[xwiki-devs] [Idea] Implementing a Log console inside XE

Thomas Mortagne thomas.mortagne at xwiki.com
Fri Mar 18 09:17:57 UTC 2011

On Fri, Mar 18, 2011 at 10:10, Vincent Massol <vincent at massol.net> wrote:
> On Mar 18, 2011, at 10:01 AM, Thomas Mortagne wrote:
>> On Fri, Mar 18, 2011 at 09:46, Vincent Massol <vincent at massol.net> wrote:
>>> I'm stupid, there's no need to relate it to the AS. The AS can simply ignore those events and we can have a separate listener to receive them....
>> Yes can be a special tool for that.
>>> -Vincent
>>> On Mar 18, 2011, at 9:39 AM, Vincent Massol wrote:
>>>> Hi,
>>>> Right now logs go to a file on the filesystem. However this is not right since most logs are application logs and should be visible to wiki developers. For ex, if I use a deprecated API, I need to see it. It shouldn't go to admins only and shouldn't "pollute" the system logs.
>>>> Hence I believe we need a Log Console available somewhere (we could make it avail in the Admin UI FTM).
>>>> I'd like to discuss an implementation idea I've had this morning:
>>>> * Send application logs as Observation Events and make the available in the Activity Stream (AS)
>>>> Pros:
>>>> * Infrastructure already in place
>>>> * Fits the AS goal: temporary information and is purged regularly
>>>> * (Of course the Activity gadget would not display them)
>>>> * They can be sent remotely as remote events in the future; this allows implementing a remote console to monitor an XE or XEM from a distance
>>>> Cons:
>>>> * We need to assess the performance risk and more generally we need to make the AS scalable (I don't think it is now).
>>>> * 2 ideas for scaling up the Observation/AS:
>>>> 1) Have the Observation Manager save events to be notified into a Queue and have one or several separate threads take those events and send them to listeners. Right now if one listener takes time in its onEvent() method it slows down the whole chain since they are called serially. Note that if we want even better scalability, the Queue could be stored externally to XWiki (a JMS queue for ex) and scalability can be achieved by app server instances listening to this queue to process it.
>> IMO if a listener takes time in its onEvent() it can always do that
>> message queue itself, that's what Lucene plugin do for example.
> Yes i know but it's nice from an architecture POV to do it at this level rather than *hope* that all listeners (including those not coded by us) will be good citizens.
>> We
>> dono't absolutely need to implement that in Observation Manager. Also
>> you can't do that for all events since some of them are
>> question/answer events or event responsible for setting and unsetting
>> the contexte before and after a task for example.
>>>> 2) Have a way to tell the AS what storage to use for specific Event Types. For example the AS could use an in-memory storage for Log Events while using a DB storage for other events. This would be useful since I don't think we really need to store logs in the DB. Note that the cache could be indexed on the message so only one instance of each log message is preserved (no need for dups), possibly with a counter to mention how many of them there were (that's an optimization).
>>>> I believe 2) might be enough for performances in a first implementation of the log console.
>>>> WDYT?
>> Make the default org.xwiki.component.logging.Logger take care of
>> producing theses events so that it support already existing log and
>> makes it easier for a component than having to do that using
>> Observation Manager.
> Yes although I think I'd prefer to slowly move them to send events instead of logging and have the logging be done in the listener (ie turn the logic upside down).

If we want all the log to produce events that's the way to go IMO. 1)
it's a lot easier to use a logging API to log 2) you can be sure you
will have very few log events if you don't do it that way, people will
always forget to send log events since that's really not natural. I
don't think it's really turn the logic upside down, it make the Logger
API an helper that's all. If you have to create event called
"LogEvent" and not something unrelated directly to logging that is
transformed as log by a listener it's exactly the same logic.

> I'm not 100% sure though, needs some more thoughts.
>> +1 for the general idea
> Thanks
> -Vincent
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Thomas Mortagne

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