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<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Leveled</title>
<meta name="description" content="An overview of the Leveled Key/Value Store">
<meta name="author" content="Martin Sumner">
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<body>
<div class="reveal">
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<div class="slides">
<section>
<img width="450" height="600" data-src="images/ascot6201.jpg" alt="Bookmaker"/>
<p>http://martinsumner.github.io/presentations/leveled_euc#/</p>
</section>
<section>
<h2>My journey towards Erlang - 2004</h2>
<p align="left">I'm the network guy on a huge health database project</p>
<p align="left">Every problem looks like a network problem ...</p>
<p align="left">Started fixing things in the application ...</p>
<p align="right">... the business decided to fix things through process/management</p>
</section>
<section>
<h2>My journey towards Erlang - 2011</h2>
<p align="left">Spine now had:</p>
<ul>
<li>more than 3000 servers</li>
<li>more than 18 thousand people years behind it</li>
<li>more than £30m in change costs ... per change</li>
<li>total bill has passed £1bn </li>
</ul>
<p align="left">Is this the genuine cost of availability?</p>
<p align="left">Lets replace it with a fundamentally different approach</p>
</section>
<section>
<h2>My journey towards Erlang - 2014</h2>
<p align="left">Spine II Core goes live!</p>
<p align="left">Better than five nines availability since go-live</p>
<p align="left">Less than hundred people years to go-live</p>
<p align="left">Base of open-source Erlang products - Riak, RabbitMQ</p>
<p align="left">Architecture based on message passing between processes</p>
<p align="left">Architecture based on normalising failure</p>
<p align="left">Change is normal, weekly and automated</p>
</section>
<section data-background="#E6E68A">
<img width="450" height="600" data-src="images/challenge.jpg" alt="The Next Challenge"/>
</section>
<section data-background="#E6E68A">
<h2>Why An Erlang Key-Value Store?</h2>
<p align="left">Riak has been a rock - durability and availability</p>
<ul>
<li>I know it, and know of problems with it, and have a path to production</li>
</ul>
<p align="left">Pluggable backends, but no fully-featured Erlang backend</p>
<ul>
<li>Except for HanoiDB, so someone else thought this was worth doing</li>
</ul>
</section>
<section data-background="#E6E68A">
<img width="1200" height="450" data-src="images/LSM_paper.png" alt="LSM Paper Diagram"/>
</section>
<section data-background="#E6E68A">
<h2>Leveled - The Hypothesis</h2>
<p align="left">Disk I/O is an unpredictable bottleneck -> split VALUE</p>
<p align="right">... See also WiscKey, Badger</p>
<p align="left">Riak doesn't always need to know the value -> HEAD</p>
<p align="left">Store behaviour may differ by object -> TAG</p>
</section>
<section data-background="#E6E68A">
<img width="1000" height="650" data-src="images/leveldb_intro.png" alt="LevelDB Intro"/>
</section>
<section data-background="#E6E68A">
<img width="1000" height="650" data-src="images/leveled_overview.png" alt="Leveled Intro"/>
</section>
<!--
<section data-background="#E6E68A">
<h2>Leveled - The Actors</h2>
<p align="left"><b>Bookie</b> - marshalls requests at the front</p>
<p align="left"><b>Inker</b> - keeps permanent journal of keys and values</p>
<p align="left"><b>Penciller</b> - manages merge tree (ledger) of keys and metadata</p>
<p align="left"><b>Clerks</b> - support Inker and Penciller with background tasks</p>
</section>
-->
<!--
<section data-background="#E6E68A">
<h2>Leveled - The Inker and the Journal</h2>
<p align="left">The journal is a series of (DJ Bernstein) CDB files (as FSMs)</p>
<p align="left">The Inker has a manifest of sequence numbers -> FSMs -> Files</p>
<p align="left">The Inker has a Clerk to help with compaction</p>
