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POChange in query plan and execution time with TOP and ESCAPE
 

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  1. POChange in query plan and execution time with TOP and ESCAPE
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    <p>One of the query (given below) is taking 90+ seconds to execute. It returns ~500 rows from a rather large table LogMessage. If <code>ESCAPE N'~'</code> is removed from the query it executes within few seconds. Similarly if <code>TOP (1000)</code> is removed, it executes within few seconds. The query plan shows <code>Key Lookup (Clustered) PK_LogMessage, Index Scan (NonClustered) IX_LogMessage and Nested Loops (Inner Join)</code> in the first case. When the clauses <code>ESCAPE N'~'</code> or <code>TOP (1000)</code> are removed the query plan changes and shows <code>Clustered Index Scan (Clustered) PK_LogMessage</code>. While we are looking into adding more indexes (probably on ApplicationName), we would like to understand what is going on currently.</p> <p>The query is being generated from <code>Entity Framework</code> in case you wonder why it is being written this way. Also the actual query is more complex but this is the shortest possible version that exhibits the same behavior.</p> <p>Query:</p> <pre><code>SELECT TOP (1000) [Project1].[MessageID] AS [MessageID], [Project1].[TimeGenerated] AS [TimeGenerated], [Project1].[SystemName] AS [SystemName], [Project1].[ApplicationName] AS [ApplicationName] FROM ( SELECT [Project1].[MessageID] AS [MessageID], [Project1].[TimeGenerated] AS [TimeGenerated], [Project1].[SystemName] AS [SystemName], [Project1].[ApplicationName] AS [ApplicationName] FROM ( SELECT [Extent1].[MessageID] AS [MessageID], [Extent1].[TimeGenerated] AS [TimeGenerated], [Extent1].[SystemName] AS [SystemName], [Extent1].[ApplicationName] AS [ApplicationName] FROM [dbo].[LogMessage] AS [Extent1] INNER JOIN [dbo].[LogMessageCategory] AS [Extent2] ON [Extent1].[CategoryID] = [Extent2].[CategoryID] WHERE ([Extent1].[ApplicationName] LIKE N'%tier%' ESCAPE N'~') ) AS [Project1] ) AS [Project1] ORDER BY [Project1].[TimeGenerated] DESC </code></pre> <p>Table LogMessage:</p> <pre><code>CREATE TABLE [dbo].[LogMessage]( [MessageID] [int] IDENTITY(1000001,1) NOT NULL, [TimeGenerated] [datetime] NOT NULL, [SystemName] [nvarchar](256) NOT NULL, [ApplicationName] [nvarchar](512) NOT NULL, [CategoryID] [int] NOT NULL, CONSTRAINT [PK_LogMessage] PRIMARY KEY CLUSTERED ( [MessageID] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, FILLFACTOR = 90) ON [PRIMARY] ) ON [PRIMARY] ALTER TABLE [dbo].[LogMessage] WITH CHECK ADD CONSTRAINT [FK_LogMessage_LogMessageCategory] FOREIGN KEY([CategoryID]) REFERENCES [dbo].[LogMessageCategory] ([CategoryID]) ALTER TABLE [dbo].[LogMessage] CHECK CONSTRAINT [FK_LogMessage_LogMessageCategory] ALTER TABLE [dbo].[LogMessage] ADD DEFAULT ((100)) FOR [CategoryID] CREATE NONCLUSTERED INDEX [IX_LogMessage] ON [dbo].[LogMessage] ( [TimeGenerated] DESC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, FILLFACTOR = 90) ON [PRIMARY] </code></pre> <p>Table LogMessageCategory:</p> <pre><code>CREATE TABLE [dbo].[LogMessageCategory]( [CategoryID] [int] NOT NULL, [Name] [nvarchar](128) NOT NULL, [Description] [nvarchar](256) NULL, CONSTRAINT [PK_LogMessageCategory] PRIMARY KEY CLUSTERED ( [CategoryID] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] ) ON [PRIMARY] </code></pre> <p>Query Plan 1 (takes 90+ seconds)</p> <p><img src="https://i.stack.imgur.com/UVyX2.png" alt="Query Plan 1 (takes 90+ seconds)"></p> <p>Query Plan 2 (takes ~3 seconds)</p> <p><img src="https://i.stack.imgur.com/hIy6O.png" alt="Query Plan 2 (takes ~3 seconds)"></p>
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    1. USMartin Smith
    1. USamit_g
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      1. POChange in query plan and execution time with TOP and ESCAPE
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      1. VTUpMod
    2. VO
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    1. COCan you post the exact code for execution plan 1 and 2? The plan does not seem to match the query posted. The query has a join to the LogMessageCategory table but that is not represented in the execution plan (should be an INNER JOIN). Also the LogMessage table does not have a CategoryID.
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      1. US8kb
    2. COI'm also confused by the ESCAPE usage. Typically ESCAPE is used to make a wildcard part of the search. For example, you would use LIKE '%50~%%' ESCAPE '~' to search for all strings that contain "50%". But your LIKE statement does not contain a '~'
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      1. POChange in query plan and execution time with TOP and ESCAPE
      1. US8kb
    3. CO@8kb, this is the query plan displayed in SQLMS.
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      1. USamit_g
 

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