Question: on my object, I have a link to `'product.product'` as many2one field, in my object view, I registered `product_id` field:

```
class my_object(osv.osv):

    _columns = {

         'product_id': fields.many2one('product.product', 'Product'),

    }

```

`<field context="{'group_by':'categ_id','search_default_filter_to_sell':1}" name="product_id" />`

**(Please take a look at 'product.product' search view at addons/products/product\_view.xml)**

when i select `"Search More ..."` option from dropdown, the tree view will just filtered by `'search_default_filter_to_sell'` and `group_by` filter is not activated, I tried all available `group_by` filters from `product.product` search view and no thing happen.

all objects with search-view that have group\_by filter has this issue when you link them with many2one relation.

is this a bug? or i did something wrong?

I'm using Openerp v7.0, windows7, firefox21.

Answer: 
If you have multiple threads enabled, CPLEX will use the concurrent optimizer. That means it runs the dual-simplex in one thread and the barrier algorithm in the remaining other threads. CPLEX reports the answer of the algorithm that finishes first. So if you have 6 cores, then it it likely using 1 thread for dual simplex and 5 threads for barrier. When you try to solve 3 LPs simultaneously, they are stealing cycles from each other. You can use just the dual simplex (which always uses just 1 thread) by setting the parameter RootAlg to 2. You could also set the parameter [AuxRootThreads](http://pic.dhe.ibm.com/infocenter/cosinfoc/v12r2/index.jsp?topic=/ilog.odms.cplex.help/Content/Optimization/Documentation/CPLEX/_pubskel/CPLEX1053.html) to limit the number of threads used by each LP solve.
 You should check which of the algorithms (Primal, Dual, or Barrier) work better on your problem. If Barrier, which can take advantage of multiple threads, works the best, you might be better off running each model serially and letting CPLEX do the parallelization.
First, let me highlight that the comment by [T.J.Crowder](https://stackoverflow.com/users/157247/t-j-crowder) is right. Generally speaking, the real speed-up could not be linear in a multi-thread approach. In fact, consider that: 1) there are other processes that runs on the machine, not only yours; 2) the CPU architecture is very important, as well as other hardware (mother board, RAM, etc.), then these may affect the performance of your algorithm.

I suggest to play with the several options included in CPLEX, e.g. with [`parallel mode switch`](http://pic.dhe.ibm.com/infocenter/cosinfoc/v12r2/index.jsp?topic=/ilog.odms.cplex.help/Content/Optimization/Documentation/CPLEX/_pubskel/CPLEX1022.html). 

Finally, another important consideration is about your question: you are presuming that your implementation is good, but there is no evidence about that.