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KeyDB is a high performance fork of Redis with a focus on multithreading, memory efficiency, and high throughput. In addition to multithreading, KeyDB also has features only available in Redis Enterprise such as [Active Replication](https://github.com/JohnSully/KeyDB/wiki/Active-Replication), [FLASH storage](https://github.com/JohnSully/KeyDB/wiki/FLASH-Storage) support, and some not available at all such as direct backup to AWS S3.
KeyDB maintains full compatibility with the Redis protocol, modules, and scripts. This includes the atomicity guarantees for scripts and transactions. Because KeyDB keeps in sync with Redis development KeyDB is a superset of Redis functionality, making KeyDB a drop in replacement for existing Redis deployments.
On the same hardware KeyDB can perform twice as many queries per second as Redis, with 60% lower latency. Active-Replication simplifies hot-spare failover allowing you to easily distribute writes over replicas and use simple TCP based load balancing/failover. KeyDB's higher performance allows you to do more on less hardware which reduces operation costs and complexity.
KeyDB has a different philosophy on how the codebase should evolve. We feel that ease of use, high performance, and a "batteries included" approach is the best way to create a good user experience. While we have great respect for the Redis maintainers it is our opinion that the Redis approach focuses too much on simplicity of the code base at the expense of complexity for the user. This results in the need for external components and workarounds to solve common problems - resulting in more complexity overall.
Because of this difference of opinion features which are right for KeyDB may not be appropriate for Redis. A fork allows us to explore this new development path and implement features which may never be a part of Redis. KeyDB keeps in sync with upstream Redis changes, and where applicable we upstream bug fixes and changes. It is our hope that the two projects can continue to grow and learn from each other.
Please note keydb-benchmark and redis-benchmark are currently single threaded and too slow to properly benchmark KeyDB. We recommend using a redis cluster benchmark tool such as [memtier](https://github.com/RedisLabs/memtier_benchmark). Please ensure your machine has enough cores for both KeyDB and memteir if testing locally. KeyDB expects exclusive use of any cores assigned to it.
For more details on how we benchmarked KeyDB along with performance numbers check out our blog post: [Redis Should Be Multithreaded](https://medium.com/@john_63123/redis-should-be-multi-threaded-e28319cab744?source=friends_link&sk=7ce8e9fe3ec8224a4d27ef075d085457)
The number of threads used to serve requests. This should be related to the number of queues available in your network hardware, *not* the number of cores on your machine. Because KeyDB uses spinlocks to reduce latency; making this too high will reduce performance. We recommend using 4 here. By default this is set to one.
If you would like to use the [FLASH backed](https://github.com/JohnSully/KeyDB/wiki/FLASH-Storage) storage this option configures the directory for KeyDB's temporary files. This feature relies on snapshotting to work so must be used on a BTRFS filesystem. ZFS may also work but is untested. With this feature KeyDB will use RAM as a cache and page to disk as necessary. NOTE: This requires special compilation options, see Building KeyDB below.
If you would like KeyDB to dump and load directly to AWS S3 this option specifies the bucket. Using this option with the traditional RDB options will result in KeyDB backing up twice to both locations. If both are specified KeyDB will first attempt to load from the local dump file and if that fails load from S3. This requires the AWS CLI tools to be installed and configured which are used under the hood to transfer the data.
If you are using active-active replication set `active-replica` option to “yes”. This will enable both instances to accept reads and writes while remaining synced. [Click here](https://docs.keydb.dev/docs/active-rep/) to see more on active-rep in our docs section. There are also [docker examples]( https://docs.keydb.dev/docs/docker-active-rep/) on docs.
KeyDB can be compiled and is tested for use on Linux. KeyDB currently relies on SO_REUSEPORT's load balancing behavior which is available only in Linux. When we support marshalling connections across threads we plan to support other operating systems such as FreeBSD.
KeyDB works by running the normal Redis event loop on multiple threads. Network IO, and query parsing are done concurrently. Each connection is assigned a thread on accept(). Access to the core hash table is guarded by spinlock. Because the hashtable access is extremely fast this lock has low contention. Transactions hold the lock for the duration of the EXEC command. Modules work in concert with the GIL which is only acquired when all server threads are paused. This maintains the atomicity guarantees modules expect.
Unlike most databases the core data structure is the fastest part of the system. Most of the query time comes from parsing the REPL protocol and copying data to/from the network.
Future work:
- Allow rebalancing of connections to different threads after the connection
- Allow multiple readers access to the hashtable concurrently
If you are looking to enable flash support with the build (make MALLOC=memkind) then use the following command:
```
$ docker run -it --rm -v /path-to-dump-binaries:/keydb_bin eqalpha/keydb-build-bin:flash
```
Please note that you will need libcurl4-openssl-dev in order to run keydb. With flash version you may need libnuma-dev and libtool installed in order to run the binaries. Keep this in mind especially when running in a container. For a copy of all our Dockerfiles, please see them on [docs]( https://docs.keydb.dev/docs/dockerfiles/).
