I really don't see how pushing the naming complexity into the local filesystem, where it adds lots of otherwise-useless inodes and dentries, is going to help us.
I like what Yehuda has here for its relative simplicity -- though I think we should just up the hash size enough that we don't need to handle collisions, and leave out the retry looping so as to make it simpler still -- but given the relative simplicity I think it might be nice to push all the name mangling into a flat space so that we can preserve the prefix- and post-fixing -- this would keep snapshots of one object more identifiable than hashing over the entire name like it's doing right now.
-Greg
On Thursday, April 21, 2011 at 12:32 PM, Tommi Virtanen wrote:
> On Thu, Apr 21, 2011 at 12:27:01PM -0700, Colin McCabe wrote:
> > I like this idea a lot. It does involve extra expense, but only for
> > long file names. It also avoids object name collisions completely.
> >
> > One additional idea: can we make the chunking configurable?
> > If we did a translation like this:
> > abcdefg -> abc/def/g
> > 123456789 -> 123/456/789
> >
> > prefix search would become a *lot* more efficient for rgw.
> > On the other hand, the filesystem layer doesn't care about prefix
> > search, so it could just configure the chunking to be after 200
> > characters or something (at which point it's basically a no-op.)
>
> The one big downside is that with configurable chunking, you no longer
> have an always correct 1:1 mapping between object and file.
>
> You might argue for always (not configurably) chunking at some
> smaller, fixed boundary, so on the average you'd need to readdir()
> less to serve a prefix search. I think this is what your last sentence
> refers to. But that means more overhead with the directories.
>
> The only real answers are available via benchmarks.
>
> --
> :(){ :|:&};:
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