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From Bernd Koecke>
Subject Re: Load balancing patch
Date Tue, 07 May 2002 15:49:17 GMT
Hi Mathias,

a looked at your patch and I think there are two bugs:

1) You set in_recovering of a woker which is in error_state to JK_TRUE even if
you don't select him for handling the request. This should be moved into the
next if clause when the worker is choosen.

2) When a local/main worker goes down and was set to error_state it would never
be asked again. Because if the local/main worker was in error and the time for a
new test has come you set rc only to this worker if it is no local worker and
this will never be true. And because of this and 1) in_recovering == JK_TRUE, so
it is dead for ever.

Thats why I have a more complicated if-statement in my patch. When I check if
the worker is in error state and this is true, I have to check if I can take it
anyway. Because I can't reach the else part of the if anymore.

My test environment is like in the explanation of my patch:

I got two nodes with one apache and tomcat on each node. So I have only one
local_worker per node and the mode is reject. When I shutdown tomcat I got an
error. But after starting up tomcat again it is still unreachable.


Mathias Herberts wrote:
> Here is  my patch to  the load balancing  code. I have tested  the jk1
> part but not the jk2. The behavior should be identical though.
> The concept of local worker is introduced. Local workers form a subset
> of the  balanced workers,  those workers handle  the requests  with no
> session information or requests with session info but whose worker has
> failed.
> The list of local workers is specified in the files
> as follows:
> Internally the  module will  rearrange the workers'  list so  that the
> local workers appear first in the list. For the example above the list
> will be rearranged as:
>      w4,w6,w3,w1,w5,w2
> When a request comes in it is  either part of a session or not. If the
> request  is part  of  a session  then  the worker  having created  the
> session is selected  (according to the session route  appearing in the
> session  id). If  this worker  has failed,  the request  is considered
> sessionless.   For requests without  a session,  the workers'  list is
> scanned from the beginning, selecting the worker not in error with the
> lowest  lb_value.   When  the   last  local  worker  is  reached,  two
> alternatives  exist  depending  on   the  value  of  the  fault_action
> property.   If fault_action  is set  to reject  then if  a  worker was
> selected it is  returned as the most suitable  worker for the request,
> if no  worker was selected  so far, meaning  all local workers  are in
> error, a null  value is returned as the  most suitable worker, meaning
> the  request is  in  error. If  fault_action  is set  to balance,  the
> selection processs continues.
> For jk1, if fault_action is set to balance, non local workers in error
> can be  selected to handle  the request. In  jk2 in error  workers are
> never selected.
> The fault_action is specified as follows:
> With my patch,  the lb_value or lb_factor needs not  to have a special
> value  to handle  local workers.  Thus  lb_value is  modified at  each
> request handled by the worker.
> Feedback is welcome, testing of jk2 needs to be done.
> Mathias.


Dipl.-Inform. Bernd Koecke
Schlund+Partner AG
Fon: +49-721-91374-0

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