N single thread processes having better perf than 1 process N threads

[nshen]

Hi! I have an OCI application that makes one OCIEnvCreate call with OCI_THREADED attribute at main then creates N threads as needed; each thread with its own OCIServerAttach and OCISessionBegin.
We observed an interesting result when testing it using a wide stored procedure (with more than 450 I/O parameters). Both the response time and throughput of running 4 instances of this application as single thread app is better than running 1 instance of this app with 4 threads. We checked the server side there was no difference in the execution time. So it would seem to be a contention in the client side. Are there any parameter that I need to tune for multi-threaded OCI application at the Oracle client level?

We have tried both 8.1.7.4 and 9.2.0.3 clients on Widnwos and on Solaris.
Thank you!
Regards, Nancy

 

[jocave]

What sort of performance difference are we talking about-- 5% or 50%?

In general, since OCI would have to have some sort of locking or synchronization on the environment's data structures, I'd expect that N threads would behave slightly worse than N processes, but that it wouldn't be a significant difference (i.e. a few percent).

Is there anything in your code that could be causing additional locking?

Justin

 

[nshen]

It is below 10%: 7- 8%.
I was wondering that since each of my "thread" has its own OCIServerAttch/OCISessionBegin, will the OCI_THREADED attibute setting in the OCIEnvCreate actually hurt the multithreaded application.
Thanks In Advance!
Regards, Nancy

 

[jocave]

I believe that the OCI_THREADED attribute is required in this situation (but someone taking a detailed look at the OCI Programmer's Reference on

http://tahiti.oracle.com

might well prove this belief wrong).

I would generally think that a 7-8% performance loss would be about right for 4 threads contending for data structures in the OCI Environment object.

Justin