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colmmacc's profile
Colm MacCárthaigh
Colm MacCárthaigh
Colm MacCárthaigh
@colmmacc

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Colm MacCárthaigh

@colmmacc

AWS, Apache, Crypto, Irish Music, Haiku, Photography

Seattle
notesfromthesound.com
Joined April 2008

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    1. Colm MacCárthaigh‏ @colmmacc 28 Aug 2018
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      Now if we repeat the same event, the impact is much smaller, just 25% of what it is was. Or more formally ...pic.twitter.com/8bcvECcNnu

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    2. Colm MacCárthaigh‏ @colmmacc 28 Aug 2018
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      The blast radius is now the number of customers divided by the number of shards. It's a big improvement. Do this! At AWS we call this cellularization and many of our systems are internally cellular. Our isolated regions, and availability Zones are a big famous macro example too.pic.twitter.com/PmolDBpl7W

      1 reply 6 retweets 21 likes
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    3. Colm MacCárthaigh‏ @colmmacc 28 Aug 2018
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      THIS is one reason why the personal health dashboard is so much better than the status page. The status for your cell might be very different than someone else's!

      2 replies 2 retweets 21 likes
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    4. Colm MacCárthaigh‏ @colmmacc 28 Aug 2018
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      ... anyway, back to Shuffle Sharding. With Shuffle Sharding we can do much better again than traditional sharding. It's deceptively simple. All we do is that for each customer we assign them to two servers pretty much at random.pic.twitter.com/0SISi2nsRL

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    5. Colm MacCárthaigh‏ @colmmacc 28 Aug 2018
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      So for example, the ❤️ customer is assigned to nodes 1 and 4. Suppose we get a problem request from ❤️ ? What happens?pic.twitter.com/5FZyFXIbJ4

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    6. Colm MacCárthaigh‏ @colmmacc 28 Aug 2018
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      Well ... it could take out nodes 1 and 4. So ❤️ is having a bad experience now. Amazing devops teams are on it, etc , but it's still not great for them. Not much we can do about that. But what about everyone else?pic.twitter.com/1J6oorA510

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    7. Colm MacCárthaigh‏ @colmmacc 28 Aug 2018
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      Well, if we look at ❤️'s neighbors. They're still fine! As long as their client is fault tolerant, which can be as simple as using retries, they can still get service. 😀 gets service from node 2 for example.pic.twitter.com/xJRpdK6Fgn

      1 reply 0 retweets 11 likes
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    8. Colm MacCárthaigh‏ @colmmacc 28 Aug 2018
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      O.k. let's PAUSE for a second and appreciate that. Same number of nodes. Same number of nodes for each customer. Same number of customers. Just by using MATH, we've reduced the blast radius to 1 customer! That's INSANE.

      2 replies 1 retweet 16 likes
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    9. Colm MacCárthaigh‏ @colmmacc 28 Aug 2018
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      The blast radius ends up getting really small. It's roughly proportionate to the factorial of the shard size (small) divided by the factorial of the number of nodes (which is big) ... so it can get really really small.pic.twitter.com/LmaffLA3tR

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    10. Colin Percival‏ @cperciva 4 Sep 2018
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      Replying to @colmmacc

      Surely this should be shardsize! / nodes^shardsize ? Trivial example, with 10 nodes and a shard size of 1, the blast radius is 1/10, not 1/10! .

      1 reply 0 retweets 0 likes
      Colm MacCárthaigh‏ @colmmacc 4 Sep 2018
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      Replying to @cperciva

      That's a better approximation, and the real math is later in the thread, but the main take-away for people to remember is that the bigger the count of nodes relative to the size of the shard .. the better, exponentially so.

      10:28 AM - 4 Sep 2018
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        2. Colin Percival‏ @cperciva 4 Sep 2018
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          Replying to @colmmacc

          Yes and no. Your formula makes it look like increasing the shard size increases the blast radius, but (up to reasonable limits) the exact opposite is true -- as long as shardsize = o(nodes) the blast radius *decreases* exponentially as the shard size increases.

          1 reply 0 retweets 0 likes
        3. Colm MacCárthaigh‏ @colmmacc 4 Sep 2018
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          Replying to @cperciva

          I still haven't even found a great to visualize or graph it that can help people get a feel for the sensitivities. It asymptotes so quickly, but I'd really love to nail a few paragraphs that could help people reason it out.pic.twitter.com/bZ1NXEd7AM

          1 reply 0 retweets 0 likes
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