From 4a4697decb1e82f8749b594d28bcbc13cee503dd Mon Sep 17 00:00:00 2001
From: Klaus Aehlig <aehlig@google.com>
Date: Mon, 6 May 2013 15:22:54 +0200
Subject: [PATCH] Change design of algorithm for computing rolling reboots
Instead of computing a coloring for one condition first and then refining
it for the other condition, we can construct a graph with edges for all
conditions that prevent simultaneous reboots. This will not only result
in simpler code, but might also lead to better colorings.
Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>
---
doc/design-hroller.rst | 22 +++++++++++-----------
1 file changed, 11 insertions(+), 11 deletions(-)
diff --git a/doc/design-hroller.rst b/doc/design-hroller.rst
index 888f9a9dc..fade880e2 100644
--- a/doc/design-hroller.rst
+++ b/doc/design-hroller.rst
@@ -80,18 +80,18 @@ them (citation needed). As such we'll implement for now just the
In order to do that we can use the following algorithm:
1) Compute node sets that don't contain both the primary and the
- secondary for any instance. This can be done already by the current
- hroller graph coloring algorithm: nodes are in the same set (color)
- if and only if no edge (instance) exists between them (see the
- :manpage:`hroller(1)` manpage for more details).
-2) Inside each node set calculate subsets that don't have any secondary
- node in common (this can be done by creating a graph of nodes that
- are connected if and only if an instance on both has the same
- secondary node, and coloring that graph)
-3) It is then possible to migrate in parallel all nodes in a subset
- created at step 2, and then reboot/perform maintenance on them, and
+ secondary of any instance, and also don't contain the primary
+ nodes of two instances that have the same node as secondary. These
+ can be obtained by computing a coloring of the graph with nodes
+ as vertexes and an edge between two nodes, if either condition
+ prevents simultaneous maintenance. (This is the current algorithm of
+ :manpage:`hroller(1)` with the extension that the graph to be colored
+ has additional edges between the primary nodes of two instances sharing
+ their secondary node.)
+2) It is then possible to migrate in parallel all nodes in a set
+ created at step 1, and then reboot/perform maintenance on them, and
migrate back their original primaries, which allows the computation
- above to be reused for each following subset without N+1 failures
+ above to be reused for each following set without N+1 failures
being triggered, if none were present before. See below about the
actual execution of the maintenance.
--
GitLab