sql-server - T-SQL MERGE を高速化するために作成するインデックス

Question

テーブルに追加できるインデックス:

CREATE TABLE [WData](
    [Account] [varchar](50) NOT NULL,
    [Table] [varchar](50) NOT NULL,
    [BatchID] [datetime2](7) NOT NULL,
    [XmlRow] [xml] NULL
) ON [PRIMARY]

フォローアップストアドプロシージャがより速く実行されるようにするには? 現在、かなり遅いです。

create PROCEDURE [Update_WData]
    @Account VARCHAR(50),
    @Table VARCHAR(50),
    @BatchID DATETIME2,
    @XmlRows xml 
AS
BEGIN
    SET NOCOUNT ON;

    DECLARE @input TABLE (
        [XmlRow] xml NULL
    );
    INSERT INTO @input (XmlRow)
    SELECT 
        c1.query('.')
    FROM @XmlRows.nodes('/Block/NewRow') AS t(c1);

    DECLARE @output TABLE ([ACTION] NVARCHAR(50) );

    MERGE WData AS t
    USING @input AS s 
    ON (t.Account = @Account AND t.[Table]=@Table AND CONVERT(VARCHAR(max),t.XmlRow)=CONVERT(VARCHAR(max),s.XmlRow))

    WHEN NOT MATCHED BY TARGET 
        THEN INSERT (Account,[Table],BatchID, [XmlRow]) 
        VALUES (@Account, @Table, @BatchID, s.XmlRow )
    WHEN MATCHED AND t.BatchID <> @BatchID
        THEN UPDATE SET t.BatchID = @BatchID
    OUTPUT 
        $ACTION
    INTO @output;
    SELECT [Action], COUNT(*) AS [Count]
    FROM @Output
    GROUP BY [Action]
END