jm + p99   6

A Twitter thread about where P99s came from
"If you're wondering what "P-four-nines" means, it's the latency at the 99.99th percentile, meaning only one in 10,000 requests has a worse latency. Why do we measure latency in percentiles? A thread about how how it came to be at Amazon..."

This is a great thread from Andrew Certain, who managed the Performance Engineering team at Amazon in 2001. Percentiles, particularly for latency and performance measurement, were one of the big ideas which hit me like a ton of bricks when I joined Amazon, as they had been adopted whole-heartedly across the company by that stage.
p99  percentiles  quantiles  history  performance  analysis  measurement  metrics  amazon  aws  pmet 
28 days ago by jm
You CAN Average Percentiles
John Rauser on this oft-cited dictum of percentile usage in monitoring, and when it's wrong and it's actually possible to reason with averaged percentiles, and when it breaks down.
statistics  percentiles  quantiles  john-rauser  histograms  averaging  mean  p99 
july 2016 by jm
Testing fork time on AWS/Xen infrastructure
Redis uses forking to perform persistence flushes, which means that once every 30 minutes it performs like crap (and kills the 99th percentile latency). Given this, various Redis people have been benchmarking fork() times on various Xen platforms, since Xen has a crappy fork() implementation
fork  xen  redis  bugs  performance  latency  p99 
october 2014 by jm
Most page loads will experience the 99th percentile response latency
MOST of the page view attempts will experience the 99%'lie server response time in modern web applications. You didn't read that wrong.
latency  metrics  percentiles  p99  web  http  soa 
october 2014 by jm
AnandTech - The Intel SSD DC S3700: Intel's 3rd Generation Controller Analyzed
Interesting trend; Intel moved from a btree to an array-based data structure for their logical-block address indirection map, in order to reduce worst-case latencies (via Martin Thompson)
latency  intel  via:martin-thompson  optimization  speed  p99  data-structures  arrays  btrees  ssd  hardware 
november 2012 by jm

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