Redis for .NET Developer – Redis Transactions

Redis

Redis Transactions

Redis provides a way to do Transactions, but the transactions are somewhat different than what you know from a SQL Relational Database perspective. In SQL Relation Database world you can executed partially and then rolled back the entire transaction. While Redis uses the MULTI and EXEC commands where every command passed as part of a transaction is executed one after another until they have all completed and only after they have completed then other clients may execute their commands. You can think of it more like a queue that stores all your commands and when you call EXEC it loops through the queue and execute the task on the queue one after the other while being locked in the loop i,e no other thread could come in.

Below is an example of a Client queuing up the calls to Redis using MULTI in Redis client library to make a call to Redis Server to process the commands in an EXEC.

redis-transaction

Note: You see Client2 also making a call to Redis but the command is only executed after the process of Client commands.

One important thing to note is when using Redis Transaction one cannot make decisions inside the block, but you can use WATCH to prevent a key to be changed in a transaction. E.g We can WATCH the key “A” in our sample and when we try to use it in MULTI and EXEC it will fail to change A. A will be discarded as shown below, when A was set as 4, even inside of the block we were not able to make the change the EXEC was in some way ROLLBACKED i.e DISCARD

127.0.0.1:6379> WATCH A
OK
127.0.0.1:6379> INCR A
(integer) 4
127.0.0.1:6379> GET A
"4"
127.0.0.1:6379> MULTI
OK
127.0.0.1:6379> INCR A
QUEUED
127.0.0.1:6379> EXEC
(nil)
127.0.0.1:6379>
127.0.0.1:6379> GET A
"4"

In Redis StackExchange library uses Conditions to mimic Watch since Redis StackExchange uses Multiplex. Commands can come in different stages but conditions can be used to detect changes.

C# code using Redis Transactions

 class Program
    {
        static void Main(string[] args)
        {
            var redis = RedisStore.RedisCache;

            RedisKey alphaKey = "alphaKey";
            RedisKey betaKey = "betaKey";
            RedisKey gammaKey = "gammaKey";

            redis.KeyDelete(alphaKey, CommandFlags.FireAndForget);
            redis.KeyDelete(betaKey, CommandFlags.FireAndForget);
            redis.KeyDelete(gammaKey, CommandFlags.FireAndForget);

            var trans = redis.CreateTransaction();

            var incr = trans.StringSetAsync(alphaKey, "abc");
            var exec = trans.ExecuteAsync();

            var result = redis.Wait(exec);
            var alphaValue = redis.StringGet(alphaKey);

            Console.WriteLine($"Alpha key is {alphaValue} and result is {result}");
            
            //using conditions to watch keys
            var condition = trans.AddCondition(Condition.KeyNotExists(gammaKey));
            var keyIncrement = trans.StringIncrementAsync(gammaKey);
            exec = trans.ExecuteAsync();
            result = redis.Wait(exec);

            var gammaValue = redis.StringGet(gammaKey);

            Console.WriteLine($"Gamma key is {gammaValue} and result is {result}");

            //fail condition
            condition = trans.AddCondition(Condition.KeyNotExists(gammaKey));
            keyIncrement = trans.StringIncrementAsync(gammaKey);
            exec = trans.ExecuteAsync();

            //resultis false 
            result = redis.Wait(exec);

            gammaValue = redis.StringGet(gammaKey);

            //value is still 1 and result is false
            Console.WriteLine($"Gamma key is {gammaValue} and result is {result}");

            Console.ReadKey();
        }
    }

So this covers the basic usage of Redis Transactions, in the next blog post I will cover how to use Lua in Redis.

For the code please visit
https://github.com/taswar/RedisForNetDevelopers/tree/master/11.RedisTransaction

For previous Redis topics

Xamarin Dev Days »

« Redis for .NET Developers – Redis Pipeline Batching

Categories: C# Redis

Tags: C#redisStackExchange.Redis

Taswar Bhatti:

Redis Transactions

C# code using Redis Transactions

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