The only downside of compression is it does cause more memory pressure. I can imagine something like repair could confound this. Since it would seem like building the merkle tree would involve decompressing every block on disk.
I have been attempting to determine if the block size being larger or smaller has any effect on memory pressure. On Sat, Mar 10, 2012 at 4:50 PM, Peter Schuller <peter.schul...@infidyne.com> wrote: >> However, when I run a repair my CMS usage graph no longer shows sudden drops >> but rather gradual slopes and only manages to clear around 300MB each GC. >> This seems to occur on 2 other nodes in my cluster around the same time, I >> assume this is because they're the replicas (we use 3 replicas). Parnew >> collections look about the same on my graphs with or without repair running >> so no trouble there so far as I can tell. > > I don't know why leveled/snappy would affect it, but disregarding > that, I would have been suggesting that you are seeing additional heap > usage because of long-running repairs retaining sstables and delaying > their unload/removal (index sampling/bloom filters filling your heap). > If it really only happens for leveled/snappy however, I don't know > what that might be caused by. > > -- > / Peter Schuller (@scode, http://worldmodscode.wordpress.com)
