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Pelikan is Twitter's unified cache backend

Pelikan is Twitter's unified cache server.

Content

• Overview
  • Products
  • Features
• Build
• Usage
• Community
  • Stay in touch
  • Contributing
• Documentation
• License

Overview

After years of using and working on various cache services, we built a common framework that reveals the inherent architectural similarity among them.

By creating well-defined modules, most of the low-level functionalities are reused as we create different binaries. The implementation learns from our operational experiences to improve performance and reliability, and leads to software designed for large-scale deployment.

The framework approach allows us to develop new features and protocols quickly.

Products

Currently Pelikan yields three main products, all of which are backends/servers.

• pelikan_twemcache: a Twemcache replacement
• pelikan_slimcache: a Memcached-like server with ultra-low memory overhead- compared to Memcached/Redis, the per-key overhead is reduced by up to 90%
• pelikan_pingserver: an over-engineered, production-ready ping server useful as a tutorial and for measuring baseline RPC performance

Features

• runtime separation of control and data plane
• predictably low latencies via lockless data structures, worker never blocks
• per-module config options and metrics that can be composed easily
• multiple storage and protocol implementations, easy to further extend
• low-overhead command logger for hotkey and other important data analysis

Building Pelikan

Requirement

• platform: Mac OS X or Linux
• build tools: cmake (>=2.8)
• compiler: gcc (>=4.8) or clang (>=3.1)
• (optional) unit testing framework: check (>=0.10.0). See below.

Build

git clone https://github.com/twitter/pelikan.git
mkdir _build && cd _build
cmake ..
make -j

The executables can be found under ./_bin/

To run all the tests, including those on ccommon, run:

make check
# 'make test' works too

To skip building tests, replace the cmake step with the following:

cmake -DCHECK_WORKING=off ..

Install check

To compile and run tests, you will have to install check. Please follow instructions in the project.

Note: we highly recommend installing the latest version of check from source, as there are, unfortunately, a linker bug in packages installed by the current versions of brew (OS X), CentOS and Ubuntu LTS. The bug does not affect building executables.

Usage

Using pelikan_twemcache as an example, other executables are highly similar.

To get info of the service, including usage format and options, run:

_bin/pelikan_twemcache -h

To launch the service with default settings, simply run:

_bin/pelikan_twemcache

To launch the service with the sample config file, run:

_bin/pelikan_twemcache config/twemcache.conf

You should be able to try out the server using an existing memcached client, or simply with telnet.

$ telnet localhost 12321
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
set foo 0 0 3
bar
STORED

Attention: use admin port for all non-data commands.

$ telnet localhost 9999
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
version
VERSION 0.1.0
stats
STAT pid 54937
STAT time 1459634909
STAT uptime 22
STAT version 100
STAT ru_stime 0.019172
...

Configuration

Pelikan is file-first when it comes to configurations, and currently is config-file only. You can create a new config file following the examples included under the config directory.

Tip: to get a list of config options for each executable, use -c option:

_bin/pelikan_twemcache -c

Community

Stay in touch

• Join our mailinglist or for questions and discussions
• Follow us on Twitter: @pelikan_cache
• Visit http://pelikan.io

Contributing

Please take a look at our community manifesto and coding style guide.

To get a sense of where things are going next, please visit our Roadmap wiki.

If you want to submit a patch, please follow these steps:

1. create a new issue
2. fork on github & clone your fork
3. create a feature branch on your fork
4. push your feature branch
5. create a pull request linked to the issue

Documentation

We have made progress and are actively working on documentation, and will put it on our website. Meanwhile, check out the current material under docs/

We also maintain a list of topics for upcoming blog posts. Please let us know what (else) interests you.

License

This software is licensed under the Apache 2.0 license, see LICENSE for details.