On Tue, Feb 28, 2012 at 10:07 AM, Noah Watkins <[email protected]> wrote: > I'm curious about what performance implications there may be when using > rados_ioctx_locator_set_key. > > If a large number of objects are forced into a single PG using a fixed > locator key, are there performance implications for subsequent look-ups by > object name? Is some type of index structure used under the hood since the PG > isn't chosen using locator_key = object_name?
The placement path with a locator defined is the same as without a locator defined — the difference is that with a locator you're placing based on hash(locator) instead of hash(object_name). Used sparingly (mapping a couple objects to the same locator), this won't have any performance implications. Used to great excess, you can run into a variety of problems: reducing the amount of hash space used, increasing variance in PG sizes forcing a large number of objects into a single folder on the OSD disk store (because it won't split apart a single hash) ...actually, that's all I can come up with off-hand. -Greg -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
