update default overcommit

This change updates the cpu and ram initial
allocation ratios to 4.0 and 1.0 to reflect
the typical values that are suitable for non web
hosting workloads.

Change-Id: I283eb270a4e47da15cf01d098b4f3952f7b5b570
implements: bp/nova-change-default-overcommit-values

1 files changed, 21 insertions, 0 deletions

diff --git a/releasenotes/notes/update-initial-allocation-defaults-94106033b66b8fa0.yaml b/releasenotes/notes/update-initial-allocation-defaults-94106033b66b8fa0.yaml
new file mode 100644
index 0000000000..937c8d1c8a
--- /dev/null
+++ b/releasenotes/notes/update-initial-allocation-defaults-94106033b66b8fa0.yaml
@@ -0,0 +1,21 @@
+---
+upgrade:
+  - |
+    In this release the default values for the initial ram and cpu allocation
+    ratios have been updated to 1.0 and 4.0 respectively. This will not
+    affect any existing compute node resource providers but the new default
+    will take effect on the creation of new resource providers.
+other:
+  - |
+    The default initial allocation ratios enabled ram over commit by default
+    with a factor of ``1.5``. This value was chosen early in nova's history
+    as the predominant workload was web hosting or other light weight
+    virtualization. Similarly the default initial cpu allocation ratio
+    defaulted to 16. As more demanding workload from telco, enterprise,
+    scientific and governmental users became the norm the initial values we
+    had chosen became less and less correct overtime. These have now been
+    updated to reflect a more reasonable default for the majority of our users.
+    As of this release the initial ram allocation value is 1.0 disabling
+    overcommit by default for new compute nodes and the initial cpu allocation
+    ratio is now 4.0 which is a more reasonable overcommit for non idle
+    workloads.