Amazon ElastiCache for Redis
ElastiCache for Redis User Guide (API Version 2015-02-02)

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Common ElastiCache Use Cases and How ElastiCache Can Help

Whether serving the latest news, a top-10 leaderboard, a product catalog, or selling tickets to an event, speed is the name of the game. The success of your website and business is greatly affected by the speed at which you deliver content.

In "For Impatient Web Users, an Eye Blink Is Just Too Long to Wait," the New York Times noted that users can register a 250-millisecond (1/4 second) difference between competing sites. Users tend to opt out of the slower site in favor of the faster site. Tests done at Amazon, cited in How Webpage Load Time Is Related to Visitor Loss, revealed that for every 100-ms (1/10 second) increase in load time, sales decrease 1 percent.

If someone wants data, you can deliver that data much faster if it's cached. That's true whether it's for a webpage or a report that drives business decisions. Can your business afford to not cache your webpages so as to deliver them with the shortest latency possible?

It might seem intuitively obvious that you want to cache your most heavily requested items. But why not cache your less frequently requested items? Even the most optimized database query or remote API call is noticeably slower than retrieving a flat key from an in-memory cache. Noticeably slower tends to send customers elsewhere.

The following examples illustrate some of the ways using ElastiCache can improve overall performance of your application.

In-Memory Data Store

The primary purpose of an in-memory key-value store is to provide ultrafast (submillisecond latency) and inexpensive access to copies of data. Most data stores have areas of data that are frequently accessed but seldom updated. Additionally, querying a database is always slower and more expensive than locating a key in a key-value pair cache. Some database queries are especially expensive to perform. An example is queries that involve joins across multiple tables or queries with intensive calculations. By caching such query results, you pay the price of the query only once. Then you can quickly retrieve the data multiple times without having to re-execute the query.

The following image shows ElastiCache caching.


				Image: ElastiCache Caching

What Should I Cache?

When deciding what data to cache, consider these factors:

Speed and expense – It's always slower and more expensive to get data from a database than from a cache. Some database queries are inherently slower and more expensive than others. For example, queries that perform joins on multiple tables are much slower and more expensive than simple, single table queries. If the interesting data requires a slow and expensive query to get, it's a candidate for caching. If getting the data requires a relatively quick and simple query, it might still be a candidate for caching, depending on other factors.

Data and access pattern – Determining what to cache also involves understanding the data itself and its access patterns. For example, it doesn't make sense to cache data that changes quickly or is seldom accessed. For caching to provide a real benefit, the data should be relatively static and frequently accessed. An example is a personal profile on a social media site. On the other hand, you don't want to cache data if caching it provides no speed or cost advantage. For example, it doesn't make sense to cache webpages that return search results because the queries and results are usually unique.

Staleness – By definition, cached data is stale data. Even if in certain circumstances it isn't stale, it should always be considered and treated as stale. To tell whether your data is a candidate for caching, determine your application's tolerance for stale data.

Your application might be able to tolerate stale data in one context, but not another. For example, suppose that your site serves a publicly traded stock price. Your customers might accept some staleness with a disclaimer that prices might be n minutes delayed. But if you serve that stock price to a broker making a sale or purchase, you want real-time data.

Consider caching your data if the following is true:

  • Your data is slow or expensive to get when compared to cache retrieval.

  • Users access your data often.

  • Your data stays relatively the same, or if it changes quickly staleness is not a large issue.

For more information, see the following:

Gaming Leaderboards (Redis Sorted Sets)

Redis sorted sets move the computational complexity of leaderboards from your application to your Redis cluster.

Leaderboards, such as the top 10 scores for a game, are computationally complex. This is especially true when there is a large number of concurrent players and continually changing scores. Redis sorted sets guarantee both uniqueness and element ordering. Using Redis sorted sets, each time a new element is added to the sorted set it's reranked in real time. It's then added to the set in its correct numeric order.

In the following diagram, you can see how an ElastiCache for Redis gaming leaderboard works.

Image: ElastiCache for Redis Gaming leaderboard diagram

Example - Redis Leaderboard

In this example, four gamers and their scores are entered into a sorted list using ZADD. The command ZREVRANGEBYSCORE lists the players by their score, high to low. Next, ZADD is used to update June's score by overwriting the existing entry. Finally, ZREVRANGEBYSCORE lists the players by their score, high to low. The list shows that June has moved up in the rankings.

ZADD leaderboard 132 Robert ZADD leaderboard 231 Sandra ZADD leaderboard 32 June ZADD leaderboard 381 Adam ZREVRANGEBYSCORE leaderboard +inf -inf 1) Adam 2) Sandra 3) Robert 4) June ZADD leaderboard 232 June ZREVRANGEBYSCORE leaderboard +inf -inf 1) Adam 2) June 3) Sandra 4) Robert

The following command tells June where she ranks among all the players. Because ranking is zero-based, ZREVRANK returns a 1 for June, who is in second position.

