Yeah that’s basically the case. RADOS support for xattrs significantly precedes the introduction of the omap concept and is perfectly acceptable to use but also kind of vestigial at this point. :) On Tue, Sep 11, 2018 at 12:43 PM Benjamin Cherian < benjamin.cher...@gmail.com> wrote:
> On Tue, Sep 11, 2018 at 10:44 AM Gregory Farnum <gfar...@redhat.com> > wrote: > >> <snip> >> In general, if the key-value storage is of unpredictable or non-trivial >> size, you should use omap. >> >> At the bottom layer where the data is actually stored, they're likely to >> be in the same places (if using BlueStore, they are the same — in >> FileStore, a rados xattr *might* be in the local FS xattrs, or it might >> not). It is somewhat more likely that something stored in an xattr will get >> pulled into memory at the same time as the object's internal metadata, but >> that only happens if it's quite small (think the xfs or ext4 xattr rules). >> > > Based on this description, if I'm planning on using Bluestore, there is no > particular reason to ever prefer using xattrs over omap (outside of ease of > use in the API), correct? > > Thanks, > Ben > > On Tue, Sep 11, 2018 at 10:44 AM Gregory Farnum <gfar...@redhat.com> > wrote: > >> On Tue, Sep 11, 2018 at 7:48 AM Benjamin Cherian < >> benjamin.cher...@gmail.com> wrote: >> >>> Hi, >>> >>> I'm interested in writing a relatively simple application that would use >>> librados for storage. Are there recommendations for when to use the omap as >>> opposed to an xattr? In theory, you could use either a set of xattrs or an >>> omap as a kv store associated with a specific object. Are there >>> recommendations for what kind of data xattrs and omaps are intended to >>> store? >>> >> >> In general, if the key-value storage is of unpredictable or non-trivial >> size, you should use omap. >> >> At the bottom layer where the data is actually stored, they're likely to >> be in the same places (if using BlueStore, they are the same — in >> FileStore, a rados xattr *might* be in the local FS xattrs, or it might >> not). It is somewhat more likely that something stored in an xattr will get >> pulled into memory at the same time as the object's internal metadata, but >> that only happens if it's quite small (think the xfs or ext4 xattr rules). >> >> If you have 250KB of key-value data, omap is definitely the place for it. >> -Greg >> >> >>> Just for background, I have some metadata i'd like to associate with >>> each object (total size of all kv pairs in object metadata is ~250k, some >>> values a few bytes, while others are 10-20k.) The object will store actual >>> data (a relatively large FP array) as a binary blob (~3-5 MB). >>> >>> >>> Thanks, >>> Ben >>> -- >>> Regards, >>> >>> Benjamin Cherian >>> _______________________________________________ >>> ceph-users mailing list >>> ceph-users@lists.ceph.com >>> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com >>> >>
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