/// <summary>
/// 权重轮询调度算法
///
/// !CA763CA8DB2378D1!627.entry
/// </summary>
public class WeightedRoundRobinScheduling : ILoadBalanceScheduling
{
private static object lockHelper = new object();
/// <summary>
/// 快照的权重列表
/// </summary>
static List<int> snapWeightList = new List<int>();
/// <summary>
/// 当前的快照索引和权重信息
/// </summary>
static int curentSnapIndex, currentWeight;
/// <summary>
/// 快照权重列表中最大的权重值和最大公约数
/// </summary>
static int maxWeight, gcd;
static WeightedRoundRobinScheduling()
{
curentSnapIndex = -1;
currentWeight = 0;
snapWeightList = GetSnapWeightList();
maxWeight = GetMaxWeight(snapWeightList);
gcd = GCD(snapWeightList);
}
/// <summary>
/// 获取应用当前负载均衡调度算法下的快照链接信息
/// </summary>
/// <returns></returns>
public DbSnapInfo GetConnectDbSnap()
{
lock (lockHelper)
{
DbSnapInfo current = RoundRobinScheduling();
if (current != null)
return current;
else
return DbSnapConfigs.GetEnableSnapList()[0];
}
}
/// <summary>
/// 获取快照权重的列表
/// </summary>
/// <returns></returns>
static List<int> GetSnapWeightList()
{
List<int> snapWeightList = new List<int>();
foreach (DbSnapInfo dbSnapInfo in DbSnapConfigs.GetEnableSnapList())
{
snapWeightList.Add(dbSnapInfo.Weight);
}
return snapWeightList;
}
/// <summary>
/// 权重轮询调度算法
/// </summary>
static DbSnapInfo RoundRobinScheduling()
{
while (true)
{
curentSnapIndex = (curentSnapIndex + 1) % DbSnapConfigs.GetEnableSnapList().Count;
if (curentSnapIndex == 0)
{
currentWeight = currentWeight - gcd;
if (currentWeight <= 0)
{
currentWeight = maxWeight;
if (currentWeight == 0)
return null;
}
}
if (DbSnapConfigs.GetEnableSnapList()[curentSnapIndex].Weight >= currentWeight)
return DbSnapConfigs.GetEnableSnapList()[curentSnapIndex];
}
}
/// <summary>
/// 获取最大权重
/// </summary>
/// <param></param>
/// <returns></returns>
static int GetMaxWeight(List<int> snapWeightList)
{
int maxWeight = 0;
foreach (int snapWeight in snapWeightList)
{
if (maxWeight < snapWeight)
maxWeight = snapWeight;
}
return maxWeight;
}
/// <summary>
/// 获取权重的最大公约数
/// </summary>
/// <returns></returns>
static int GCD(List<int> snapWeightList)
{
// 排序，得到数字中最小的一个
snapWeightList.Sort(new WeightCompare());
int minNum = snapWeightList[0];
// 最大公约数肯定大于等于1，且小于等于最小的那个数。
// 依次整除，如果余数全部为0说明是一个约数，直到打出最大的那个约数
int gcd = 1;
for (int i = 1; i <= minNum; i++)
{
bool isFound = true;
foreach (int snapWeight in snapWeightList)
{
if (snapWeight % i != 0)
{
isFound = false;
break;
}
}
if (isFound)
gcd = i;
}
return gcd;
}
/// <summary>
/// 实现IComparer接口,用于对数字列表进行排序
/// </summary>
private class WeightCompare : System.Collections.Generic.IComparer<int>
{
public int Compare(int weightA, int weightB)
{
return weightA - weightB;
}
}
}
到这里，主要的功能代码就介绍的差不多了，我们可以通过对dbsnap.config的相应节点配置，来灵活定制我们的负载均衡方案。同时，对一般开发者而言，这种架构是透明的，大家可以完全在不了解它的情况下开发自己的数据访问功能，并通过相应开关来让自己的代码支持均衡负载。
当然这个方案还有一些没考虑到的问题比如：
1.对‘主从数据库的健康度检查'，即如果主或从数据库出现故障的时候该如何处理，当然在sqlserver中还提供了镜像功能来解决类似问题，所以它也可做为一个备选方案。
2.当主数据库被发布出去后，主数据库的表和存储过程就会被‘锁定'，其不允许被再次修改了，所以还要继续研究如何解决这一问题。
原文链接:
作者: daizhj, 代震军
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