SQL Update Query with from clause Optimization - sql-server

Question

I have two tables which are heavily queried by multiple users. Average 100+ (update/select) queries/second requests are made for these tables.
Parent
Child
*GrantParent is not involved in join so, I said only two tables
I need to reorder all children for each parent. There can be 3000-4000 parents and each parent may have around same number of children.
Column Types:
ParentID GUID
ChildIndex int
FileID Varchar
IsDeleted bit
Tables have clustered index on PK and non-clustered index on columns being used in where.
UPDATE C SET C.ChildIndex = T.ReOrderedChildIndex FROM [Child] C INNER JOIN
(
SELECT ROW_NUMBER() OVER (PARTITION BY dbo.Child.[ParentID] ORDER BY [ChildIndex] asc) AS ReOrderedChildIndex,
dbo.Child.ChildIndex,
dbo.Child.FileID,
dbo.Child.ParentID
FROM dbo.Child WITH (NOLOCK) INNER JOIN
dbo.Parent WITH (NOLOCK) ON dbo.Child.ParentID = dbo.Parent.ParentID
WHERE (dbo.Parent.GrandParentID = 1) AND (dbo.Child.IsDeleted = 0)
) T
ON C.FileID =T.FileID AND (C.ParentID=T.ParentID) AND (C.IsDeleted = 0)
It looks above query take longer time and put select queries on wait even I have used WITH (NOLOCK) in all data selection stored procedures.
There is another query which reorder parents in same way as done for childs in above query.
In Activity Monitor the locks are shown for select stored procedures.
What is the best way to reorder perform reordering?
I am having following issues and believe they are stems from these queries:
1- Randomly deadlock occur.
2- Often connection pool time out occurs.
*Database is accessed by a windows application using Entlib 4.0 with connection pooling enabled, pool max size 200.
SQL Server 2008 R2

Answer 1

I'd recommend restructuring your data to a more flexible schema. This schema will allow multiple levels so you can merge GrandParent, Parent, and Child into one logical relationship table and one logical details table. You'll also be able to take advantage of indexes to reduce locks and improve performance.
You'll have to re-build your hierarchy after any relationship changes. The way I wrote the script below should minimize this impact on your system. You will no longer be updating the entire table, just the pieces that have changed.
Schema:
CREATE TABLE dbo.EntityName
(
ID INT IDENTITY(1,1),
ParentID INT -- Todo: Add foreign key back to dbo.EntityName
-- Todo: Add primary key
);
GO
CREATE TABLE dbo.Hierarchy
(
ParentID INT, -- Todo: Add foreign key back to dbo.EntityName
ChildID INT, -- Todo: Add foreign key back to dbo.EntityName
ChildLevel INT
);
GO
Populate script (slightly rough around the edges):
CREATE PROCEDURE [dbo].[uspBuildHierarchy]
AS
BEGIN
SET NOCOUNT ON;
CREATE TABLE #Hierarchy
(
ParentID INT,
ChildID INT,
ChildLevel INT
);
-- Add the root of your hierarchy
INSERT INTO #Hierarchy VALUES (1, 1, 0);
DECLARE #ChildLevel INT = 1,
#LastCount INT = 1;
WHILE (#LastCount > 0)
BEGIN
INSERT INTO #Hierarchy
SELECT
E.ParentID,
E.ID,
#ChildLevel + 1
FROM dbo.EntityName E
INNER JOIN #Hierarchy H ON H.ChildID = E.ParentID
AND H.ChildLevel = (#ChildLevel - 1)
LEFT JOIN #Hierarchy EH ON EH.ParentID = E.ParentID
AND EH.ChildID = E.ID
WHERE EH.ChildLevel IS NULL;
SET #LastCount = ##ROWCOUNT;
SET #ChildLevel = #ChildLevel + 1;
END
MERGE INTO dbo.Hierarchy OH
USING
(
SELECT
ParentID,
ChildID,
ChildLevel
FROM #Hierarchy
) NH
ON OH.ParentID = NH.ParentID
AND OH.ChildID = NH.ChildID
WHEN MATCHED AND OH.ChildLevel <> NH.ChildLevel THEN
UPDATE
SET ChildLevel = NH.ChildLevel
WHEN NOT MATCHED THEN
INSERT
VALUES
(
NH.ParentID,
NH.ChildID,
NH.ChildLevel
)
WHEN NOT MATCHED BY SOURCE
THEN DELETE;
END
GO
Query for all of an entity's children:
SELECT *
FROM dbo.EntityName E
INNER JOIN dbo.Hierarchy H ON H.ChildID = E.ID
AND H.ParentID = #EntityNameID;