What is Redis? Checkout the home page, but it is an easy to use and very popular Key-Value Store, w/ PubSub functionality.
It is not meant to replace the C based Redis server, but the goal is to make it feature complete and well performing.
- Testing of server apps (pull up a Redi/S within your Xcode just for testing).
- As an "embedded" database. Redi/S comes as a regular Swift package you can directly embed into your own server or application.
- Easy to extend in a safy language.
Redi/S supports a lot, including PubSub and monitoring.
Redi/S supports a lot not, including transactions or HyperLogLogs.
There is a list of supported commands.
Contributions welcome!! A lot of the missing stuff is really easy to add!
Performance differs, e.g. lists are implemented using arrays (hence RPUSH is okayish, LPUSH is very slow). But looking at just the simple GET/SET, it is surprisingly close to the highly optimized C implementation:
Redi/S (2 NIO threads on MacPro 3,7 GHz Quad-Core Intel Xeon E5):
helge@ZeaPro ~ $ redis-benchmark -p 1337 -t SET,GET,RPUSH,INCR -n 500000 -q SET: 48003.07 requests per second GET: 48459.00 requests per second INCR: 43890.45 requests per second RPUSH: 46087.20 requests per second
Redis 4.0.8 (same MacPro 3,7 GHz Quad-Core Intel Xeon E5):
helge@ZeaPro ~ $ redis-benchmark -t SET,GET,RPUSH,INCR -n 500000 -q SET: 54884.74 requests per second GET: 54442.51 requests per second INCR: 54692.62 requests per second RPUSH: 54013.18 requests per second
There are Performance notes, looking at the specific NIO implementation of Redi/S.
Persistence is really inefficient, the databases are just dumped as JSON via Codable. Easy to fix.
How to run
$ swift build -c release $ .build/release/redi-s 2383:M 11 Apr 17:04:16.296 # sSZSsSZSsSZSs Redi/S is starting sSZSsSZSsSZSs 2383:M 11 Apr 17:04:16.302 # Redi/S bits=64, pid=2383, just started 2383:M 11 Apr 17:04:16.303 # Configuration loaded ____ _ _ ______ | _ \ ___ __| (_) / / ___| Redi/S 64 bit | |_) / _ \/ _` | | / /\___ \ | _ < __/ (_| | |/ / ___) | Port: 1337 |_| \_\___|\__,_|_/_/ |____/ PID: 2383 2383:M 11 Apr 17:04:16.304 # Server initialized 2383:M 11 Apr 17:04:16.305 * Ready to accept connections
There are a few inefficiencies, the worst being the persistent storage. Yet generally this seems to work fine.
The implementation has grown a bit and could use a little refactoring, specially the database dump parts.
Playing with the Server
You'd like to play with this, but never used Redis before? OK, a small tutorial on what you can do with it.
First make sure the server runs in one shell:
$ swift build -c release $ .build/release/redi-s 83904:M 12 Apr 16:33:15.159 # sSZSsSZSsSZSs Redi/S is starting sSZSsSZSsSZSs 83904:M 12 Apr 16:33:15.169 # Redi/S bits=64, pid=83904, just started 83904:M 12 Apr 16:33:15.170 # Configuration loaded ____ _ _ ______ | _ \ ___ __| (_) / / ___| Redi/S 64 bit | |_) / _ \/ _` | | / /\___ \ | _ < __/ (_| | |/ / ___) | Port: 1337 |_| \_\___|\__,_|_/_/ |____/ PID: 83904 83904:M 12 Apr 16:33:15.176 # Server initialized 83904:M 12 Apr 16:33:15.178 * Ready to accept connections
Notice how the server says: "Port 1337". This is the port the server is running on.
You can directly connect to the server and issue Redis commands (the server is then running the connection in
telnet mode, which is different to the regular RESP protocol):
$ nc localhost 1337 KEYS * *0 SET theanswer 42 +OK GET theanswer $2 42
Redis is a key/value store. That is, it acts like a big Dictionary that can be modified from multiple processes. Above we list the available
KEYS, then we set the key
theanswer to the value 42, and retrieve it. (Redis provides great documentation on the available commands, Redi/S implements many, but not all of them).
Redis provides a tool called
redis-cli, which is a much more convenient way to access the server. On macOS you can install that using
brew install redis (which also gives you the real server), on Ubuntu you can grab it via
sudo apt-get install redis-tools.
