To improve optimizer estimates in case of skewed data distribution , histograms can be created. Prior to 12c, based on No. of distinct values (NDV) in a column two types of histograms could be created :
if no. of buckets >= NDV, frequency histogram is created and the optimizer makes accurate estimates.
If no. of buckets < NDV, height balanced histogram is created and accuracy of optimizer estimates depends on whether a key value is an endpoint or not.
The problem of optimizer mis-estimates in case of height balanced histograms is resolved to a large extent in Oracle Database 12c by introducing top-frequency and hybrid histograms which are created if no. of buckets < NDV.
I will present a webinar on “Histograms: Pre-12c and now” on Saturday, November 7th at 10:00 AM – 11:00 AM (IST) organized by All India Oracle User Group – North India Chapter.
This webinar explores Pre as well post-12c histograms while highlighting the top-frequency and hybrid histograms introduced in Oracle Database 12c.
Everyone can join this Live Webinar @
Hope to meet you at the webinar!!!
AIOUG meet “SANGAM – Meeting of Minds” is the Largest Independent Oracle Event in India, organized annually in the month of November. This year’s Sangam (Sangam15 - 7th Annual Oracle Users Group Conference) will be held in Hyderabad International Convention Centre, Hyderabad on Saturday 21st & Sunday 22nd November 2015.
I will be speaking at this year’s SANGAM about Oracle Database 12c new feature : Highly Available NFS (HANFS) over ACFS.
HANFS over ACFS enables highly available NFS servers to be configured using Oracle ACFS clusters. The NFS exports are exposed through Highly Available VIPs (HAVIPs), and this allows Oracle’s Clusterware agents to ensure that HAVIPs and NFS exports are always available. If the node hosting the export(s) fails, the corresponding HAVIP and hence its corresponding NFS export(s) will automatically fail over to one of the surviving nodes so that the NFS client continues to receive uninterrupted service of NFS exported paths.
My session will be held on Saturday November 21, 2015 from 5:10pm to 6:00pm in
Hall 5 (Ground Floor).
Hope to meet you there!!