CLR 表值函数“流式传输"如何? [英] How is a CLR table valued function 'streaming''?

问题描述

有关表值 Sql Clr 函数的 MSDN 文档 状态:

Transact-SQL 表值函数实现调用的结果函数进入一个中间表....相比之下，CLR 表值函数表示流选择.没有要求整个结果集是在单个表中实现.这IEnumerable 对象返回托管函数被直接调用查询的执行计划调用表值函数，和结果被消耗在一个增量方式.......这也是一个更好的选择，如果你有返回大量行，因为他们不必是整体在内存中具体化.

Transact-SQL table-valued functions materialize the results of calling the function into an intermediate table. ... In contrast, CLR table-valued functions represent a streaming alternative. There is no requirement that the entire set of results be materialized in a single table. The IEnumerable object returned by the managed function is directly called by the execution plan of the query that calls the table-valued function, and the results are consumed in an incremental manner. ... It is also a better alternative if you have very large numbers of rows returned, because they do not have to be materialized in memory as a whole.

然后我发现没有数据访问是在填充行"方法中允许.这意味着您仍然必须在 init 方法中执行所有数据访问并将其保存在内存中，等待调用填充行".我是不是误解了什么?如果我不强制将结果放入数组或列表中，则会收到错误消息:'ExecuteReader 需要一个打开且可用的连接.连接的当前状态是关闭的.'

Then I find out that no data access is allowed in the 'Fill row' method. This means that you still have to do all of your data access in the init method and keep it in memory, waiting for 'Fill row' to be called. Have I misunderstood something? If I don't force my results into an array or list, I get an error: 'ExecuteReader requires an open and available Connection. The connection's current state is closed.'

代码示例:

[<SqlFunction(DataAccess = DataAccessKind.Read, FillRowMethodName = "Example8Row")>]
static member InitExample8() : System.Collections.IEnumerable = 
   let c = cn() // opens a context connection
   // I'd like to avoid forcing enumeration here:
   let data = getData c |> Array.ofSeq
   data :> System.Collections.IEnumerable

static member Example8Row ((obj : Object),(ssn: SqlChars byref)) = 
   do ssn <- new SqlChars(new SqlString(obj :?> string))
   ()

我在这里处理数百万行.有没有办法懒惰地做到这一点?

I'm dealing with several million rows here. Is there any way to do this lazily?

推荐答案

我假设您使用的是 SQL Server 2008.正如一位 Microsoft 员工在 本页, 2008 需要方法标记使用 DataAccessKind.Read 比 2005 年更频繁.其中一次是当 TVF 参与事务时(我测试时似乎总是如此).解决方法是在连接字符串中指定enlist=false，可惜不能和context connection=true结合使用.这意味着您的连接字符串需要采用典型的客户端格式:Data Source=.;Initial Catalog=MyDb;Integrated Security=sspi;Enlist=false 并且您的程序集必须使用 permission_set= 创建external_access，至少.以下工作:

I'm assuming you're using SQL Server 2008. As mentioned by a Microsoft employee on this page, 2008 requires methods to be marked with DataAccessKind.Read much more frequently than 2005. One of those times is when the TVF participates in a transaction (which seemed to always be the case, when I tested). The solution is to specify enlist=false in the connection string, which, alas, cannot be combined with context connection=true. That means your connection string needs to be in typical client format: Data Source=.;Initial Catalog=MyDb;Integrated Security=sspi;Enlist=false and your assembly must be created with permission_set=external_access, at minimum. The following works:

using System;
using System.Collections;
using System.Data.SqlClient;
using System.Data.SqlTypes;
using Microsoft.SqlServer.Server;

namespace SqlClrTest {
    public static class Test {
        [SqlFunction(
            DataAccess = DataAccessKind.Read,
            SystemDataAccess = SystemDataAccessKind.Read,
            TableDefinition = "RowNumber int",
            FillRowMethodName = "FillRow"
            )]
        public static IEnumerable MyTest(SqlInt32 databaseID) {
            using (var con = new SqlConnection("data source=.;initial catalog=TEST;integrated security=sspi;enlist=false")) {
                con.Open();
                using (var cmd = new SqlCommand("select top (100) RowNumber from SSP1 where DatabaseID = @DatabaseID", con)) {
                    cmd.Parameters.AddWithValue("@DatabaseID", databaseID.IsNull ? (object)DBNull.Value : databaseID.Value);
                    using (var reader = cmd.ExecuteReader()) {
                        while (reader.Read())
                            yield return reader.GetInt32(0);
                    }
                }
            }
        }
        public static void FillRow(object obj, out SqlInt32 rowNumber) {
            rowNumber = (int)obj;
        }
    }
}

在 F# 中也有同样的事情:

Here's the same thing in F#:

namespace SqlClrTest

module Test =

    open System
    open System.Data
    open System.Data.SqlClient
    open System.Data.SqlTypes
    open Microsoft.SqlServer.Server

    [<SqlFunction(
        DataAccess = DataAccessKind.Read,
        SystemDataAccess = SystemDataAccessKind.Read,
        TableDefinition = "RowNumber int",
        FillRowMethodName = "FillRow"
        )>]
    let MyTest (databaseID:SqlInt32) =
        seq {
            use con = new SqlConnection("data source=.;initial catalog=TEST;integrated security=sspi;enlist=false")
            con.Open()
            use cmd = new SqlCommand("select top (100) RowNumber from SSP1 where DatabaseID = @DatabaseID", con)
            cmd.Parameters.AddWithValue("@DatabaseID", if databaseID.IsNull then box DBNull.Value else box databaseID.Value) |> ignore
            use reader = cmd.ExecuteReader()
            while reader.Read() do
                yield reader.GetInt32(0)
        } :> System.Collections.IEnumerable

    let FillRow (obj:obj) (rowNumber:SqlInt32 byref) =
        rowNumber <- SqlInt32(unbox obj)

好消息是:微软认为这是一个错误.

这篇关于CLR 表值函数“流式传输"如何?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！