Got it. Thanks Greg for the response! Thanks, Guang
On Feb 26, 2014, at 11:51 AM, Gregory Farnum <[email protected]> wrote: > On Tue, Feb 25, 2014 at 7:13 PM, Guang <[email protected]> wrote: >> Hello, >> Most recently when looking at PG's folder splitting, I found that there was >> only one sub folder in the top 3 / 4 levels and start having 16 sub folders >> starting from level 6, what is the design consideration behind this? >> >> For example, if the PG root folder is '3.1905_head', in the first level, it >> only has one sub folder 'DIR_5' and then one sub folder 'DIR_0', and then >> 'DIR_9', under which there are two sub folders 'DIR_1' and 'DIR_9', starting >> from which, the next level has 16 sub folders. >> >> If we start splitting into 16 sub folders in the very first level, we may >> potential gain better performance with less dentry lookup (though most >> likely the root level been cached). > > It's an implementation detail of the FileStore (the part of the OSD > that stores data in the filesystem). Each of those folders represents > an ever-smaller division of the hash space that objects live in. The > more PGs you have, the less hash space each one covers, so there's > that trail of folders. > It's a bit unfortunate, because as you mention it involves more > metadata memory caching, but fixing it would require some fairly > detailed code in a critical path. The cost of fixing it and the risk > of breaking things haven't been worth it yet. > -Greg > Software Engineer #42 @ http://inktank.com | http://ceph.com
_______________________________________________ ceph-users mailing list [email protected] http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
