Gotchas Gotchas in in Memcached Memcached and Friends and Friends Neil Neil Gunther Gunther, , Performance Dynamics Performance Dynamics Shanti Subramanyam Shanti Subramanyam, , Oracle Corp Oracle Corporation oration Stefan Stefan Parvu Parvu, , Oracle Finland Oracle Finland
• Qualitative scalability – Scale up, e.g., big SMP servers – Scale out,e.g, many cheap servers (Unis) • Quantitative scalability – What this talk is about – Need controlled measurements – Need numbers to see cost-benefit
• You know you need it – The planning bit, especially – Data ain’t information – Info is hidden in the data • Just like finance, you need a model Metrics + Models == Information
Controlled Measurements? Trying to predict scalability by looking at time series data is like trying to predict the stock mkt by watching the DJX ticker
Measurements Measurements Need x-axis to be load (N) defined in terms of processes or users Need throughput measured in steady state (which this isn’t)
Among Friends Scalability as a function of Scalability as a function of virtual virtual users users ( (“ “friends friends” ”) not threads ) not threads
be broken Old scaling rules will be broken • Current scale-out strategy relies on using older cheap hardware • Older hardware is often single CPU – Single-threadedness of mcd is ok • Newer hardware will be multicore – New hardware is faster with lots of cores – But mcd won’t be able to utilize all cores – Multiple mcd instances are mgmt headache
mcd versions are thread limited – OK for older uniprocessor servers – Not OK for deployment on new multicores – Reason: unused processor capacity • Controlled measurements – Not time-series prod data – Steady state throughput • Quantify scalability – Data + Models == Information – Goal is reduce contention (α) and coherency (β) – Nmax: increased from 6 to 48 threads