I'm having trouble getting Solr to use more than one thread during index optimizations.  I have the following in my solrconfig.xml:
 <mergeScheduler class="org.apache.lucene.index.ConcurrentMergeScheduler">
                <int name="maxThreadCount">6</int>
</mergeScheduler>
I had the same problem some time ago, but upgrading to Solr 1.4 solved the problem. Now it's happening again, with Solr 1.4. No matter what I set in the maxThreadCount, I only see one thread performing the merge when I profile the application.

Any idea what could be wrong?

Here are the details on my Solr deployment:
Solr Specification Version: 1.4.0.2009.10.14.08.05.59
Solr Implementation Version: nightly exported - yonik - 2009-10-14 08:05:59
Lucene Specification Version: 2.9.1-dev
Lucene Implementation Version: 2.9.1-dev 824988 - 2009-10-13 21:47:13
Thanks,
Gio.

: I'm having trouble getting Solr to use more than one thread during index
: optimizations.  I have the following in my solrconfig.xml:
:  <mergeScheduler class="org.apache.lucene.index.ConcurrentMergeScheduler">
:                 <int name="maxThreadCount">6</int>
: </mergeScheduler>

How many segments do you have?

I'm not an expert on segment merging, but i'm pretty sure the number of
threads it will use is limited based on the number of segments -- so even
though you say "use up to 8" it only uses one if that's all htat it can
use.

-Hoss