Cases Where Negative Performance Effects Are Most Likely To Occur
The greatest decrement in the performance of querying column‑partitioned tables occurs
when the following conditions take place.
Most or all of the columns in a column‑partitioned table are projected by a request.
The request is not selective.
The table being queried has thousands of column partitions.
The retrieval performance for a column‑partitioned table or join index is not good
when the number of column partition contexts that are available is significantly fewer
than the number of column partitions that must be accessed to respond to the query.
Note that there are at least eight available column partitions contexts. Depending
on your memory configuration, there may be more available contexts.
When this happens, consider the following remedies.
Reconfigure the table or join index to decrease the number of column partitions that
need to be accessed by combining column partitions so there are fewer of them.
If there is enough memory available, increase the setting for the DBS Control parameter
The table being queried has enough row‑partitioned levels that there are very few
physical rows in populated combined partitions, and the physical rows contain only
one or a few column partition values.