Back to that march 1 post.
> 1. lb_value += lb_factor
Ok, I see this I think. But this happens after step 2.
> 2. the highest lb_value gets server;
Am I reading this code wrong, or is it the LOWEST value that is getting
the server
/** Get one worker that is ready
*/
for( level=0; level<JK_LB_LEVELS; level++ ) {
for(i = 0 ; i < lb->workerCnt[level] ; i++) {
jk_worker_t *w=lb->workerTables[level][i];
if( w->mbean->disabled ) continue;
if( w->in_error_state ) continue;
if( w->lb_disabled ) continue;
if( rc==NULL ) {
rc=w;
currentLevel=level;
lb_min=w->lb_value;
continue;
}
if( w->lb_value < lb_min ) {
lb_min = w->lb_value;
rc = w;
currentLevel=level;
}
}
> 3. if lb_value > 255 lb_value = 0;
This hunk of code reads to me like: if the lb_value of the winning
server >255 then reset the lb_value of ALL workers on the level to their
lb_factor. (not 0)
if( rc->lb_value != 0 ) {
int newValue=rc->lb_value + rc->lb_factor;
if( newValue > 255 ) {
rc->lb_value=rc->lb_factor;
/* Roll over. This has 2 goals:
- avoid the lb factor becoming too big, and give a
chance to run to
workers that were in error state ( I think it's
cleaner than looking for "max" )
- the actual lb_value will be 1 byte. Even on the
craziest platform, that
will be an atomic write. We do a lot of operations on
lb_value in a MT environment,
and the chance of reading something inconsistent is
considerable. Since APR
will not support atomic - and adding a CS would cost
too much, this is actually
a good solution.
Note that lb_value is not used for anything critical
- just to balance the load,
the worst that may happen is having a worker stay
idle for 255 requests.
*/
for(i = 0 ; i < lb->workerCnt[currentLevel] ; i++) {
jk_worker_t *w=lb->workerTables[currentLevel][i];
w->lb_value=w->lb_factor;
}
} else {
rc->lb_value=newValue;
}
>
> default lb_factor is 1, the value of 2 is two times higher,
> so using 100 i not appropriate. Use the numbers up to 10.
> It will give you 90%-10% workload in favor with the one with
> value of 10.
> The maximum meaningful factor is 25.
>
> 1. lb_value += lb_factor
>
> 2. the highest lb_value gets server;
>
> 3. if lb_value > 255 lb_value = 0;
>
> That's the algorithm.
>
> Is it perfect?
> Probably it could be better.
The level parameter REALLY helps if you want a primary/secondary set of
servers.
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