We continue to study the teachings of&nbsp;Designing Data-Intensive Applications, while Michael’s favorite book series might be the Twilight series, Joe blames his squeak toy chewing habit on his dogs, and Allen might be a Belieber. Head over to&nbsp;https://www.codingblocks.net/episode121&nbsp;to find this episode’s full show notes and join in the conversation, in case you’re reading these show notes via your podcast player. Sponsors  Educative.io&nbsp;– Level up your coding skills, quickly and efficiently. Visit&nbsp;educative.io/codingblocks&nbsp;to get 20% off any course or, for a limited time, get 50% off an annual subscription.  Survey Says          With the new year coming, what kind of learning resolution do you plan on setting? I plan to learn ... Take the survey at: https://www.codingblocks.net/episode121.          News  So many new reviews to be thankful for! Thanks for making it a point to share your review with us:  iTunes: bobby_richard, SeanNeedsNewGlasses, Teshiwyn, vasul007, The Jin John Stitcher: HotReloadJalapeño, Leonieke, Anonymous, Juke0815   Joe was a guest on&nbsp;The Waffling Taylors. Check out the entire three episode series:&nbsp;Squidge The Ring,&nbsp;Jay vs Doors,&nbsp;and&nbsp;Exploding Horses. Be aware of “free” VPNs.  This iOS Security App Shares User Data With China: 8 Million Americans Impacted&nbsp;(Forbes) Facebook shuts down Onavo VPN app following privacy scandal&nbsp;(Engadget)   Allen will be speaking at NDC { London } where he will be giving his talk&nbsp;Big Data Analytics in Near-Real-Time with Apache Kafka Streams. Be sure to stop by for your chance to kick him in the shins! (ndc-london.com)  Scalability  Increased load is a common reason for degradation of reliability. Scalability is the term used to describe a system’s ability to cope with increased load. It can be tempting to say X scales, or doesn’t, but referring to a system as “scalable” really means how good your options are. Couple questions to ask of your system:  If the system grows in a particular way (more data, more users, more usage), what are our options for coping? How easy is it to add computing resources?    Describing Load  Need to figure out how to describe load before before we can truly answer any questions. “Load Parameters” are the metrics that make sense to measure for your system. Load Parameters are a measure of stress, not of performance. Different parameters may matter more for your system. Examples for particular uses may include:  Web Server: requests per second Database: read/write ratio Application: # of simultaneous active users Cache: hit/miss ratio   This may not be a simple number either. Sometimes you may care more about the average number, sometimes only the extremes.  Describing Performance  Two ways to look at describing performance:  How does performance change when you increase a load parameter, without changing resources? How much do you need to increase resources to maintain performance when increasing a load parameter?   Performance numbers measure how well your system is responding. Examples can include:  Throughput (records processed per second) Response time    Latency vs Response Time  Latency is how long a request is waiting to be handled, awaiting service. Response time is the total time it takes for the client to see the response, including any latency.  What do you mean by “numbers”?  Performance numbers are generally a set of numbers: i.e. minimum, maximum, average, median, percentile. Sometimes the outliers are really important.  For example, a game may have an average of 59 FPS but that number might drop to 10 FPS when garbage collection is running. Average may not be your best measure if you want to see the typical response time.   For this reason it’s better to use percentiles.  Consider the median (sort all the response times and the one in the middle is the median). Median is known as the 50th percentile or P50.  That means that half of...

Designing Data-Intensive Applications – Scalability

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