我使用以下资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，我编写了一些代码来有效地跨多个属性存储二进制数据，计算任何行和属性开销并保持在 64KB 属性限制和 1MB 行限制内。
不幸的是，它只是行不通。例如，存储大约 0.5MB 会返回 400 Bad Request 说明实体太大 - 我不明白为什么会给出 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相当简单，但我可能在估计开销时犯了错误——但我怀疑它会偏离数据大小的 100%。
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;
}
}
感谢您解释我所缺少的任何帮助！
谢谢，
马蒂亚斯