|How to gather various statistics with respect to CDB and PDB in 12c? [message #641841]
|Tue, 25 August 2015 10:19
Registered: August 2015
1. Do we need to collect all of these stats in CDB
fixed objects statistics
2. In 11g, dictionary statistics had to be collected separately, Is there a change in 12c and did they combine optimizer stats and dictionary stats? Is it documented anywhere?
3. Do we need to collect all of those 4 stats in every PDB and here are the points which should be clarified before deciding this.
a. There is only one instance and shared by all PDBs
b. There is only one server that is shared by all PDBs (not even bringing in RAC to keep the confusion minimum)
c. There is only one spfile/pfile and the optimizer characteristics are controlled at the instance CDB level rather than the PDB level.
with that said,
i. Aren't there only one set of x$ views in each instance regardless of how many PDBs you have? If that's the case it would make more sense to collect the stats at the CDB level and share the information in all PDBs
ii. Since the server is shared, CPU information (how many cores, how many sockets and speed etc.,) is not going to different for each PDB, so why would you need to collect this information in every PDB?
iii. Same concept applies to the I/O characteristics of the system as well. Even if we assume they are collecting the I/O load of each PDB, it would make more sense to consolidate all them at the CDB level, otherwise every PDB will have its own data and it wouldn't know about the other PDBs and their load.
iv. Also when you plug in a PDB from one CDB to another, you don't want to carry the system statistics from the old system to the new system, which could be completely different.