3，使用OpenQuery查询，OpenQuery将查询语句直接在Linked Server上执行，返回查询的结果。
OpenQuery Executes the specified pass-through query on the specified linked server. select sum(t.cnt) as cnt from ( select count(0) as cnt from dbo.commits c with(nolock) where day(c.[CreatedDate])=1 UNION all select p.cnt from openquery(db2, N'select count(0) as cnt from dbo.commits c with(nolock) where day(c.[CreatedDate])=1') as p UNION all select p.cnt from openquery(db3, N'select count(0) as cnt from dbo.commits c with(nolock) where day(c.[CreatedDate])=1') as p ) as t cost:105s，还是很高. |
4，使用C# 多线程编程，创建三个Task同时运行在三台Server上，Cost：28s
static void Main(string[] args) { List<Task> tasks = new List<Task>(); int c1=0, c2=0, c3=0; Task t1 = new Task(()=> { c1= GetCount("xxx"); }); Task t2 = new Task(() => { c2= GetCount("xxx"); }); Task t3 = new Task(() => { c3= GetCount("xxx"); }); tasks.Add(t1); tasks.Add(t2); tasks.Add(t3); Stopwatch sw = new Stopwatch(); sw.Start(); t1.Start(); t2.Start(); t3.Start(); Task.WaitAll(tasks.ToArray()); int sum = c1 + c2 + c3; sw.Stop(); Console.Read(); } static int GetCount(string str) { using (SqlConnection con = new SqlConnection(str)) { con.Open(); var cmd = con.CreateCommand(); cmd.CommandText = @" select count(0) as cnt from dbo.commits c with(nolock) where day(c.[CreatedDate]) = 1"; int count = (int)cmd.ExecuteScalar(); con.Close(); return count; } } |
5，结论
· 将数据水平切分，分布式部署在不同的SQL Server上，其查询性能并不一定比单一DB性能更好。
· 使用OpenQuery函数将查询语句在Remote Server上执行，返回查询结果，能够优化Linked Server 的查询性能。
· 在使用分布式数据库查询数据时，针对特定的应用，编写特定的代码，这需要fore-end 更多的参与。
