SQL 链接服务器查询非常非常慢

2021-09-10 00:00:00 sql tsql sql-server

我正在通过链接服务器从 VIEWS 中提取大量数据.我使用的是 SQL Server 2012，链接服务器是 SQL Server 2008

I am extracting large amount of data via linked server from VIEWS. I am using SQL Server 2012 and linked server is SQL Server 2008

我的选择语句是

SELECT * INTO MY_LOCAL_TABLE
FROM 
(    SELECT * FROM LINKEDSERVER.DB.TABLE.VIEW
     WHERE DATE>'2012-01-01' AND ID IN (SELECT ID FROM MY_LOCAL_VIEW) 
) Q

我期待 300K 行有将近 700 个 ID.以前需要几个小时，但现在需要 20 多个小时！！

I am expecting 300K rows for nearly 700+ IDs. before it used to take couple of hours but now its take more than a 20 hr!!

您能否为此 PAIN 提出任何替代解决方案?

Could you please suggest any alternative solution for this PAIN??

非常感谢！

推荐答案

当您使用由 4 部分组成的名称时，例如 [server].db.dbo.table，尤其是在 中join，很多时候整个表都通过网络复制到本地机器上，这显然不太理想.

When you use a 4-part name such as [server].db.dbo.table, especially in a join, often times the entire table is copied over the wire to the local machine, which is obviously not ideal.

更好的方法是使用 OPENQUERY -- 在源(链接服务器)处理.

A better approach is to use an OPENQUERY -- which is handled at the source (linked server).

试试:

SELECT *
FROM OPENQUERY([LINKEDSERVER], 'SELECT * FROM DB.TABLE.VIEW WHERE DATE>'2012-01-01')
AND ID IN (SELECT ID FROM MY_LOCAL_VIEW)

使用这种方法，链接服务器将返回日期 > x 的所有行，然后本地服务器将通过本地表中的 ID 过滤该行.

With this approach the linked server will return all rows for date > x, and then the local server will filter that by ID's in your local table.

当然，索引仍然会影响 SELECT * FROM DB.TABLE.VIEW WHERE DATE>'2012-01-01.

Of course, indexing will still play a factor for doing SELECT * FROM DB.TABLE.VIEW WHERE DATE>'2012-01-01.

我在大型子集上使用的另一种方法是将本地 ID 转储到远程服务器，然后远程处理它，例如:

Another approach, which I use on large subsets, is to dump the local ID's to the remote server, THEN handle it all remotely, such as:

    -- copy local table to linked server by executing remote query 
    DECLARE @SQL NVARCHAR(MAX)
    SET @SQL = 'SELECT ID INTO db.dbo.tmpTable FROM [SERVER].DB.DBO.MY_LOCAL_VIEW'
    EXEC(@SQL) AT [LINKEDSERVER]

   -- index remote table?!?
    DECLARE @SQL NVARCHAR(MAX)
    SET @SQL = 'CREATE INDEX [IXTMP] ON db.dbo.tmpTable (ID)'
    EXEC(@SQL) AT [LINKEDSERVER]

    -- run query on local machine against both remote tables
    SELECT *
    -- INTO sometable
    FROM OPENQUERY([LINKEDSERVER], 'SELECT * 
                                    FROM DB.TABLE.VIEW
                                    WHERE DATE>''2012-01-01''
                                    AND ID IN (SELECT ID FROM db.dbo.tmpTable)')

    -- now drop remote temp table of id's
    DECLARE @SQL NVARCHAR(MAX)
    SET @SQL = 'DROP TABLE db.dbo.tmpTable'
    EXEC(@SQL) AT [LINKEDSERVER]

如果本地视图也很大，那么您可以考虑执行一个使用 openquery 返回本地机器的远程查询(假设远程机器有本地作为链接).

If the local view is also large, then you may consider executing a remote query that uses an openquery back to the local machine (assuming the remote machine has the local as a link).

-- copy local table to linked server by executing remote query 
DECLARE @SQL NVARCHAR(MAX)
SET @SQL = 'SELECT ID INTO db.dbo.tmpTable FROM OPENQUERY([SERVER], ''SELECT ID FROM DB.DBO.MY_LOCAL_VIEW'')'
EXEC(@SQL) AT [LINKEDSERVER]

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