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From Gabriel Lavoie <glav...@gmail.com>
Subject Re: Question about JCLOUDS-658 Jira issue
Date Wed, 12 Nov 2014 16:23:14 GMT
Hi Adrian/Andrew,
    thank you very much for your replies. This information will be really
helpful to continue my evaluation of jclouds.

Cheers,


Gabriel

2014-11-12 0:34 GMT-08:00 Andrew Gaul <gaul@apache.org>:

> 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/
>



-- 
Gabriel Lavoie
glavoie@gmail.com

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