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On Redis. Interview with Salvatore Sanfilippo

by Roberto V. Zicari on November 7, 2019

“I think Redis is entering a new stage where there are a number of persons that now actively daily contribute to the open source. It’s not just “mostly myself”, and that’s great.” –Salvatore Sanfilippo

I have interviewed Salvatore Sanfilippo, the original developer of Redis. Redis is an open source in-memory database that persists on disk.

Q1.What is new in the Redis 6 release?

Salvatore Sanfilippo: The main new features are ACLs, SSL, I/O threading, the new protocol called RESP3, assisted client side caching support, a ton of new modules capabilities, new cluster tools, diskless replication, and other things, a very long list indeed.

Q2.Can you tell us a bit more about the new version of the Redis protocol (RESP3), what is it?  and why is it important?

Salvatore Sanfilippo: It’s just an incremental improvement over RESP2. The main goal is to make it more semantical. RESP2 is only able to represent arrays from the point of view of aggregated data types. Instead with RESP3 we have sets, hashes, and so forth. This makes simpler for client libraries to understand how to report the command reply back to the client, without having a conversion table from the array to the library language target type.

Q3.You have recently implemented a client side caching for Redis 6. What are the main benefits of this?

Salvatore Sanfilippo: Most big shops using Redis end having some way to memorize some information directly into the client. Imagine a social network that caches things in Redis, where the same post is displayed so many times because it is about a very famous person. To fetch it every time from Redis is a lot of useless efforts and cache traffic. So many inevitably end creating protocols to retain very popular items directly in the memory of the front-end systems, inside the application memory space. To do that you need to handle the invalidation of the cached keys. Redis new client side caching is a server side “help” in order to accomplish this goal. It is able to track what keys a given client memorized, and inform it when such keys gets modified, so that the client can invalidate them.

Q4. Are there any drawbacks as well?

Salvatore Sanfilippo: Sure, more caching layers, more invalidation, more complexity. Also more memory used by Redis to track the client keys.

Q5. “Streams” data structure were introduced in Redis 5. What is it? How does it differ from other open source streaming framework such as Apache Pulsar or Kafka ?

Salvatore Sanfilippo: A Redis stream is basically a “log” of items, where each item is a small dictionary composed of keys and values. On top of that simple data structure, which is very very memory efficient, we do other things that are more messaging and less data structure: consume a stream via a consumer group, block for new messages, and so forth.
There are use cases that can be solved with both Redis Streams and Pulsar or Kafka, but I’m against products comparisons, it’s up the users to understand what they need.

Q6.What are you working at present?

Salvatore Sanfilippo: At finalizing the Redis 6 release adding many new module APIs, and also porting the Disque project ( as a Redis module.

Q7. What is your vision ahead for Redis?

Salvatore Sanfilippo: I think Redis is entering a new stage where there are a number of persons that now actively daily contribute to the open source. It’s not just “mostly myself”, and that’s great.
Redis modules are playing an interesting role, we see Redis Labs creating modules, but also from the bug reports in the Github repository, I think that there are people that are writing modules to specialize Redis for their own uses, which is great.


 Salvatore Sanfilippo


Salvatore started his career in 1997 as a security researcher, writing the hping ( security tool and inventing the Idle Scan ( Later he worked on embedded systems, focusing on programming languages research and creating a small footprint Tcl interpreter, which is still in active development. With a colleague, Salvatore created the first two Italian social applications in partnership with Telecom Italia. After this experience, he decided to explore new ways to improve web app development, and ended up writing the first alpha version of Redis and open sourcing it. Since 2009, he has dedicated most of his time to developing Redis open source code.

Over the years, Salvatore has also created a number of other open source projects ranging from software defined radio, to line editing tools, to children development environments. He lives in Sicily, Italy.


Redis is an open source (BSD licensed), in-memory data structure store, used as a database, cache and message broker.

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