The same thing we did in
$ redis-cli -p 1337 127.0.0.1:1337> KEYS * 1) "theanswer" 127.0.0.1:1337> SET theanswer 42 OK 127.0.0.1:1337> GET theanswer "42"
Redis is particularily useful for HTTP session stores, and for caches. When setting a key, you can set an "expiration" (in seconds, milliseconds, or Unix timestamps):
127.0.0.1:1337> EXPIRE theanswer 10 (integer) 1 127.0.0.1:1337> TTL theanswer (integer) 6 127.0.0.1:1337> GET theanswer "42" 127.0.0.1:1337> TTL theanswer (integer) -2 127.0.0.1:1337> GET theanswer (nil)
We are using "strings" here. In Redis "strings" are actually "Data" objects, i.e. binary arrays of bytes (this is even true for bytes!). For example in a web application, you could use the "session-id" you generate, serialize your session into a Data object, and then store it like
SET session-id <session> TTL 600.
But how do we generate keys (e.g. session-ids) in a distributed setting? As usual there are many ways to do this. For example you could use a Redis integer key which provides atomic increment and decrement operations:
127.0.0.1:1337> SET idsequence 0 OK 127.0.0.1:1337> INCR idsequence (integer) 1 127.0.0.1:1337> INCR idsequence (integer) 2
Or if you generate keys on the client side, you can validate that they are unique using SETNX. For example:
127.0.0.1:1337> SETNX mykey 10 (integer) 1
And another client will get
127.0.0.1:1337> SETNX mykey 10 (integer) 0
Redis cannot only store string (read: Data) values, it can also store lists, sets and hashes (dictionaries). As well as some other datatypes: Data Types Intro.
127.0.0.1:1337> RPUSH chatchannel "Hi guys!" (integer) 1 127.0.0.1:1337> RPUSH chatchannel "How is it going?" (integer) 2 127.0.0.1:1337> LLEN chatchannel (integer) 2 127.0.0.1:1337> LRANGE chatchannel 0 -1 1) "Hi guys!" 2) "How is it going?" 127.0.0.1:1337> RPOP chatchannel "How is it going?" 127.0.0.1:1337> RPOP chatchannel "Hi guys!" 127.0.0.1:1337> RPOP chatchannel (nil)
Assume you want to debug what's going on on your Redis server. You can do this by connecting w/ a fresh client and put that into "monitoring" mode. The Redis server will echo all commands it receives to that monitor:
$ redis-cli -p 1337 127.0.0.1:1337> MONITOR OK
Some other client:
127.0.0.1:1337> hmset user:1000 username antirez birthyear 1976 verified 1 OK 127.0.0.1:1337> hmget user:1000 username verified 1) "antirez" 2) "1"
The monitor will print:
1523545069.071390 [0 127.0.0.1:60904] "hmset" "user:1000" "username" "antirez" "birthyear" "1976" "verified" "1" 1523545087.016070 [0 127.0.0.1:60904] "hmget" "user:1000" "username" "verified"
Redis includes a simple publish/subscribe server. Any numbers of clients can subscribe to any numbers of channels. Other clients can then push "messages" to a channel, and all subscribed clients will receive them.
127.0.0.1:1337> PSUBSCRIBE thermostats* Reading messages... (press Ctrl-C to quit) 1) psubscribe 2) "thermostats*" 3) (integer) 1
Another client (the reply contains the number of consumers):
127.0.0.1:1337> PUBLISH thermostats:kitchen "temperature set to 42℃" (integer) 1
The subscribed client will get:
1) message 2) "thermostats:kitchen" 3) "temperatur set to 4242℃"
Note: PubSub is separate to the key-value store. You cannot watch keys using that! (there are blocking list operations for producer/consumer scenarios, but those are not yet supported by Redi/S)
Redis tools also include a tool called
redis-benchmark which can be, similar to
wrk be used to measure the server performance.
For example, to exercise the server with half a million SET, GET, RPUSH and INCR requests each:
$ redis-benchmark -p 1337 -t SET,GET,RPUSH,INCR -n 500000 -q SET: 43192.81 requests per second GET: 46253.47 requests per second INCR: 38952.95 requests per second RPUSH: 39305.09 requests per second
There is a
#swift-nio channel on the swift-server Slack.