Just a quick post regarding OEM 12c installation where recently I had to install OEM 12c and during the repository configuration step the installation fails with error:
ORA-12801: error signaled in parallel query server P151
This was caused by a known bug which requires decreasing the number of parallel queries of the repository databases and start over the installation. The database had cpu_count set to 64 and parallel_max_servers to 270. After setting the parallel_max_servers to lower value the installation completed successfully.
For more information refer to:
EM 12c: Enterprise Manager Cloud Control 12c Installation Fails At Repository Configuration With Error: ORA-12805: parallel query server died unexpectedly (Doc ID 1539444.1)