Re: efficient removal of old objects

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(resending to list, sorry tv)

On Tue, Jan 31, 2012 at 5:02 PM, Tommi Virtanen
<tommi.virtanen@xxxxxxxxxxxxx> wrote:
>
> On Tue, Jan 31, 2012 at 16:33, Sage Weil <sage@xxxxxxxxxxxx> wrote:
> > Currently rgw logs objects it wants to delete after some period of time,
> > and an radosgw-admin command comes back later to process the log.  It
> > works, but is currently slow (one sync op at a time).
> >
> > A better approach would be to mark objects for later removal, and have the
> > OSD do it in some more efficient way.  wip-objs-expire has a client side
> > (librados) interface for this.
>
> Is there some reason why this would be significantly more performant
> when done by the OSD itself? It seems like the deletion times can be
> bucketed by time nicely, then each bucket just contains a set of ids
> -- a good fit for the map data type -- and the client for running this
> deletion just streams the bucket contents over and issues delete
> messages for everything. What makes that inherently slow?

Random access to random cold objects is generally slower than doing
the operations on a single pg. E.g., if doing it as part of the scrub,
then objects are accessed anyway and are hopefully cached.

>
> > Should this be generalized to saying "do these osd ops at time X" instead
> > of "delete at time X".  Then it could setxattr, remove, call into a class,
> > whatever.
>
> That sounds like a really complex API, for quite marginal gain.

I do agree that for the sake of a garbage collection it's an overkill, however,

>
> To make my point even clearer: point me to another data store that has
> that idiom.

I can see its use, and even if not, I'm sure that there would be users
who would need it. I don't think there's any relevance to the question
whether there's any data store that implements that.

Yehuda
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