[HADOOP-8046] Revert StaticMapping semantics to the existing ones, add DNS mapping diagnostics in progress

• Type: Bug
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 0.23.0, 0.24.0
• Fix Version/s: 0.23.2
• Assignee: Steve Loughran
• Reporter: Steve Loughran
• Created: 09/Feb/12 11:57
• Updated: 02/May/13 02:29
• Resolved: 18/Feb/12 12:58

Description

HADOOP-7878 still doesn't let the block manager switch to non-scripted topologies because the static mapping is still getting it wrong -it should just look at the configuration for a non-null script name, as per the usual ScriptBasedMapping, so as to keep tests backwards compatible.

In the process, make it possible to debug topologies by

1. #toString() operations to provide summary information, and for the CachedDNSToSwitchMapping, to include information on the inner mapping. ScriptBasedMapping to include the script name.
2. AbstractDNSToSwitchMapping} to offer a method {{getSwitchMap() to return a cloned map of the mapping, or null if this is not known.
3. AbstractDNSToSwitchMapping} to offer a method {{dumpTopology() to take this switch map and the toString() and generate a topology dump suitable for humans.
4. Implementing the switch map method for the standard mappings (Cached -> cached map, Static -> static map, Script -> null).
   These methods are all for debugging, but there is no reason not to use the contents of getSwitchMap() in service web pages providing details on the service's current view of the network topology, as it may differ from the expectations of the script author.

time: 30m to implement, 1h30 to write more tests and run them.

Issue Links

• is depended upon by: HDFS-2492 BlockManager cross-rack replication checks only work for ScriptBasedMapping
• is depended upon by: HADOOP-8049 Add entry point/script to do preflight checking of script resolution