working correctly but just tailing your application logs and verify every 5 minutes you get a request.

You can also run

 passenger-status

You should see at least the count variable to be at least 1 instance.

Note, this workaround will not immediate start up an instance upon restart. You can add an initial request as part of your post deploy capistrano task though. You probably should be making sure your application is up after deploying or restarting the application anyways.

Rails initial request slow with mod_rails

Where is my sequel sock?

I was looking for where mysql.sock was since running rake db:bootstrap was complaining with “No such file or directory – /tmp/mysql.sock”. Rails looks for the mysql.sock file under /tmp/mysql.sock by default. Ubuntu using an apt-get install of mysql puts the mysql.sock file at /var/run/mysqld/mysqld.sock.

I always forget where it is. So, I’m writing it down.

/var/run/mysqld/mysqld.sock

You can also grep for it from mysql like so

>>  mysql -? | grep mysqld.sock
socket                            /var/run/mysqld/mysqld.sock
Where is my sequel sock?

Ubuntu upgrade broke WordPress

Something with my past two Ubuntu upgrades broke all the internal links on my blog running on WordPress.

It turns out the upgrade process changed the name of the target link on the .htaccess symbolic link file under my WordPress install directory.

After the install this is what was linked:

.htaccess -> /etc/wordpress/htaccess

Notice the missing “.” in .htaccess.

To fix it, I had to update the link to with

 >> ln -sf /etc/wordpress/.htaccess .htaccess

All the links work again!

Ubuntu upgrade broke WordPress

Top 8 Unix Commands for the Developer

As a developer, there are certain UNIX commands you find yourself typing repeatedly. Whether it’s to debug a production issue or just modifying some files, these commands have helped me do my job time and time again. Here’s my top 8:

  1. grep – Prints the lines that match the pattern provided in the files specified
    • Usage: grep <options> <pattern> <files>
    • Example: grep -n Exception production.log
      • Prints all the line (showing line numbers) in the file production.log that contain the string ‘Exception’
  2. tail – Only interested in a the last couple of lines in a file? tail allows you to quickly view the end of the file
    • Usage: tail <options> <file>
    • Example: tail -fn100 production.log
      • Shows the last 100 lines of the log and waits to display any new text appended to the file
  3. ssh – Log into remote servers
    • Usage: ssh -p<port> <username>@<hostname>
    • Example: ssh -p1234 [email protected]
      • Logs into the server named production on port 1234
  4. scp – Copies files to/from remote servers
    • Usage: scp -P<port> <source> <target>
    • Example: scp -P1234 /home/theo/myfile.txt [email protected]/home/jsmith
      • Copies myfile.txt from /home/theo to the server named production under /home/jsmith
  5. rm – Deletes stuff!
    • Usage: rm <options> <file>
    • Example: rm -rf mydir
      • Removes the entire directory and files with no prompt for confirmation (Use with caution!)
  6. ps – Shows process status
    • Usage: ps <options>
    • Example: ps aux
      • Displays the process status of processes for all users including those that are controlled by a terminal (system processes) sorted by CPU usage
  7. top – Similar to ps but it periodically updates the information such as CPU and memory usage
    • Usage: top
    • Example: top (duh!)
  8. kill – terminates a process
    • Usage: kill <option> <pid>
    • Example: kill -9 12345
      • Terminates the process with id of 12345 using a non-catchable, non-ignorable signal (that just means you REALLY mean to kill it)

I use lots of these commands in combination. For example, if tomcat seems to hang and won’t properly shut down I would do the following:

  >> ps aux | grep tomcat

I would then take the pid of tomcat and run:

  >> kill -9 <tomcat-pid>

Now you may be wondering why the “Top 8”, why not “Top 10”. Well, because 8 is the new 10 and those are all UNIX commands I know :).

What are some of the commands that you use to get through the day?

Top 8 Unix Commands for the Developer