ZREVRANK leaderboard June 1

For more information, see the Redis documentation about sorted sets.

Messaging (Redis Pub/Sub)

When you send an email message, you send it to one or more specified recipients. In the pub/sub paradigm, you send a message to a specific channel not knowing who, if anyone, receives it. The people who get the message are those who are subscribed to the channel. For example, suppose that you subscribe to the news.sports.golf channel. You and all others subscribed to the news.sports.golf channel get any messages published to news.sports.golf.

Redis pub/sub functionality has no relation to any key space. Therefore, it doesn't interfere on any level. In the following diagram, you can find an illustration of ElastiCache for Redis messaging.

Image: ElastiCache for Redis messaging diagram

Subscribing

To receive messages on a channel, you subscribe to the channel. You can subscribe to a single channel, multiple specified channels, or all channels that match a pattern. To cancel a subscription, you unsubscribe from the channel specified when you subscribed to it. Or, if you subscribed using pattern matching, you unsubscribe using the same pattern that you used before.

Example - Subscription to a Single Channel

To subscribe to a single channel, use the SUBSCRIBE command specifying the channel you want to subscribe to. In the following example, a client subscribes to the news.sports.golf channel.

SUBSCRIBE news.sports.golf

After a while, the client cancels their subscription to the channel using the UNSUBSCRIBE command specifying the channel to unsubscribe from.

UNSUBSCRIBE news.sports.golf

Example - Subscriptions to Multiple Specified Channels

To subscribe to multiple specific channels, list the channels with the SUBSCRIBE command. In the following example, a client subscribes to the news.sports.golf, news.sports.soccer, and news.sports.skiing channels.

SUBSCRIBE news.sports.golf news.sports.soccer news.sports.skiing

To cancel a subscription to a specific channel, use the UNSUBSCRIBE command and specify the channel to unsubscribe from.

UNSUBSCRIBE news.sports.golf

To cancel subscriptions to multiple channels, use the UNSUBSCRIBE command and specify the channels to unsubscribe from.

UNSUBSCRIBE news.sports.golf news.sports.soccer

To cancel all subscriptions, use UNSUBSCRIBE and specify each channel. Or use UNSUBSCRIBE and don't specify a channel.

UNSUBSCRIBE news.sports.golf news.sports.soccer news.sports.skiing

or

UNSUBSCRIBE

Example - Subscriptions Using Pattern Matching

Clients can subscribe to all channels that match a pattern by using the PSUBSCRIBE command.

In the following example, a client subscribes to all sports channels. You don't list all the sports channels individually, as you do using SUBSCRIBE. Instead, with the PSUBSCRIBE command you use pattern matching.

PSUBSCRIBE news.sports.*

Example Canceling Subscriptions

To cancel subscriptions to these channels, use the PUNSUBSCRIBE command.

PUNSUBSCRIBE news.sports.*

Important

The channel string sent to a [P]SUBSCRIBE command and to the [P]UNSUBSCRIBE command must match. You can't PSUBSCRIBE to news.* and PUNSUBSCRIBE from news.sports.* or UNSUBSCRIBE from news.sports.golf.

Publishing

To send a message to all subscribers to a channel, use the PUBLISH command, specifying the channel and the message. The following example publishes the message, "It’s Saturday and sunny. I’m headed to the links." to the news.sports.golf channel.

PUBLISH news.sports.golf "It's Saturday and sunny. I'm headed to the links."

A client can"t publish to a channel that it's subscribed to.

For more information, see Pub/Sub in the Redis documentation.

Recommendation Data (Redis Hashes)

Using INCR or DECR in Redis makes compiling recommendations simple. Each time a user "likes" a product, you increment an item:productID:like counter. Each time a user "dislikes" a product, you increment an item:productID:dislike counter. Using Redis hashes, you can also maintain a list of everyone who has liked or disliked a product. The following diagram illustrates an ElastiCache for Redis real-time analytics store.

Image: ElastiCache for Redis real-time analytics store

Example - Likes and Dislikes

INCR item:38923:likes HSET item:38923:ratings Susan 1 INCR item:38923:dislikes HSET item:38923:ratings Tommy -1

Other Redis Uses

The blog post How to take advantage of Redis just adding it to your stack by Salvatore Sanfilippo discusses a number of common database concerns and how they can be easily solved using Redis. This approach removes load from your database and improves performance.

ElastiCache Customer Testimonials

To learn about how businesses like Airbnb, PBS, Esri, and others use Amazon ElastiCache to grow their businesses with improved customer experience, see How Others Use Amazon ElastiCache.

You can also watch the ElastiCache Videos for additional ElastiCache customer use cases.