VPS hosting is very slow. What's the bottleneck?

Question

I've setup a new VPS hosting, to run a Drupal website but it is extremely slow.

It is Ubuntu 10, Apache, php5.2

I've enabled Multi-Processing Module (MPM) module and configured it as follows:

StartServers 4 MinSpareServers 2 MaxSpareServers 10 ServerLimit 20 MaxClients 20 MaxRequestsPerChild 200

But it is still too slow... it is a VPS slice: RAM 256MB BW 150GB

what could be the reason ? thanks

Update (Swaps)

             total       used       free     shared    buffers     cached
Mem:           245        220         24          0          1         26
-/+ buffers/cache:        192         52
Swap:          511        110        401

Solution 1

Make certain you are not regularly accessing swap space for anything - disk I/O is a very common bottleneck, particularly on Xen VPS' with relatively small RAM allocations (assuming you're at Slicehost, given your mention of using a "slice").

While having swap space seems like a plus (particularly because your VPS doesn't sputter and die when you try to run multiple memory-hungry applications like Apache w/dynamic PHP content and MySQL) it will quickly lead to substandard performance, particularly if you're on a VPS host node full of others doing the same thing.

Edit: I would highly recommend the LowEndBox Wiki (LowEndBox focuses upon virtual environments with memory allocations in the same neighborhood as your own) for optimization tips to get Apache and MySQL running smoothly within your virtual environment.

Solution 2

It's almost definitely not an Apache configuration issue, but you need to profile your application to find out where its time is being spent instead of blindly guessing at what the problem is. Xdebug is a popular tool for PHP profiling, and turning on the MySQL slow query log may help if MySQL is running inside your VPS.

Part of the problem with VPS environments is that since your VM doesn't really know what it's getting in terms of resources, it's practically impossible to determine if your server hardware is heavily oversubscribed. That makes things trickier.

Solution 3

First try the standard mpm settings:

<IfModule mpm_prefork_module>
    StartServers          5
    MinSpareServers       5
    MaxSpareServers      10
    MaxClients          150
    MaxRequestsPerChild   0
</IfModule>

Maybe you should also have a look at this: http://articles.slicehost.com/2010/5/20/configuring-the-apache-mpm-on-debian You should also reduce the KeepAlive settings.

What about the RAM? Are you sure you have enough and the server is not swapping? (free -m)

You should also check your database, it's relative easy with the Tuning Primer script: http://www.day32.com/MySQL/

Btw. on a Server with just 256MB RAM i would advise you to use a other Webserver like Lighttpd or Nginx (with PHP-FPM).

Comments

[SiXoS]

Start controlling database layer, and make sure you run a php byte code cacher like xcache

[aneuryzm]

I've installed mysql (it is local). Very simple installation as I always did before on other VPS.

[aneuryzm]

uhm ok thanks. But the point is that I've just setup the VPS, installed everything.. so there is not a lot to investigate. What could be the reason of php running slow.. or maybe Drupal running slow on a server ?

[aneuryzm]

@danlefree How do I check if the swap memory is used ?

[aneuryzm]

I've changed the values, but it is still the same. The server is fast if I visit a html page. It is a php/mysql problem I guess

[aneuryzm]

I've run the script you suggested but this is what I get - INITIAL LOGIN ATTEMPT FAILED -

[zaub3r3r]

You have to set your login variables first in ~/.my.cnf

[jgoldschrafe]

Code isn't magic, it does things. The entire point is to figure out where it's running slow so you can figure out why it's running slow. As you said, you have absolutely nothing else to go on.

[danlefree]

@Patrick - Run free -m

[aneuryzm]

@danlefree I've updated my question with the results. How should I interpret the numbers ? thanks

[danlefree]

@Patrick - It appears as though swap space is being allocated, though it may be held without being used. Run vmstat -a 1 and watch the si and so values while you request a page on your site to see how heavily swap is being relied upon (si and so will remain at 0 if your server is not actively using swap).

[aneuryzm]

@danlefree So, they are usually 0, but when I visit a page they both change (i.e. 0 0, 312 0, 324 1516, 36 6768, 0 0). So I guess the server is using swap.

[danlefree]

@Patrick - Yes, I would say that your server is relying upon swap to serve pages. Given that, your bottleneck is most likely disk I/O for all of those swap operations. Disk I/O on a shared server is an onerous bottleneck - do everything you can to avoid it.

[aneuryzm]

@danlefree uhm, What do you mean with "disk I/O". Are you talking low level, about number accesses to memory disk ? Or is it something else on VPS ?

[aneuryzm]

Anyway, I'm running exactly the same Drupal application on another VPS with the same RAM (256M) and it is not slow... (and I have more than 1 website there)

[danlefree]

@Patrick - By "disk I/O" I'm referring to low-level random access reading and writing (which involves a great deal of seek time per operation). Disk contention is a well-documented problem for low-end virtual private servers; swap space makes it worse. Related reading: etbe.coker.com.au/2008/08/27/…

[aneuryzm]

@danlefree I've just checked the swap on the other VPS hosting and the values are much lower (max 300).. I guess something in the configuration is different because the RAM is the same.

[zaub3r3r]

As you can see your Server is swapping, try to disable Apache modules which you don't need. However i think that 256MB RAM are not enough to run a well performing LAMP-setup. Databases need cache and Apache also isn't a saveaholic. You should think about switching to Lighttpd, it's easy to setup and works well with less RAM. You don't need to worry about the rewrite-stuff, there are enough examples on the internet. I can't tell you why the same setup works on a other VPS, maybe different virtualisation or other hardware (faster harddrives ;) )

[danlefree]

@Patrick - Anything that keeps your server from fighting other domU's for swap space will help :)

[aneuryzm]

@danlefree The difficulty is to find out how to not swap.

[danlefree]

@Patrick - Take a look over the articles under "Software Optimization Guide" at the LowEndBox Wiki for starters.

[aneuryzm]

@danlefree yeah thanks, I saw it before, but the link seems to not exist lowendbox.com/wiki/setup-base-debian-ubuntu-vps

[danlefree]

@Patrick - That guide can be found here: lowendbox.com/blog/… (though it involves using a different webserver)