Application Speed?

[eluser]Eric Brown[/eluser]
I have an application written in CodeIgniter running on 2 web nodes and 1 db node on the cloud at VPS.net. The response time for all processing ranges between 60 and 80 ms for a single request. I need to get it down to 30 or 40.

When I do load testing the response time increases to 300 to 500ms and is steady around there. My node usage can jump up to 10 nodes on the web VPS while the db node seems unaffected which makes sense since it's just making writes to the db.

My question is, since the web node scales up automatically to 10 nodes to handle the heavy load, will buying the nodes so I am guaranteed their resources have any affect? What if I scale my VPS up to 60 nodes?

I can't tell if "throwing more hardware" at my app will have any affect or if it's simply going as fast as it can and I need to rewrite my app.

[eluser]Pascal Kriete[/eluser]
You'll need to start gathering a lot more statistics.

Figure out where the bottlenecks are, don't just blindly throw more tech at the problem.

- How many hits per day, hits per hour at peak?
- What is causing the slow down? The database or the frontend?
- Look at mysql's slow query log, does anything stand out?
- How much file system usage does your app create? Do you have a lot of uploads/downloads?
- What kind of PHP memory usage execution times are you seeing for page loads
- Do you have any caching in place?

Once you start to see where you're going wrong you can adjust as needed.

It sounds like you're hosting this yourself. Do you have someone who knows how to effectively configure mysql?

[eluser]Eric Brown[/eluser]
Thanks for the reply. Here's some more info in case it helps.

- How many hits per day, hits per hour at peak?

QPS under load is 24. Trying to plan for 100QPS
- What is causing the slow down? The database or the frontend?
The front-end, application logic is causing the spike in CPU usage. I don't know why yet.

- Look at mysql’s slow query log, does anything stand out?

I will look this. The thing is, I'm just doing Inserts with the only difference being what data is being inserted...I mean, it's just one table.

- How much file system usage does your app create? Do you have a lot of uploads/downloads?

Not sure what you mean by this. The table itself is about 2 million records right now and growing. About a gig of storage space.

- What kind of PHP memory usage execution times are you seeing for page loads

5 megs of memory is what the profiler says. Should I be looking somewhere else?

- Do you have any caching in place?
I have my lookups store in Memcache. Since I'm just writing to a db, there really isn't anything to cache. It's simply a web logging app that returns a 1x1 pixel.

[eluser]Eric Brown[/eluser]
It looks like I could benefit from worker MPM. Are there any library conflicts / issues that CodeIgniter would have?