.NET分布式Orleans - 6 - 事件溯源
基本概念事件溯源(Event Sourcing)是一种设计模式,它记录并存储了应用程序状态变化的所有事件。
其核心思想是将系统中的每次状态变化都视为一个事件,并将这些事件以时间顺序的方式持久化存储。
这样,通过重放这些事件,我们可以重建系统在任何特定时间点的状态。
每个事件通常都包含了描述状态变化的必要信息,以及发生状态变化的原因和时间戳。
工作原理
工作原理方面,事件溯源主要依赖于两个关键部分:事件生成和事件存储。
当系统中发生状态变化时,会生成一个或多个事件,这些事件随后被存储到事件存储中。
事件存储需要设计成高可用、高一致且可伸缩的,以支持大规模的系统操作。
之后,当需要重建系统状态时,只需从事件存储中按顺序读取事件,并依次应用这些事件到系统状态即可。
使用场景
在Orleans7中,事件溯源主要应用在以下几个场景:
[*]分布式系统状态同步:在分布式系统中,各个节点之间的状态同步是一个重要问题。通过事件溯源,每个节点都可以记录并发送自己的状态变化事件,其他节点则可以通过订阅这些事件来同步自己的状态。
[*]历史数据追踪和审计:在某些业务场景下,需要追踪系统的历史操作记录,以进行审计或分析。事件溯源提供了完整的操作历史,可以方便地查询和回放历史事件。
[*]容错和恢复:当系统发生故障时,通过事件溯源可以方便地恢复到故障发生前的状态,或者根据事件日志进行故障排查。
优势
事件溯源在Orleans7中带来了以下优势:
[*]数据完整性和一致性:由于事件溯源记录了所有状态变化的历史,因此可以确保数据的完整性和一致性。
[*]灵活性和可扩展性:事件溯源的设计使得系统可以很容易地添加新的状态变化事件,同时也支持大规模的系统扩展。
[*]容错和恢复能力:通过事件溯源,可以轻松地恢复到系统的任何历史状态,大大提高了系统的容错和恢复能力。
[*]清晰的业务逻辑:每个事件都代表了一个具体的业务操作,因此通过查看事件日志,可以清晰地了解系统的业务逻辑和操作流程。
总的来说,事件溯源是一种强大而灵活的设计模式,它在Orleans7中的应用为分布式系统带来了诸多优势。对于软件开发者来说,理解和掌握事件溯源机制,将有助于构建更加健壮、可靠和可扩展的分布式系统。
示例
下面使用事件溯源,来跟踪一个账户的变更记录。
首先需要安装必须的nuget包
然后设置Orleans,除了Orleans的常规设置外,还需要 siloHostBuilder.AddLogStorageBasedLogConsistencyProvider("LogStorage") 来设置LogConsistencyProvider
builder.Host.UseOrleans(static siloHostBuilder =>
{
var invariant = "System.Data.SqlClient";
var connectionString = "Data Source=localhost\\SQLEXPRESS;Initial Catalog=orleanstest;User Id=sa;Password=12334;";
siloHostBuilder.AddLogStorageBasedLogConsistencyProvider("LogStorage");
// Use ADO.NET for clustering
siloHostBuilder.UseAdoNetClustering(options =>
{
options.Invariant = invariant;
options.ConnectionString = connectionString;
}).ConfigureLogging(logging => logging.AddConsole());
siloHostBuilder.Configure<ClusterOptions>(options =>
{
options.ClusterId = "my-first-cluster";
options.ServiceId = "SampleApp";
});
// Use ADO.NET for persistence
siloHostBuilder.AddAdoNetGrainStorage("GrainStorageForTest", options =>
{
options.Invariant = invariant;
options.ConnectionString = connectionString;
//options.GrainStorageSerializer = new JsonGrainStorageSerializer()
});
});定义账户的存储和提取事件类
// the classes below represent events/transactions on the account
// all fields are user-defined (none have a special meaning),
// so these can be any type of object you like, as long as they are serializable
// (so they can be sent over the wire and persisted in a log).
public abstract class Transaction
{
/// <summary> A unique identifier for this transaction</summary>
public Guid Guid { get; set; }
/// <summary> A description for this transaction</summary>
public string Description { get; set; }
/// <summary> time on which the request entered the system</summary>
public DateTime IssueTime { get; set; }
}
public class DepositTransaction : Transaction
{
public uint DepositAmount { get; set; }
}
public class WithdrawalTransaction : Transaction
{
public uint WithdrawalAmount { get; set; }
}再定义账户的Grain,其中有存钱,取钱,获取余额,与变更记录操作
Grain类必须具有 LogConsistencyProviderAttribute 才能指定日志一致性提供程序。 还需要 StorageProviderAttribute设置存储。
/// <summary>
/// An example of a journaled grain that models a bank account.
///
/// Configured to use the default storage provider.
/// Configured to use the LogStorage consistency provider.
///
/// This provider persists all events, and allows us to retrieve them all.
/// </summary>
/// <summary>
/// A grain that models a bank account
/// </summary>
public interface IAccountGrain : IGrainWithStringKey
{
Task<uint> Balance();
Task Deposit(uint amount, Guid guid, string desc);
Task<bool> Withdraw(uint amount, Guid guid, string desc);
Task<IReadOnlyList<Transaction>> GetTransactionLog();
}
public class AccountGrain : JournaledGrain<AccountGrain.GrainState, Transaction>, IAccountGrain
{
/// <summary>
/// The state of this grain is just the current balance.
/// </summary>
public class GrainState
{
public uint Balance { get; set; }
public void Apply(DepositTransaction d)
{
Balance = Balance + d.DepositAmount;
}
public void Apply(WithdrawalTransaction d)
{
if (d.WithdrawalAmount > Balance)
throw new InvalidOperationException("we make sure this never happens");
Balance = Balance - d.WithdrawalAmount;
}
}
public Task<uint> Balance()
{
return Task.FromResult(State.Balance);
}
public Task Deposit(uint amount, Guid guid, string description)
{
RaiseEvent(new DepositTransaction()
{
Guid = guid,
IssueTime = DateTime.UtcNow,
DepositAmount = amount,
Description = description
});
// we wait for storage ack
return ConfirmEvents();
}
public Task<bool> Withdraw(uint amount, Guid guid, string description)
{
// if the balance is too low, can't withdraw
// reject it immediately
if (State.Balance < amount)
return Task.FromResult(false);
// use a conditional event for withdrawal
// (conditional events commit only if the version hasn't already changed in the meantime)
// this is important so we can guarantee that we never overdraw
// even if racing with other clusters, of in transient duplicate grain situations
return RaiseConditionalEvent(new WithdrawalTransaction()
{
Guid = guid,
IssueTime = DateTime.UtcNow,
WithdrawalAmount = amount,
Description = description
});
}
public Task<IReadOnlyList<Transaction>> GetTransactionLog()
{
return RetrieveConfirmedEvents(0, Version);
}
}最后即可通过client生成grain,并获取账户变动记录
var palyer = client.GetGrain<IAccountGrain>("zhangsan");
await palyer.Deposit(1000, Guid.NewGuid(), "aaa");
var logs = await palyer.GetTransactionLog();
return Results.Ok(logs);
来源:https://www.cnblogs.com/chenyishi/p/18099103
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