Author: stevel
Date: Thu Apr 9 12:37:46 2015
New Revision: 1672317
URL: http://svn.apache.org/r1672317
Log:
SLIDER-600 role history enhancements
Modified:
incubator/slider/site/trunk/content/design/rolehistory.md
Modified: incubator/slider/site/trunk/content/design/rolehistory.md
URL:
http://svn.apache.org/viewvc/incubator/slider/site/trunk/content/design/rolehistory.md?rev=1672317&r1=1672316&r2=1672317&view=diff
==============================================================================
--- incubator/slider/site/trunk/content/design/rolehistory.md (original)
+++ incubator/slider/site/trunk/content/design/rolehistory.md Thu Apr 9
12:37:46 2015
@@ -23,7 +23,6 @@
## Changes
-
### Slider 0.80-incubating
A major rework of placement has taken place, [Ãber-JIRA : placement phase
2](https://issues.apache.org/jira/browse/SLIDER-611)
@@ -38,6 +37,32 @@ that have reached their escalation timeo
request. YARN may still allocate relaxed instances on such nodes. That is:
there is no explicit
blacklisting, merely deliberate exclusion of unreliable nodes from explicitly
placed requests.
+Role History Reloading Enhancements
+
+How persisted role history has also been improved
[SLIDER-600]((https://issues.apache.org/jira/browse/SLIDER-600)
+
+1. Reloading of persistent history has been made resilient to changes in the
number of roles.
+1. If there are more roles in the history than the current set, the surplus
entries
+are discarded.
+1. If there are fewer, then the smaller set of roles are loaded
+1. The mapping of role name to role ID is persisted.
+1. There are tests to verify that the original role histories (those without
maps) are reloaded.
+
+There are no checks that the mapping of name to ID has not changed; the
current model
+is "don't do that". If it is done while an application instance is stopped,
the rebuilt
+placement may hurt performance of those roles which require an absolute
location.
+If it is done during AM restart, the AM will be unable to reliably rebuild its
+state model. SLIDER-849 proposes future handling of these situations. By
saving the current
+rolename to ID mappings, the placement history will be ready for such a
feature when it
+is implemented.
+
+The enhanced role history format is backwards compatible; there are tests to
verify that.
+However Slider 0.70 and earlier cannot process the 0.80 version entries. If
there are problems
+reloading entries there are two tactics
+
+1. Delete the JSON files
+2. Edit the most recent JSON file and delete any entry with the type
`RoleHistoryMapping`.
+
#### Placement policies
`strict` placement
