General help

Hi Mas,

Ah yes. We toyed with the ApacheLounge build last summer, but were hampered by the limited availability of FreeTDS on PHP 5.2.x; at the time of installation PHP 5.1.x on Apache's build was considered the most 'stable' setup. Now that moodle.org has it's own version of FreeTDS, it might be time to revisit things. (Although PECL4Win, which hosts many PHP caches, is currently down for maintenance.)

When I get more time in the coming weeks I'll look at benchmarking the various flavours of Apache, PHP, etc.

If it helps, our next step, once we've ruled out the Windows platform, is to move the front-end to a Linux box. The only 'must' in our spec is that the DB runs on MSSQL.

Best,
Ben

Hi Lewis,

Spec is very similar to yours. 2GHz, Quad Core, 4GB. Although our main box is shared with QuestionMark Perception, so resources are limited.

Dev box is 2GHz, Eight Core, 12GB; but this is running SQL Server as well.

Thanks,
Ben

Hi Lee,

We've not overcome it yet, but we are seriously looking at alternatives.

To summarise, our Moodle installation would be fine with high use, having 25-50 concurrent users online for 7+ hours is not an issue for our current installation. However, if the concurrent user count goes over 50 users, and towards 75 users, we start to see serious degradation in performance; pages time out, CPU usage spikes to 100% and remains there (on all cores), and eventually Apache gives up and restarts.

To recap, our server is setup as:
Moodle 1.9.4+
PHP 5.1.6 running as SAPI module under Apache 2.0.63 on Windows 2003
PHP also runs the APC cache.
MS SQL Server 2005, via FreeTDS driver (Kroman build)

Database and Web Server reside on different boxes, both Dual-Core 2.0GHz+ 4GB RAM+ boxes.



Testing methodology was twofold, firstly using a JMeter script to emulate 'real world' Moodle usage, and secondly a simply page to repeat and time a fairly complex query directly against the Moodle database (a simple 20-line script).

What we see is:

1. Using php_mssql is fine, no CPU spikes, and all queries return in a timely manner. You can load-test to your heart's content and the server rarely crashes or fails to return a page. Only problem is, that we can't use this driver due to the UTF-8/UCS-2 issue relating to it.
   
   
2. Using php_dblib (FreeTDS), things start to differ. The first few dozen queries are fine, but the web server soon gets overwhelmed if you place sufficient load on it.
   We've narrowed this down to FreeTDS' single-query nature (http://www.freetds.org/faq.html#pending), and PHP's habit of reusing connections (http://lists.ibiblio.org/pipermail/freetds/2003q3/013915.html). Both lead to a single query being processed at any one time, and so high-loads cause a backup to appear. Running SQL Profiler, you can actually see that the page loads (and queries) are run in turn, not concurrently.
   This is, of course, our interpretation of what is going on - others are welcome to comment.
   
   
3. We've also confirmed this by using a MySQL backend, and running the same tests. You get performance on-par with using the native php_mssql driver, both of which are ten-times the performance of the FreeTDS driver.

To us this seems to localise it to the FreeTDS driver and nothing else. Both the Kroman build and the Moodle build are affected by this, as they both rely on a single query-per-connection.


We're currently investigating other ways of handling our database connections:

• We're going to look at ODBTP in the coming weels, but we've no hope that it'll improve things (we ruled it out when we intially installed Moodle two years ago).
• We're going to see what Moodle 2.0 offers. The Moodle team appear to be working on Microsoft's new php_sqlsrv native driver, which might improve performance.
• We're investigating load-balancing our setup.
• Finally, we're looking at moving our database back-end to MySQL.

So yeah, that's where we're at. It'd be interesting to see if anyone else can confirm this FreeTDS behaviour (if only to prove that I'm not going mad).

Best,
Ben