On Mon, Nov 10, 2014 at 05:45:10PM -0800, Gabriel Lavoie wrote: > I'm currently reviewing the jclouds filesystem blobstore API. I > noticed that user metadata doesn't get saved with the 1.8.1 version, > but that a comment exists in the code regarding Java 7 and NIO > filestore attributes. I also found out with the JCLOUDS-658 that > jclouds 2.0 (unreleased) fixes the issue by using the NIO filestore > attributes. > > Regarding this issue and resolution: > - Is the filesystem API considered "production" safe or only suggested for > testing/debugging? > - I'm not sure about the solution of using the filesystem metadata store > to store metadata. Many (most?) filesystem archival/backup/explorer are > not aware of this metadata and it may get lost without the user knowing > about it. I would consider using this for testing, but never in a > production environment. > - Could an alternate way of storing metadata be implemented, for > example in a properties file named <id>.metadata stored alongside > with the object file? > - I could implement a file metadata storage by wrapping > FilesystemStorageStrategyImpl, but I don't think this is a good idea to > wrap it as I have to re-implement a few classes to have the dependency > injection work correctly.
The filesystem blobstore has traditionally been used for testing purposes and has a few caveats for production use. However, it should perform well enough for applications with a small number of objects (tens of thousands) and small object sizes (gigabytes). My primary concern for production use is that a filesystem is not a blobstore; a single node lacks the performance and reliability that a multi-node Swift installation provides. While Swift uses a filesystem to stores its blob data, it uses XFS with several tuning parameters and hashes object names into directory shards to avoid scalability limits. The filesystem blobstore has a few known issues; we will gladly accept patches for these: * scalability: returning a paginated list of objects creates the entire list in-memory * compatibility: lacks multi-part upload, some listing options not supported * error paths: writing partial objects or concurrently overwriting objects has different semantics than real object stores, especially on Windows * performance: excessive system calls on various code paths * metadata: 1.8.1 does not support user metadata and other attributes. The approach for future releases only works on Linux and Windows. Current JDK on Mac OS X does not support xattr (JDK-8030048). Using file extended attributes is the "right" way to store object metadata and allows other tools to interact with these objects instead of using a special format that only jclouds understands. However, I appreciate the practical reasons to prefer another approach; could you explore this issue further? Every solution has a trade-offs, for example storing in <id>.metadata file requires extra work when listing objects. You may want to consider using a second directory for metadata instead. Finally you might want to look at Jimfs which creates an in-memory filesystem provider; perhaps you could create an on-disk provider which stores extended attributes in some other way? -- Andrew Gaul http://gaul.org/