To clarify, writes have no *immediate* cpu cost from adding the write to the memtable, however the compression overhead cost is paid when writing out a new SSTable (whether from flushing a memtable or compacting), correct?
So it sounds like when reads >> writes then Tushar's comments are accurate, but for a high write workload flushing and compactions would create most of the overhead. On Tue, Nov 3, 2015 at 6:03 PM, Jon Haddad <jonathan.had...@gmail.com> wrote: > You won't see any overhead on writes because you don't actually write to > sstables when performing a write. Just the commit log & memtable. > Memtables are flushes asynchronously. > > On Nov 4, 2015, at 1:57 AM, Tushar Agrawal <agrawal.tus...@gmail.com> > wrote: > > For writes it's negligible. For reads it makes a significant difference > for high tps and low latency workload. You would see up to 3x higher cpu > with LZ4 vs no compression. It would be different for different h/w > configurations. > > > Thanks, > Tushar > (Sent from iPhone) > > On Nov 3, 2015, at 5:51 PM, Dan Kinder <dkin...@turnitin.com> wrote: > > Most concerned about write since that's where most of the cost is, but > perf numbers for a any workload mix would be helpful. > > On Tue, Nov 3, 2015 at 3:48 PM, Graham Sanderson <gra...@vast.com> wrote: > >> On read or write? >> >> https://issues.apache.org/jira/browse/CASSANDRA-7039 and friends in 2.2 >> should make some difference, I didn’t immediately find perf numbers though. >> >> On Nov 3, 2015, at 5:42 PM, Dan Kinder <dkin...@turnitin.com> wrote: >> >> Hey all, >> >> Just wondering if anyone has done seen or done any benchmarking for the >> actual CPU overhead added by various compression algorithms in Cassandra >> (at least LZ4) vs no compression. Clearly this is going to be workload >> dependent but even a rough gauge would be helpful (ex. "Turning on LZ4 >> compression increases my CPU load by ~2x") >> >> -dan >> >> >> > > > -- > Dan Kinder > Senior Software Engineer > Turnitin – www.turnitin.com > dkin...@turnitin.com > > > -- Dan Kinder Senior Software Engineer Turnitin – www.turnitin.com dkin...@turnitin.com
