问题描述
我有一个 SQL 查询喜欢
I have a SQL query Like
SELECT Column1, Column2, Column3, **ufn_HugeTimeProcessFunction**(Column1, Column2, @Param1) As Column4
From Table1
这个 ufn_HugeTimeProcessFunction 函数针对大表(就行数而言)运行，并且后面有几个计算返回值.
This ufn_HugeTimeProcessFunction function run against large table (in terms of number of rows) and there are several calculation behind to return value.
我能否强制 SQL 编译器在另一个线程(进程)中运行该函数?
Am I able to force the SQL compiler to run that function in another thread (process)?
已基本上该函数从 3 个不同的数据库中获取数据.这就是为什么我打算并行"运行它，而且不可能更改其他数据库上的索引
Edited : Basically that function get the data from 3 different databases. That's why I am planing to run it "in parallel", moreover it is not possible to change the indexes on the other databases
推荐答案
简而言之，SQL server 本身就可以很好地判断一个查询是否可以在多个线程中运行.基本上查询优化器会查看查询的各个部分是否可以并行运行并接受调用.
In brief, SQL server itself is a good judge of whether a query can be run in multiple threads or not. Basically query optimizer sees if parts of the query can be run in parallel and takes a call.
如果查询包含无法并行运行的标量运算符或关系运算符，则不会考虑并行执行.此外，如果要操作的行数相对较少，查询优化器不会考虑并行执行计划.
照你的话来说，这个功能很耗时.所以外部选择和函数肯定会在不同的线程上运行.但是，如果没有 ufn_HugeTimeProcessFunction 的可见性，将很难提供优化并行运行函数的解决方案.如果没有，我建议您查看函数的执行计划，看看是否可以调整查询以减少标量和关系操作
Going by your words, the function is time consuming. So external select and the function will most definitely be running on different threads. However, without visibility to the ufn_HugeTimeProcessFunction, it will be very difficult to provide a solution to optimize the function for parallel runs. In the absence of that, I would recommend you to have a look at the execution plan for the function and see if you can tweak the query to reduce scalar and relational operations
引用来源:http:///www.toadworld.com/platforms/sql-server/w/wiki/9824.parallel-query-processing.aspx
有关在分析执行计划后使用并行性的更多信息，请访问 https://www.simple-talk.com/sql/learn-sql-server/understanding-and-using-parallelism-in-sql-server/
More info on using parallelism after analyzing execution plans can be found at https://www.simple-talk.com/sql/learn-sql-server/understanding-and-using-parallelism-in-sql-server/
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