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Lightning fast NoSQL with Spring Data Redis

Dr. Xinyu Liu | May 25, 2016
6 uses cases for Redis in server-side Java applications

As an example, consider seller inventory in an auction website. When a buyer tries to buy an item from a seller, you watch for changes on the seller's inventory inside the Redis transaction. In the meantime, you remove the item from the same inventory. Before the transaction closes, if the inventory was touched by more than one process (for instance, if two buyers purchased the same item at the same moment), the transaction will roll back; otherwise, the transaction will commit. A retry can kick in after a rollback.

A transaction pitfall in Spring Data Redis

I learned a hard lesson when enabling Redis transactions in the Spring RedisTemplate class redisTemplate.setEnableTransactionSupport(true);: Redis started returning junk data after running for a few days, causing serious data corruption. A similar case was reported on StackOverflow.

By running a monitor command, my team discovered that after a Redis operation or RedisCallback, Spring doesn't close the Redis connection automatically, as it should do. Reusing an unclosed connection may return junk data from an unexpected key in Redis. Interestingly, this issue doesn't show up when transaction support is set to false in RedisTemplate.

We discovered that we could make Spring close Redis connections automatically by configuring a PlatformTransactionManager (such as DataSourceTransactionManager) in the Spring context, then using the @Transactional annotation to declare the scope of Redis transactions.

Based on this experience, we believe it's good practice to configure two separate RedisTemplates in the Spring context: One with transaction set to false is used on most Redis operations; the other with transaction enabled is only applied to Redis transactions. Of course PlatformTransactionManager and @Transactional must be declared to prevent junk values from being returned.

Moreover, we learned the downside of mixing a Redis transaction with a relational database transaction, in this case JDBC. Mixed transactions do not behave as you would expect.

Conclusion

With this article I've hoped to introduce other Java enterprise developers to the power of Redis, particularly when used as a remote data cache and for volatile data. I've introduced six effective uses cases for Redis, shared a few performance optimizing techniques, and explained how my team at Glu Mobile worked around getting junk data as a result of mis-configured transactions in Spring Data Redis. I hope that this article has piqued your curiosity about Redis NoSQL and offered some pathways for exploring it in your own Java EE systems.

 

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