[Using Sakai] Who's online feature

[Charles Severance]

Elizabeth,

Sam's answer is quite right about the nature of what happens when things start to slow down.   And also he points out that we as a developer community want to reduce the performance impact of the presence feature but have not done so yet.

So until we change the software, I will go back to the point of my message - if using the current version of Sakai, your vendor is forcing you to permanently turn off presence with no plan as to when to turn it back on - that is a big red-flag for me that suggests they do not have enough hardware capacity allocated to your site to deal with your peak loads and instead of upgrading your server resources they are doing something that will only delay performance problems - not permanently fix them.

If on the other hand they have offered to upgrade your server hardware and for one reason or another the answer was "no", turning off presence is one (less-than-ideal) way to buy a little time without upgrading hardware.

/Chuck

On Aug 26, 2013, at 9:15 AM, Sam Ottenhoff <ottenhoff at longsight.com> wrote:

> Yes, exactly, the database is capable of a certain level of performance.  Once queries start piling up (waiting to be processed), the system begins to melt down as users furiously refresh, the database struggles, and users can no longer take assessments, grade assignments, or use Sakai.
> 
> Say if your database is capable of an arbitrary number of queries (ignoring that some queries are easy and some are difficult) like 300k queries per minute. Who's Online in pre-Sakai 2.9 is a simple polling mechanism that checks with the database on the number of users in a site every 5 seconds or so.  So if you have 5k users logged into Sakai, that equals 60k database queries per minute just for Who's Online.  So Who's Online is taking up a certain amount of your database's performance capacity that could potentially be really important during times of high demand (e.g., 200 users taking an online assessment at the same time).
> 
> Does the 2.9+ Jgroups code introduced for portal chat also replace the old database polling mechanism?  If yes, I would investigate this approach as it would be a way of doing presence without the constant volume of queries to the database (https://jira.sakaiproject.org/browse/SAK-22286).  
> 
> --Sam 

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