Use filesystem backed index based on sha1 hash from canonical path.
data
+- abc
+- def
shared_paths
+- 8040f3f3 (/usr/shared/info-index)
+- abc -> ../../data/abc
+- def -> ../../data/def
+- 84e617a4 (/usr/shared/man-index)
+- abc -> ../../data/abc
+- def -> ../../data/def