It's sequential per-sstable. If you are compacting a lot of sstables how closely this approximates "completely sequential" will deteriorate.
On Sun, Jul 24, 2011 at 1:18 PM, Francois Richard <frich...@xobni.com> wrote: > Jonathan, > > Are you sure that the reads done for compaction are sequential with Cassandra > 0.6.13? This is not what I am observing right now. During a minor > compaction I usually observe ~ 1500 to 1900 r/s while rMB/s is barely around > 30 to 35MB/s. > > Just asking out of curiosity. > > > FR > > -----Original Message----- > From: Jonathan Ellis [mailto:jbel...@gmail.com] > Sent: Saturday, July 23, 2011 5:05 PM > To: user@cassandra.apache.org > Subject: Re: do I need to add more nodes? minor compaction eat all IO > > On Sat, Jul 23, 2011 at 4:16 PM, Francois Richard <frich...@xobni.com> wrote: >> My understanding is that during compaction cassandra does a lot of non >> sequential readsa then dumps the results with a big sequential write. > > Compaction reads and writes are both sequential, and 0.8 allows setting a > MB/s to cap compaction at. > > As to the original question "do I need to add more machines" I'd say that > depends more on whether your application's SLA is met, than what % io util > spikes to. > > -- > Jonathan Ellis > Project Chair, Apache Cassandra > co-founder of DataStax, the source for professional Cassandra support > http://www.datastax.com > -- Jonathan Ellis Project Chair, Apache Cassandra co-founder of DataStax, the source for professional Cassandra support http://www.datastax.com
