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Whitepaper says about Redis “Redis data structures cannot be horizontally sharded”, p22; but some can

I don’t understand this meaning as it is written the opposite in the same document, p 27:

  • Sharding with Redis

Redis has two categories of data structures: simple keys and counters, and multidimensional sets, lists, and hashes. The bad news is the second category cannot be sharded horizontally. But the good news is that simple keys and counters can.

In the simplest case, you can treat a single Redis node just like a single Memcached node. Just like you might spin up multiple Memcached nodes, you can spin up multiple Redis clusters, and each Redis cluster is responsible for part of the sharded dataset.

page 22

Deploying Redis makes use of familiar concepts such as clusters and nodes. However, Redis has a few important differences compared with Memcached:

• Redis data structures cannot be horizontally sharded. As a result, Redis ElastiCache clusters are always a single node, rather than the multiple nodes we saw with Memcached.

It seems pretty obvious that simple keys and counters at least can be sharded:

https://docs.aws.amazon.com/fr_fr/AmazonElastiCache/latest/red-ug/Shards.html

My question is: am I missing something here?

Thank you!

2 Answers

Hi Guilluame,

Not an answer but have you cross-referenced with the online documentation in English?  I have seen cases were the PDF was outdated or had some lag from the online docs and also where other languages were not updated as frequently or accuracy as the English pages.   I’ve even had to go to the GitHub versions of the AWS docs to get more updated and correct info.

Just a thought.

–Scott

Hello Scott

The whitepaper has been issued this summer (saying it’s not possible)

https://d0.awsstatic.com/whitepapers/performance-at-scale-with-amazon-elasticache.pdf

And the online doc confirms that sharding is possible

https://docs.aws.amazon.com/AmazonElastiCache/latest/red-ug/Shards.html

I’m quite confused…

Scott Pletcher

Might be a case where the AWS Forums for Elasticache could be of help.

John Tucker

Funny, I ran into the same jarring mismatch in documentation. From what I can tell, AWS ElastiCache – Redis can be run in two different modes: Non-Cluster and Cluster. It is in Cluster mode that you get sharding on up to 90 Nodes. https://aws.amazon.com/blogs/database/work-with-cluster-mode-on-amazon-elasticache-for-redis/

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