Represents an operation or stat of a document in the search engine. This
Object is used as a communication and persisntance mechanism between the
changes made to entities and the thread processing the indec updates
author: ieb
The action REBUILD causes the indexer thread to rebuild the index from
scratch, refetching all entities This sould only ever appear on the
master record
The action REFRESH causes the indexer thread to refresh the search index
from the current set of entities. If a Rebuild is in progress, the
refresh will not overrise the rebuild