<p align="left">Active journal file is mutable by append</p>
<p align="left">Other journal files are immutable until replacement</p>
</section>
-->
<!--
<section data-background="#E6E68A">
<img width="1000" height="650" data-src="images/leveled_inker_overview.png" alt="Inker"/>
</section>
-->
<!--
<section data-background="#E6E68A">
<h2>Leveled - The Penciller and the Ledger</h2>
<p align="left">The <b>Bookie</b> pushes lists of key/metadata in chunks</p>
<p align="left">The <b>Penciller</b> stacks recent chunks in memory, with hash-based index</p>
<p align="left">When in-memory count exceeds size of a sst file - persist and flush</p>
<p align="left">Each level consists of immutable SST files in key order</p>
<p align="left">Each level has a maximum number of files - excess triggers merge</p>
</section>
-->
<section data-background="#E6E68A">
<h2>Leveled - Operations</h2>
<p align="left"><b>PUT</b> - Inker commits to Journal, Bookie caches change to Ledger</p>
<p align="left"><b>GET</b> - Penciller fetches SQN, Inker fetches value</p>
<p align="left"><b>HEAD</b> - Penciller fetches metadata from Ledger</p>
<p align="left"><b>INDEX</b> - Additional key/metadata changes in Ledger</p>
<p align="left"><b>FOLD</b> - Efficient in key-ordered ledger through clones of Penciller</p>
<p align="left"><b>CLONE</b> - By manifest copy, with delete_pending file state, allowing reads in parallel</p>
</section>
<section data-background="#E6E68A">
<img width="1000" height="650" data-src="images/leveled_headvsget_overview.png" alt="Penciller"/>
</section>
<section data-background="#A3C2FF">
<img width="1000" height="650" data-src="images/wip.jpg" alt="Work In Progress"/>
</section>
<section data-background="#A3C2FF">
<h2>Leveled - Status</h2>
<p align="left">Functionally complete backend</p>
<p align="left">Initial integration testing into Riak</p>
<p align="left">Four months of cloud-based volume tests with improvements</p>
<p align="left">Good ct/eunit coverage, plus initial propery-based testing</p>
</section>
<section data-background="#A3C2FF">
<h2>Leveled - Volume tests</h2>
<p align="left">Significant throughput improvements where disk I/O is the dominant constraint</p>
<ul>
<li>With sync enabled (flushing each and every write)</li>
<li>With spinning disk drives not solid-state drives</li>
</ul>
<p align="left">Focused on testing without sync on SSD since</p>
<ul>
<li>Throughput advantage at > 4KB values</li>
<li>Advantage increases with value size</li>
<li>Lower mean PUT times, higher median GET times</li>
<li>Dramatic reduction in tail latency and volatility</li>
</ul>
</section>
<section data-background="#A3C2FF">
<img width="1600" height="500" data-src="images/ed_vs_db_compare.png" alt="Comparison with 2i"/>
</section>
<section data-background="#A3C2FF">
<h2>Leveled - The Hard Bits</h2>
<p align="left">Picking data structures in Erlang</p>
<p align="left">Handling OTP16 compatability</p>
<p align="left">Compacting the Journal (value store)</p>
<p align="left">Vnode coordination issues</p>
<p align="left">Avoiding long-tail blocking (e.g. the 40ms cast)</p>
<p align="left">Naming things</p>
</section>
<section data-background="#A3C2FF">
<h2>Leveled - Was it worth it?</h2>
<p align="left">Learned loads about Erlang - will continue to use</p>
<p align="left">Erlang/OTP coped well with my mistakes</p>
<p align="left">Pleasantly surprised by the throughput comparison</p>
<p align="left">Actors made more sense to me than objects</p>
<p align="left">Relevance increased by support issues with Riak</p>
<p align="left">Now progressing to pre-production testing on Spine</p>
</section>
<section data-background="#A3C2FF">
<img width="600" height="450" data-src="images/thank-you.jpg" alt="Comparison with 2i"/>
<p>@masleeds</p>
<p>https://github.com/martinsumner/leveled</p>
</section>
</div>
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