linearkeyallocator's Introduction

LinearKeyAllocator

LinearKeyAllocator allows to generate incremental keys (int, long) based on last seed value stored in database.

Works likes the HiLo algorithm (from NHibernate) but better becouse do not create big holes when application restarts.

It aims to be a tool for generating database keys without having to rely on RDBMS identity column.

LinearKeyAllocator works like database 'Sequence'. It means does not attach to any ambient transaction.

Once generated chunk of keys are available until application restarts. After restart it will start from last saved max value.

Why is it better than HiLo?

Set LinearKeyAllocator seedSize to 20.

LinearKeyAllocator          HiLo
...
100                         65536
101                         65537
102                         65538
... application restart
120                         131072
121                         131073
122                         131073
... application restart
140                         196608

Example

class Program
{
    private static string cnn =
        "Server=(local); Database=Test; Trusted_Connection=True; MultipleActiveResultSets=true";

    static async Task Main(string[] args)
    {
        var generator = await new KeyAllocator(cnn).Initialize();

        const string type1 = "Type1";
        const string type2 = "Type2";

        using var scope =
            new TransactionScope(
                TransactionScopeOption.Required,
                TransactionScopeAsyncFlowOption.Enabled);

        for (var i = 0; i < 5000; i++)
        {
            var key = (i % 2 == 0) ? type1 : type2;

            var value = await generator.GenerateInt32(key);
            Console.WriteLine("{0}: {1}", key, value);
        }

        scope.Complete();

        Console.WriteLine("Press any key...");
        Console.ReadKey();
    }
}

Sql Script

CREATE TABLE [dbo].[LinearKeyAllocator](
    [Key] [varchar](255) NOT NULL,
    [NextMax] [bigint] NOT NULL,
    CONSTRAINT [PK_LinearKeyAllocator] PRIMARY KEY CLUSTERED ([Key] ASC)
) ON [PRIMARY]

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