The question of how to backup an index comes up every so often on the
lists. Backing up and index is also clearly an important fundamental
admin task that many applications need to do for fault tolerance.
In the past you were forced to stop & block all changes to your index,
perform the backup, and then resume changes. But many applications
cannot afford a potentially long pause in their indexing.
With the addition of DeletionPolicy (
LUCENE-710), it's now possible to
do a "live backup", which means backup your index in the background
without pausing ongoing changes to the index. This
SnapshotDeletionPolicy just has to mark the chosen commit point as not
deletable, until the backup finishes.