Parallel option performing worse on cluster I'm trying out oracles parallel option on a cluster and surprisingly I am getting worse results with the parallel option. I was expecting some improvement with the parallel option but certainly not worse results. I am wondering why this is the case, and if there is anything wrong with the way I am using the parallel option on my cluster. 

I am using a degree of 4 when the number of CPU's I have is 8. I have tried adding parallel to the cluster directly ALTER CLUSTER cluster PARALLEL 4 as well as at the statement on both the index /*+ PARALLEL_INDEX(clust_index, 4) */and tables /*+ PARALLEL(4) */, 

Here is my trace from the parallel:



Without parallel:
If you want to run in parallel you have to design for it. Things to consider is using partitions so they can be scanned in parallel. Don't forget that parallelism in general will try to use full scans on segments. Partition pruning can help reducing the size of your scans.

If you really are using pq for this sort of small queries, make sure you have enough PQ slaves ready for use. Otherwise, the starting of new slaves is added as overhead to your query. Not that bad for dss type queries that run for hours but deadly for short running queries.

Also think about using queuing your PQ queries to guarantee that when a query starts, it has all the slaves it needs. This can be done in Oracle Resource Manager.