Hi Xiaoxi, cc-ing ceph-devel for posterity ;) On 11/27/2015 08:25 AM, Chen, Xiaoxi wrote: > Hi joao, > > I am a bit confuse about the difference between in > Paxos::trim() and PaxosService::trim? Seems they did same work basically? In essence, both have the same purpose: remove no longer needed versions from the monitor store. They do, however, focus on different kinds of versions. The main difference is the way the Paxos class and PaxosService access the store. PaxosService provides an abstraction to services (e.g., OSDService) such that each service, in a way, doesn't have to care much how their keys are named. PaxosService handles this by suffixing each key with the service's name (e.g., osdmap). Also, services tend to keep both incremental and full versions, and the PaxosService class is also aware of this. Hence, PaxosService::trim() removes both incremental and full versions when the service prescribes a trim, while making sure that only versions related to that service are actually removed -- upon trim, the OSDMonitor will not remove MonmapMonitor's versions. On the other hand, Paxos::trim() deals solely with paxos versions. One should also take into account that each service may have different criteria on when to trim -- and PaxosService's abstraction takes that into account -- while the Paxos class' criteria is pretty straightforward: keep a minimum of N versions and a maximum of M. Then you have PaxosService::maybe_trim(), where most of the logic on deciding "when to trim" is located, even though ascertaining the bounds are delegated to the services themselves. Again, given PaxosService is an abstraction for the various services, you also get a bunch of logic related to the nuances of removing versions from a paxos service, such as allowing each service to trim additional stuff beyond the incremental and full versions. In the end, maybe we could find a generic function that could serve both the Paxos class and PaxosServices, but these are both simple enough that I don't think that is warranted. I have the feeling we would always end up with at least one additional function (the generic one) and would maintain most of the logic on both Paxos::trim() and PaxosService::trim() in place anyway, and I don't think that's worth it. Hope this helps clarifying things a bit. -Joao -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
