> If every node in the cluster is running major compaction, would it be able to > answer any read request? And is it wise to write anything to a cluster > while it's doing major compaction?
Compaction is something that is supposed to be continuously running in the background. As noted, it will have a performance impact in that it (1) generates I/O, (2) leads to cache eviction, and (if you're CPU bound rather than disk bound) (3) adds CPU load. But there is no intention that clients should have to care about compaction; it's to be viewed as a background operation continuously happening. A good rule of thumb is that an individual node should be able to handle your traffic when doing compaction; you don't want to be in the position where you're just barely dealing with the traffic, and a node doing compaction not being able to handle it. -- / Peter Schuller (@scode, http://worldmodscode.wordpress.com)
