Windows Azure表存储行大小限制小于规定的1MB

Question

我已经使用这些来源对表存储及其大小限制,开销等进行了大量研究:

• http://blogs.msdn.com/b/windowsazurestorage/archive/2010/07/09/understanding-windows-azure-storage-billing-bandwidth-transactions-and-capacity.aspx
• http://msdn.microsoft.com/en-us/library/dd179338.aspx

使用这些信息,我写了一些代码来有效地存储多个属性的二进制数据,计算任何行和属性开销,并保持64KB属性限制和1MB行限制.

不幸的是它只是不起作用.作为一个例子,存储大约0.5MB返回400 Bad Request,说明实体太大 - 我不明白为什么它会被赋予1MB行大小限制.

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<error xmlns="http://schemas.microsoft.com/ado/2007/08/dataservices/metadata">
  <code>EntityTooLarge</code>
  <message xml:lang="en-GB">The entity is larger than allowed by the Table Service.</message>
</error>

我一直在使用的代码是相当简单的,但我可能在估算开销时犯了错误 - 但我怀疑它会被100%的数据大小所取消.

class Program
{
    static void Main(string[] args)
    {
        var client = CloudStorageAccount.DevelopmentStorageAccount.CreateCloudTableClient();
        var table = client.GetTableReference("sometable");
        table.CreateIfNotExists();

        const int rowOverhead = 4;
        const int maxRowSize = 1024 * 1024; // 1MB row size limit
        const int maxProperties = 252; // 255 less 3 system properties
        const int maxPropertySize = 64 * 1024; // 64KB property size limit

        var stream = new MemoryStream(new byte[512 * 1024]); // 0.5MB of data
        var entity = new DynamicTableEntity("pk", "rk");
        var buffer = new byte[maxPropertySize];
        var keySize = (entity.PartitionKey.Length + entity.RowKey.Length) * 2;
        var used = rowOverhead + keySize;

        for (var i = 0; i < maxProperties + 1; i++)
        {
            if (i > maxProperties)
            {
                throw new ArgumentException(string.Format("You have exceeded the column limit of {0}.", maxProperties));
            }

            var name = string.Concat("d", i);
            var overhead = CalculatePropertyOverhead(name, EdmType.Binary);
            var read = stream.Read(buffer, 0, maxPropertySize - overhead);
            used += read + overhead;

            if (used > maxRowSize)
            {
                throw new ArgumentException(string.Format("You have exceeded the max row size of {0} bytes.", maxRowSize));
            }

            if (read > 0)
            {
                var data = new byte[read];
                Array.Copy(buffer, 0, data, 0, read);
                entity.Properties.Add(name, new EntityProperty(data));
            }
            else
            {
                break;
            }
        }

        Console.WriteLine("Total entity size: {0}", used);
        table.Execute(TableOperation.InsertOrReplace(entity));
    }

    static int CalculatePropertyOverhead(string name, EdmType type)
    {
        const int propertyOverhead = 8;
        int propertyNameSize = name.Length * 2;
        int propertyTypeSize;

        switch (type)
        {
            case EdmType.Binary:
            case EdmType.Int32:
            case EdmType.String:
                propertyTypeSize = 4;
                break;
            case EdmType.Boolean:
                propertyTypeSize = 1;
                break;
            case EdmType.DateTime:
            case EdmType.Double:
            case EdmType.Int64:
                propertyTypeSize = 8;
                break;
            case EdmType.Guid:
                propertyTypeSize = 16;
                break;
            default:
                throw new NotSupportedException();
        }

        return propertyOverhead + propertyNameSize + propertyTypeSize;
    }
}

任何帮助解释我缺少的东西是值得赞赏的!

谢谢,

马蒂亚斯

Answer 1

Mattias，您所指的限制是针对实际存储服务的，但您的目标是本地存储模拟器。模拟器使用本地 SQL Server 作为其后备存储，并且具有与实际存储服务不同的限制。有关详细信息，请参阅http://msdn.microsoft.com/en-us/library/windowsazure/gg433135.aspx，特别是这一行：

* The total size of a row in a table in the storage emulator is limited to less than 1 MB.