s3cache: A caching layer around s3mpi calls.
In robertzk/s3mpi: R message passing interface using S3 storage

Fetching large files from the S3 MPI can be expensive when performed multiple times. This method allows one to add a caching layer around S3 fetching. The user should specify the configuration option options(s3mpi.cache = "some/dir"). The recommended cache directory (where files will be stored) is "~/.s3cache".

1	s3cache(s3key, value)

`s3key`	character. The full S3 key to attempt to read or write to the cache.
`value`	ANY. The R object to save in the cache. If missing, a cache read will be performed instead.