Resiliency Policies

INFO

Marten's previous, homegrown IRetryPolicy mechanism was completely replaced by Polly in Marten V7.

Out of the box, Marten is using Polly for resiliency on most operations with this setup:

// default Marten policies
return builder
   .AddRetry(new()
    {
        ShouldHandle = new PredicateBuilder().Handle<NpgsqlException>().Handle<MartenCommandException>().Handle<EventLoaderException>(),
        MaxRetryAttempts = 3,
        Delay = TimeSpan.FromMilliseconds(50),
        BackoffType = DelayBackoffType.Exponential
    });

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The general idea is to have some level of retry with an exponential backoff on typical transient errors encountered in database usage (network hiccups, a database being too busy, etc.).

You can replace Marten's Polly configuration through:

using var store = DocumentStore.For(opts =>
{
    opts.Connection("some connection string");

    opts.ConfigurePolly(builder =>
    {
        builder.AddRetry(new()
        {
            ShouldHandle = new PredicateBuilder().Handle<NpgsqlException>().Handle<MartenCommandException>(),
            MaxRetryAttempts = 10, // this is excessive, but just wanted to show something different
            Delay = TimeSpan.FromMilliseconds(50),
            BackoffType = DelayBackoffType.Linear
        });
    });
});

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Or you can extend default marten configuration with your custom policies. Any user supplied policies will take precedence over the default policies.

using var store = DocumentStore.For(opts =>
{
    opts.Connection("some connection string");

    opts.ExtendPolly(builder =>
    {
        // custom policies are configured before marten default policies
        builder.AddRetry(new()
        {
            // retry on your custom exceptions (ApplicationException as an example)
            ShouldHandle = new PredicateBuilder().Handle<ApplicationException>(),
            MaxRetryAttempts = 3,
            Delay = TimeSpan.FromMilliseconds(50),
            BackoffType = DelayBackoffType.Linear
        });
    });
});

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