链接服务器插入选择性能 [英] Linked Server Insert-Select Performance

问题描述

假设我的本地表为Local_Table，并且我有另一台服务器，另一个数据库和表为Remote_Table(表结构相同).

Assume that I have a table on my local which is Local_Table and I have another server and another db and table, which is Remote_Table (table structures are the same).

Local_Table有数据，Remote_Table没有.我想通过以下查询将数据从Local_Table传输到Remote_Table:

Local_Table has data, Remote_Table doesn't. I want to transfer data from Local_Table to Remote_Table with this query:

Insert into RemoteServer.RemoteDb..Remote_Table
select * from Local_Table (nolock)

但是性能却很慢.

但是，当我使用SQL Server导入和导出向导时，传输确实非常快.

However, when I use SQL Server import-export wizard, transfer is really fast.

我做错了什么?为什么使用Import-Export向导很快，而使用insert-select语句却慢呢?有什么想法吗?

What am I doing wrong? Why is it fast with Import-Export wizard and slow with insert-select statement? Any ideas?

推荐答案

最快的方法是提取数据而不是推送数据.推入表后，每一行都需要一个连接，一个插入和一个断开连接.

The fastest way is to pull the data rather than push it. When the tables are pushed, every row requires a connection, an insert, and a disconnect.

如果由于服务器之间具有单向信任关系而无法提取数据，则解决方法是将整个表构造为巨型T-SQL语句，然后立即运行所有表.

If you can't pull the data, because you have a one way trust relationship between the servers, the work around is to construct the entire table as a giant T-SQL statement and run it all at once.

DECLARE @xml XML

SET @xml = (
        SELECT 'insert Remote_Table values (' + '''' + isnull(first_col, 'NULL') + ''',' +
            -- repeat for each col
            '''' + isnull(last_col, 'NULL') + '''' + ');'
        FROM Local_Table
        FOR XML path('')
        ) --This concatenates all the rows into a single xml object, the empty path keeps it from having <colname> </colname> wrapped arround each value

DECLARE @sql AS VARCHAR(max)

SET @sql = 'set nocount on;' + cast(@xml AS VARCHAR(max)) + 'set nocount off;' --Converts XML back to a long string

EXEC ('use RemoteDb;' + @sql) AT RemoteServer

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