Implementing High Availability Services for Memcached

Creating High Availability Services for Your Memcached Environment Presented by: Bill Takacs – Director, Product Management 25 August 2009

Memcached “A high performance, distributed memory object caching system, generic in nature, but intended for use in speeding up dynamic web applications by alleviating database load” Ref: http://www.danga.com/memcached/ • Big hash table • Created by Danga Interactive for Live Journal • Signiﬁcantly reduced database load • Perfect for web sites with high database load • In use by Facebook, Twitter, MyYearBook, others 3 : Copyright 2009 Gear6 Inc.

More on Memcached • Takes advantage of available DRAM • Open source • Distributed under BSD license • Server - Current version is 1.4 » http://www.danga.com/memcached/download.bml • Many Clients » http://code.google.com/p/memcached/wiki/Clients 4 : Copyright 2009 Gear6 Inc.

Memcached Server • Limits » Key size = (250 bytes) » 1MB Limit » 32bit/64bit (maximum size of process) • LRU » Least recently accessed items are cycled out » One LRU exists per “slab class” » LRU “evictions” need not be common • Threads? Yes 7 : Copyright 2009 Gear6 Inc.

High Availability • High availability: System design and implementation that ensures a certain absolute degree of operational continuity during a given measurement period. • Organizations » OpenSAF Foundation » SAFourm • HA for Memcache 10 : Copyright 2009 Gear6 Inc.

The case for HA Memcache • What Memcache is NOT: » A persistent data store » A database » Application speciﬁc » Clustered » A large object cache • The intent is if its not in cache hit the DB • Great when your site’s traffic is small • Let’s look at the evolution of a site 12 : Copyright 2009 Gear6 Inc.

Consistent Hashing - Example • PHP – Flexihash – code.google.com/p/ﬂexihash <?php $hash = new Flexihash(); // bulk add $hash->addTargets(array('cache-1', 'cache-2', 'cache-3')); // simple lookup $hash->lookup('object-a'); // "cache-1" $hash->lookup('object-b'); // "cache-2" // add and remove $hash ->addTarget('cache-4') ->removeTarget('cache-1'); // lookup with next-best fallback (for redundant writes) $hash->lookupList('object', 2); // ["cache-2", "cache-4"] // remove cache-2, expect object to hash to cache-4 $hash->removeTarget('cache-2'); $hash->lookup('object'); // "cache-4" 19 : Copyright 2009 Gear6 Inc.

Replication - Repcache Example • Downloaded the memcached-(version)-repcached- (version).tar.gz source and simply compiled it. ./conﬁgure --enable-replication make sudo make install Start two instances of memcached on ports 11211 & 11222 btak@csn07:~/php$ memcached -p 11211 -m 64 -x 127.0.0.1 -v replication: connect (peer=127.0.0.1:11212) replication: marugoto copying replication: close replication: listen btak@csn07:~/php$ memcached -p 11222 -m 64 -x 127.0.0.1 -v replication: connect (peer=127.0.0.1:11212) replication: marugoto copying Replication: start 21 : Copyright 2009 Gear6 Inc.

Replication – Repcache Example Cont Now set and get a value on instance on Connect to port 11222 and try getting port 11211 this value btak@csn07:~$ telnet localhost 11211 btak@csn07:~$ telnet localhost 11222 Trying 127.0.0.1... • Trying 127.0.0.1... Connected to localhost. • Connected to localhost. Escape character is '^]'. • Escape character is '^]'. set hello 0 0 5 • get hello world • VALUE hello 0 5 STORED • world get hello • END VALUE hello 0 5 world END 22 : Copyright 2009 Gear6 Inc.

Replication – Repcache Example Cont Suppose server on 11211 goes down Let’s see if its replicated on 11211 On port 11211 btak@csn07:~$ telnet localhost 11211 Killed Trying 127.0.0.1... btak@csn07:~/php$ memcached -11211 Connected to localhost. -m 64 -x 127.0.0.1 -v Escape character is '^]'. replication: connect get hello (peer=127.0.0.1:11222) VALUE hello 0 5 replication: marugoto copying world replication: start END get key On port 11222 VALUE key 0 5 <---snip myval replication: close END replication: listen replication: accept replication: marugoto start replication: marugoto 2 replication: marugoto owari <---snip--> 23 : Copyright 2009 Gear6 Inc.

About Gear6 • First and leading provider of Memcached solutions • Memcached solution including • High density • High Availability • Advanced memory management • Enhanced reporting capabilities • Support for multi-tenancy • Disruption free software upgrades • 100% client compatible 25 : Copyright 2009 Gear6 Inc.

References • http://dev.mysql.com/doc/mysql-ha-scalability/en/ha-memcached-using- deployment.html • http://dev.mysql.com/doc/mysql-ha-scalability/en/ha-memcached-using- hashtypes.html • http://jayant7k.blogspot.com/2009/04/memcached-replication.html • http://www.lexemetech.com/2007/11/consistent-hashing.html • http://www8.org/w8-papers/2a- webserver/caching/paper2.htmlhttp://www.last.fm/user/RJ/journal/2007/04/10/rz _libketama_-_a_consistent_hashing_algo_for_memcache_clients • http://bazaar.launchpad.net/~libmemcached- developers/libmemcached/trunk/revision/539 26 : Copyright 2009 Gear6 Inc.

Questions? Thank you for attending “Creating High Availability Services for Your Memcached Environment presented” by Gear6 Bill Takacs Gear6 salesinfo@gear6.com +1 650 587 7118 27 : Copyright 2009 Gear6 Inc.

Implementing High Availability Services for Memcached

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