EntityFramework 在执行更新查询时非常缓慢

Question

我们正在调查 EF 6.1.3 运行缓慢的性能问题，我们无法弄清楚可能是什么原因造成的。

数据库上下文初始化为：

Configuration.ProxyCreationEnabled = false;
Configuration.AutoDetectChangesEnabled = false;
Configuration.ValidateOnSaveEnabled = false;

我们已将性能问题隔离为以下方法：

protected virtual async Task<long> UpdateEntityInStoreAsync(T entity,
                                                            string[] changedProperties)
{
    using (var session = sessionFactory.CreateReadWriteSession(false, false))
    {
        var writer = session.Writer<T>();
        writer.Attach(entity);
        await writer.UpdatePropertyAsync(entity, changedProperties.ToArray()).ConfigureAwait(false);
    }
    return entity.Id;
}

changedProperties 列表中有两个名称，EF 正确生成了一个更新语句，只更新这两个属性。

This method is called repeatedly (to process a collection of data items) and takes about 15-20 seconds to complete.

If we replace the method above with the following, execution time drops to 3-4 seconds:

protected virtual async Task<long> UpdateEntityInStoreAsync(T entity,
                                                            string[] changedProperties)
{
    var sql = $"update {entity.TypeName()}s set";
    var separator = false;
    foreach (var property in changedProperties)
    {
         sql += (separator ? ", " : " ") + property + " = @" + property;
         separator = true;
    }
    sql += " where id = @Id";
    var parameters = (from parameter in changedProperties.Concat(new[] { "Id" })
                      let property = entity.GetProperty(parameter)
                      select ContextManager.CreateSqlParameter(parameter, property.GetValue(entity))).ToArray();
    using (var session = sessionFactory.CreateReadWriteSession(false, false))
    {
        await session.UnderlyingDatabase.ExecuteSqlCommandAsync(sql, parameters).ConfigureAwait(false);
    }
    return entity.Id;
}

The UpdatePropertiesAsync method called on the writer (a repository implementation) looks like this:

public virtual async Task UpdatePropertyAsync(T entity, string[] changedPropertyNames, bool save = true)
{
    if (changedPropertyNames == null || changedPropertyNames.Length == 0)
    {
        return;
    }

    Array.ForEach(changedPropertyNames, name => context.Entry(entity).Property(name).IsModified = true);
    if (save)
        await context.SaveChangesAsync().ConfigureAwait(false);
    }
}

What is EF doing that completely kills performance? And is there anything we can do to work around it (short of using another ORM)?

Answer 1

通过对代码计时，我能够看到 EF 花费的额外时间是在将对象附加到上下文的调用中，而不是在更新数据库的实际查询中。

通过消除所有对象引用（null在附加对象之前将它们设置为并在更新完成后恢复它们），EF 代码在“可比较的时间”（5 秒，但有大量日志记录代码）中运行到手写解决方案。

所以看起来EF有一个“错误”（有些人可能称之为功能）导致它递归检查附加的对象，即使更改跟踪和验证已被禁用。

更新：EF 7 似乎通过允许您在调用 Attach 时传入 GraphBehavior 枚举来解决此问题。