Links for 2013-02-18

  • Fatcache

    from Twitter — ‘a cache for your big data. Even though memory is thousand times faster than SSD, network connected SSD-backed memory makes sense, if we design the system in a way that network latencies dominate over the SSD latencies by a large factor. To understand why network connected SSD makes sense, it is important to understand the role distributed memory plays in large-scale web architecture. In recent years, terabyte-scale, distributed, in-memory caches have become a fundamental building block of any web architecture. In-memory indexes, hash tables, key-value stores and caches are increasingly incorporated for scaling throughput and reducing latency of persistent storage systems. However, power consumption, operational complexity and single node DRAM cost make horizontally scaling this architecture challenging. The current cost of DRAM per server increases dramatically beyond approximately 150 GB, and power cost scales similarly as DRAM density increases. Fatcache extends a volatile, in-memory cache by incorporating SSD-backed storage.’

    (tags: twitter ssd cache caching memcached memcache memory network storage)

  • Passively Monitoring Network Round-Trip Times – Boundary

    ‘how Boundary uses [TCP timestamps] to calculate round-trip times (RTTs) between any two hosts by passively monitoring TCP traffic flows, i.e., without actively launching ICMP echo requests (pings). The post is primarily an overview of this one aspect of TCP monitoring, it also outlines the mechanism we are using, and demonstrates its correctness.’

    (tags: tcp boundary monitoring network ip passive-monitoring rtt timestamping)

  • drug cartel-controlled mobile comms networks

    “The Mexican military has recently broken up several secret telecommunications networks that were built and controlled by drug cartels so they could coordinate drug shipments, monitor their rivals and orchestrate attacks on the security forces. A network that was dismantled just last week provided cartel members with cellphone and radio communications across four northeastern states. The network had coverage along almost 500 miles of the Texas border and extended nearly another 500 miles into Mexico’s interior. Soldiers seized 167 antennas, more than 150 repeaters and thousands of cellphones and radios that operated on the system. Some of the remote antennas and relay stations were powered with solar panels.”

    (tags: mexico drugs networks mobile-phones crime)

  • Heroku finds out that distributed queueing is hard

    Stage 3 of the Rap Genius/Heroku blog drama. Summary (as far as I can tell): Heroku gave up on a fully-synchronised load-balancing setup (“intelligent routing”), since it didn’t scale, in favour of randomised queue selection; they didn’t sufficiently inform their customers, and metrics and docs were not updated to make this change public; the pessimal case became pretty damn pessimal; a customer eventually noticed and complained publicly, creating a public shit-storm. Comments: 1. this is why you monitor real HTTP request latency (scroll down for crazy graphs!). 2. include 90/99 percentiles to catch the “tail” of poorly-performing requests. 3. Load balancers are hard. http://aphyr.com/posts/277-timelike-a-network-simulator has more info on the intricacies of distributed load balancing — worth a read.

    (tags: heroku rap-genius via:hn networking distcomp distributed load-balancing ip queueing percentiles monitoring)

  • Unhelpful Graphite Tips

    10 particularly good — actually helpful — tips on using the Graphite metric graphing system

    (tags: graphite ops metrics service-metrics graphing ui dataviz)

  • Literate Jenks Natural Breaks and How The Idea Of Code is Lost

    A crazy amount of code archaeology to discover exactly an algorithm — specifically ‘Jenks natural breaks”, works, after decades of cargo-cult copying (via Nelson): ‘I spent a day reading the original text and decoding as much as possible of the code’s intention, so that I could write a ‘literate’ implementation. My definition of literate is highly descriptive variable names, detailed and narrative comments, and straightforward code with no hijinks. So: yes, this isn’t the first implementation of Jenks in Javascript. And it took me several times longer to do things this way than to just get the code working. But the sad and foreboding state of this algorithm’s existing implementations said that to think critically about this code, its result, and possibilities for improvement, we need at least one version that’s clear about what it’s doing.’

    (tags: jenks-natural-breaks algorithms chloropleth javascript reverse-engineering history software copyright via:nelson)

  • don’t order a Raspberry Pi from RS

    I’ve been waiting 24 days for mine so far. Frankly amazing they are so apparently inept, particularly since it seems in breach of EU distance selling regulation if they go beyond 30 days without an update. They’ve just posted this:

    Quick update- we received our delivery of raspberry pi’s last week and as of Friday we had shipped up to order reference 1010239854. We will continue daily to get your orders shipped out as quickly as we possibly can; so that you will all receive your raspberry pi’s shortly. Many thanks everyone for your patience and again apologies for the delay in the dispatch update message on the Pi Store which I know has caused some confusion.

    (tags: rs raspberry-pi inept etailers uk e-commerce shopping hardware)

  • more details on the UK distance selling regulations governing Raspberry Pi RS orders

    ‘my understanding is that according to the Distance Selling Regulations […], unless you agreed otherwise with RS, then they were obligated to fulfill their side of the contract within thirty days from the day after you ordered, and if they were unable to do so they were also obligated to inform you that they could not and repay you within thirty days;ons (more info here in a nice, easy-to-read format), unless you agreed otherwise with RS, then they were obligated to fulfill their side of the contract within thirty days from the day after you ordered, and if they were unable to do so they were also obligated to inform you that they could not and repay you within thirty days’

    (tags: rs shopping etailers inept distance-selling uk law)

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