Previously, we could run into a situation where attempting to delete an
index due to a cluster state update would cause an unhandled exception
to bubble up to the ClusterService and cause the cluster state applier
to fail. The result of this situation is that the cluster state never
gets updated on the ClusterService because the exception happens before
all cluster state appliers have completed and the ClusterService only
updates the cluster state once all cluster state appliers have
successfully completed.
All other methods on IndicesService properly handle all exceptions and
not just IOExceptions, but there were two instances with respect to
index deletion where only IOExceptions where handled by the
IndicesService. If any other exception occurred during these delete
operations, the exception would be bubbled up to the ClusterService,
causing the aforementioned issues.
This commit ensures all methods in IndicesService properly capture all
types of Exceptions, so that the ClusterService manages to update the
cluster state, even in the presence of shard creation/deletion failures.
Note that the lack of updating the cluster state in the presence of such
exceptions can have many unintended consequences, one of them being
the tripping of the assertion in IndicesClusterStateService#removeUnallocatedIndices
where the assumption is that if there is an IndexService to remove with
an unassigned shard, then the index must exist in the cluster state, but if
the cluster state was never updated due to the aforementioned exceptions,
then the cluster state will not have the index in question.
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