[Opensim-dev] Update for group module & flotsam

[Kevin Cozens]

On 12-10-03 12:00 PM, Michelle Argus wrote:
> - added agents online status to flotsam
> - added agents last login data to flotsam
> - displaying the online/last login data in the groupmembers list viewerside
> - added optional filter to get a memberlist of online members only instead
> of allways receiving all groupmembers
> - send groupchat IMs only to online members.
>
> The changes can be found in the 2 gits here: https://github.com/MAReantals

Nice to see some missing functionality added. Sending group messages to 
avatars that are not on line was clearly a bug that needed fixing.

The proposed changes started me thinking about the groups code and wondering 
if there were other areas of the code that could be written differently to 
minimize chat lag. What I have seen so far makes me realize there are a 
number of ways the overall groups code can be improved. I'll start with some 
comments about online status in groups before I get to the main areas where 
improvements can be made.

Having an online status in the groups database raises the question as to 
whether it might get out of sync with an avatars real online status but this 
may not be much of a problem. A status of online could be forced when an 
avatar opens a group chat window. Offline status could be set on a failure 
to send a group chat message fails (and determines user is offline?).

The updated group code adds OnClientClosed handler to check and update an 
avatars online status. Does OnClientClosed get called on TP to a different 
region or on sim boundary crossings? If it is called at times other than 
during login/logout it should check if the avatars status has changed before 
issuing the database update call as that is an "expensive" call involving an 
external web server to update the group database.

The preceeding items are minor issues. Now for the bigger issues.

I was surprised (almost shocked) to find that a call is made to 
GetGroupMembers() for *every* chat message that is to be sent. [It is also 
called when sending group notices.]

If that doesn't sound bad enough it gets worse when you realize what is 
involved. The C# code invokes a PHP script on a webserver to query a 
database to get the list of members. The PHP code uses a complex SQL query 
that contains 3 JOIN's and one LEFT JOIN. To top it all off, once it has the 
list of members the PHP code then runs another query to get group 
permissions for each member.

The SQL query with the JOIN's makes one question the design of the group 
database tables. I think it is more likely that it is trying to return more 
data than is required when determining which avatars should receive a group 
chat message or notice.

I think the first thing to do is create a new function to get online group 
members that returns the minimum amount of data required to send chat and 
notices. I don't think that should involve more than two tables versus the 
three currently used. It could be done with one but the second table is 
needed to see if the member is online. If there is a simpler/faster way for 
the group .cs code to check if a user is online given an avatar UUID that 
doesn't require an external database check that would be better. The online 
status wouldn't be needed in the groups database, the list of members could 
be filtered in the .cs code so only online members get chat/notices.

The next(?) step would be to do the SQL queries from inside the C# code and 
eliminate the need for the use of a webserver and the PHP code.

A more complex solution to reducing overhead and lag in group chat is to set 
up a cache to hold the online group member data to avoid multiple requests 
to an external webserver on each message.

The other question to be asked is if the group code is in anyway threaded? 
Can it handle multiple chat messages at the same time or is it sequential 
and processing only one message at at time? Is the group module a bottle 
neck when people are chatting in several groups at the same time?

One last issue remains. How do we test changes to the group chat code? A 
test bed is needed to allow simulation of a large number of people chatting 
in several groups at the same time.

I have suggested working on the group module as a possible first project for 
the #metaversity people. It is self-contained enough to be a good first 
project as it doesn't need a lot of broad knowledge of the overall code 
base, not to mention the amount of "bang for the buck" as it is of benefit 
to anyone using group chat.

-- 
Cheers!

Kevin.

http://www.ve3syb.ca/           |"Nerds make the shiny things that distract
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