During one of the classes I taught about Exadata optimisations I had an interesting question:
If I am using VPD, will Exadata still offload the query?
Background is that we discussed function offloading, and the meta-view v$sqlfn_metadata. It turned out that SYS_CONTEXT() is not offloadable in 220.127.116.11.
For the next couple of weeks I'll be picking up various random notes I've made during the sessions that I've attended at OOW. This particular topic was also a problem discussed recently at one of my clients, so it's certainly worth to be published here.
In one of the optimizer related sessions it was mentioned that for highly volatile data - for example often found in Global Temporary Tables (GTT) - it's recommended to use Dynamic Sampling rather than attempting to gather statistics. In particular for GTTs gathering statistics is problematic because the statistics are used globally and shared across all sessions. But GTTs could have a completely different data volume and distribution per session so sharing the statistics doesn't make sense in such scenarios.
So using Dynamic Sampling sounds like a reasonable advice and it probably is in many such cases.