Is Redis thread safe?

Asked By: Alesha Manrique | Last Updated: 1st March, 2020
Category: technology and computing databases
4/5 (922 Views . 28 Votes)
Enter the Redis GIL
Luckily, Salvatore Sanfilippo has added a revolutionary change just near the finish line of Redis 4.0 and the release of the modules API : Thread Safe Contexts and the Global Lock. The idea is simple. While Redis still remains single threaded, a module can run many threads.

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Similarly, is Redis Cache thread safe?

Redis is single-threaded. As such all commands in Redis are atomic. However, depending on the implementation in the client library sharing a connection may still be problematic. For this reason, among others, your client access needs be be thread safe.

Also Know, is Redis concurrent? OK, Redis is single-threaded at user-level, OTOH, all asynchronous I/O is supported by kernel thread pools and/or split-level drivers. 'Concurrent', to some, includes distributing network events to socket state-machines.

In this regard, is Redis single threaded?

Redis is, mostly, a single-threaded server from the POV of commands execution (actually modern versions of Redis use threads for different things). It is not designed to benefit from multiple CPU cores. People are supposed to launch several Redis instances to scale out on several cores if needed.

How do I optimize Redis?

To summarize:

  1. Do set a maxmemory limit.
  2. Do use allkeys-lru policies for dedicated cache instances. Let Redis manage key eviction by itself.
  3. Do not set expire for keys, it adds additional memory overhead per key.
  4. Do tune the precision of the LRU algorithm to favor speed over accuracy.

34 Related Question Answers Found

Is Redis a cache?

Redis is an open source (BSD licensed), in-memory data structure store, used as a database, cache and message broker. It supports data structures such as strings, hashes, lists, sets, sorted sets with range queries, bitmaps, hyperloglogs, geospatial indexes with radius queries and streams.

Is Redis atomic?

All commands in a transaction are sequentially executed as a single isolated operation. It is not possible that a request issued by another client is served in the middle of the execution of a Redis transaction. Redis transaction is also atomic. Atomic means either all of the commands or none are processed.

Why Redis is single threaded?

Because it is a single thread, only one operation is in place at the same time, so time-consuming commands can cause concurrency to degrade, not just read concurrency, but write concurrency will also degrade.

When should you not use Redis?

We will not want to use Redis for use cases like these:
  1. Storing large amounts of data in a single string value (e.g. the most recent feed contents for each user).
  2. Storing data across two or more dimensions (e.g. a score for each (user, topic) pair).
  3. Storing data that requires queries with high time complexity.

Why is Redis so fast?

The ability to work with different types of data is what really makes Redis an especially powerful tool. A key value could be just a string as is used with Memcached. All of the data is stored in RAM, so the speed of this system is phenomenal, often performing even better than Memcached.

What happens if Redis runs out of memory?

What happens if Redis runs out of memory? If this limit is reached Redis will start to reply with an error to write commands (but will continue to accept read-only commands), or you can configure it to evict keys when the max memory limit is reached in the case where you are using Redis for caching.

Does Redis support SQL?

You cann't use SQL in Redis because it is a memory Database, which unlike most of relational Databases. Please check the documention, that will help you to use it.

Does Redis keep all data in memory?

Redis is an in-memory database because it keeps the whole data set in memory, and answers all queries from memory. Because RAM is faster than disks, this means Redis always has very fast reads. They always keep the whole data set including indices on disk in a format that allows random access.

Is Redis a NoSQL DB?


The short answer is yes. Redis is an open source (BSD licensed), in-memory data structure store. There are actually 4 different kinds of NoSQL database types, which include: Key-value stores are the most simple among NoSQL Databases.

Is Redis in memory?

Redis is an In-Memory Database(IMDB) as it relies on main memory of computer for data storage while others use Disk Storage database mechanism. That is why Redis is faster than disk-optimized databases because disk access is slower than memory access. For performance it keeps and store data in memory.

Is Redis faster than MySQL?

Introduction to Redis
Actually, Redis is an advanced key-value store. It is super fast with amazingly high throughput, as it can perform approximately 110000 SETs per second, about 81000 GETs per second. In this article, to have some benchmarks in comparison to MySQL, we will be using Redis as a caching engine only.

How many clients can Redis handle?

Maximum number of clients
In Redis 2.6 this limit is dynamic: by default it is set to 10000 clients, unless otherwise stated by the maxclients directive in Redis. conf. However, Redis checks with the kernel what is the maximum number of file descriptors that we are able to open (the soft limit is checked).

When should I use Redis?

Top 5 Redis Use Cases
  1. Session Cache. One of the most apparent use cases for Redis is using it as a session cache.
  2. Full Page Cache (FPC) Outside of your basic session tokens, Redis provides a very easy FPC platform to operate in.
  3. Queues.
  4. Leaderboards/Counting.
  5. Pub/Sub.
  6. More Redis Resources.

How reliable is Redis?


Redis is actually a very reliable engine to store data, as long as you keep in mind its design principles. A Redis instance (non-sharded) can handle 50 times that in a single thread, while maintaining sub-ms latency.

Who uses Redis in production?

Who uses Redis? 4502 companies reportedly use Redis in their tech stacks, including Airbnb, Uber, and Instagram. 12681 developers on StackShare have stated that they use Redis.

How many requests per second can Redis handle?

As previously measured, a benchmark setting 100 Bytes values for each key in Redis, would be hard limited by the network at around 32 million queries per second per VM. Even for 1000 Bytes values, Redis would only be hard limited by the network at around 3 million queries per second per VM.