On Sun, 19 Jul 2015, David Casier AEVOO wrote: > Hi, > I have a question about PGLog and RAM consumption. > > In the documentation, we read "OSDs do not require as much RAM for regular > operations (e.g., 500MB of RAM per daemon instance); however, during recovery > they need significantly more RAM (e.g., ~1GB per 1TB of storage per daemon)" > > But in fact, all pg log are read in the start of ceph-osd daemon and put in > RAM ( pg->read_state(store, bl); ) > > Is this normal behavior or I have a defect in my environment? There are two tunables that control how many pg log entries we keep around. When teh PG is healthy, we keep ~1000, and when the PG is degraded, we keep more, to expand the time window over which a recovering OSD will be able to do regular log-based recovery instead of a more expensive backfill. This is one source of additional memory. Others are the missing sets (lists of missing/degraded objects) and messages/data/state associated with objcts that are being recovered/copied. Note that the numbers in teh documentation are pretty rough rules of thumb. At some point it would be great to build a model for how much RAM the osd consumes as a function of the various configurables (pg log size, pg count, avg object size, etc.). sage -- 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
