elasticsearch/elasticsearch — pull request #4602 by s1monw (2014-01-03 12:58:08+00:00)
Title: Add NodeVersionAllocationDecider that prevent allocations that require forward compatibility.

Today during restart scenarios it is possible that we recover from a node that
has already been upgraded to version N+1. The node that we relocate to is
on version N and might not be able to read the index format from the node
we relocate from. This causes `IndexFormatToNewException` during
recovery but only after recovery has finished which can cause large
load spikes during the upgrade period.

Closes #4588