The strategy selected by the query optimiser to process a query.

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Better execution plan if parameter is stored in local variable

I have two stored procedures. This one is incredibly fast (~ 2 seconds) CREATE PROCEDURE [schema].[Test_fast] @week date AS BEGIN declare @myweek date = @week select distinct serial ...
7
votes
1answer
329 views

Why SELECT COUNT() query execution plan includes left joined table?

In SQL Server 2012 I have table valued function with join to another table I need to to count number of rows for this 'table valued function'. When I inspect the execution plan, I can see the left ...
7
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1answer
722 views

How does SQL Server's optimizer estimate the number of rows in a joined table?

I am running this query in the AdventureWorks2012 database: SELECT s.SalesOrderID, d.CarrierTrackingNumber, d.ProductID, d.OrderQty FROM Sales.SalesOrderHeader s JOIN ...
7
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1answer
144 views

Two columns with and without index in where clause - How index works

I am executing a query on SQL Server 2008: SELECT col1 FROM table1 WHERE col2=val2 AND col3=val3 Here col2 has a non-clustered index, col1 is the PRIMARY KEY, and col3 does not have any index. ...
7
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1answer
1k views

Query is slow in SQL Server 2014, fast in SQL Server 2012

During the migration of one of our databases from SQL Server 2012 (SP1, CU2) to SQL Server 2014 (SP1), we have experienced some strange issues. One of the queries that completes within seconds on SQL ...
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1answer
2k views

How does SQL Server generate a query execution plan that adds up to 6,000%? [duplicate]

Today I was on The Heap and was looking at a query plan for something I thought could be improved. However, it created something that shook my belief in the SQL Server query optimizer. Can I still ...
7
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2answers
313 views

Index that is not used, yet influences query

I've got a PostgreSQL 9.3 table with some numbers and some additional data: CREATE TABLE mytable ( myid BIGINT, somedata BYTEA ) This table currently has about 10M records and takes 1GB of ...
7
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1answer
2k views

Query plan cache bloated by ad-hoc queries, even with “Optimize for Ad-hoc Workloads”

I've been noticing what I thought to be unusual issues with our query plan cache, where the plans in the cache were never more than a day old. Through running the following query (courtesy of ...
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10k views

PostgreSQL Sequential Scan instead of Index Scan Why?

Hi All I've got a problem with my PostgreSQL database query and wondering if anyone can help. In some scenarios my query seems to ignore the index that I've created which is used for joining the two ...
7
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1answer
108 views

Two servers, different execution plans. Several orders of magnitude difference in run time

Two servers, Development and Live. Live server is an Amazon RDS SQL Server Web instance. Both servers have identical schema and data. There is a good spatial index on the geometry column. On my ...
6
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4answers
3k views

How can I remove a bad execution plan from Azure SQL Database?

DBCC FREEPROCCACHE doesn't work in Azure SQL DB. How else can I force a plan to kick itself out of the cache in a way that won't hurt a production system (i.e. I can't just go alter tables willy ...
6
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2answers
541 views

Correlated subquery and join: still the same exectution plan?

I have a correlated subquery like this (from BOL): SELECT DISTINCT c.LastName, c.FirstName, e.BusinessEntityID FROM Person.Person AS c JOIN HumanResources.Employee AS e ON e.BusinessEntityID = ...
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300 views

SQL Server changes execution plan - Part 2

Previous question: SQL Server changes execution plan We are using SQL Server 2014 Developer Edition. SQL Server changes execution plan on identical query and the same database and SQL Server (I ...
6
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2answers
798 views

Query Plans not retained insufficient memory errors

We have been experiencing memory issues with SQL Server. We first realised we had a problem when we started getting timeouts and login errors: A connection was successfully established with the ...
6
votes
1answer
458 views

Why does the plan cache contain estimated and not actual execution plans?

I can think of many reasons behind this decision of storing estimated plans in the plan cache and not the actual plan. But I can't find the "correct" answer.
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3answers
115 views

Query wont compile/run

I have a query that won't run on the production server but it runs on the test server. It seems like the query plan won't compile or its compiling a very bad query plan. I have updated all statistics ...
6
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1answer
1k views

Index seek much slower with OR condition compared with separate SELECTs

Based on these questions and the answers given: SQL 2008 Server - performance loss possibly connected with a very large table Large table with historical data allocates too much of SQL Server 2008 ...
6
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2answers
116 views

how to get estimated subtree cost?

If I have a query that returns a query_plan, for instance like this: SELECT TOP 1000 st.TEXT ,cp.size_in_bytes ,cp.plan_handle ,QP.query_plan FROM sys.dm_exec_cached_plans AS cp CROSS ...
6
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2answers
1k views

“Recheck Cond:” line in query plans with a bitmap index scan

This is a spin-off from comments to the previous question: Postgres 9.4.4 query takes forever Using PostgreSQL 9.4, there always seems to be a Recheck Cond: line after bitmap index scans in query ...
6
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2answers
328 views

Unexpected Implicit conversion in a procedure

I have a procedure like this (simplified): CREATE PROCEDURE test @userName VARCHAR(64) SELECT * FROM member M INNER JOIN order O ON M.MemberId=O.MemberId WHERE M.Username = @userName There is a ...
6
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2answers
4k views

How do I get the execution plan for a view?

I have a schema with a number of views. I need to check the execution plans to make sure the appropriate indexes are in place and being used. How do I do this? I'd rather not have to copy and paste ...
6
votes
1answer
145 views

Set statistics I/O for nested loops

Consider the below query: CREATE PROC dbo.GetPage @orderid AS INT = 0, -- anchor sort key @pagesize AS BIGINT = 25 AS SELECT TOP (@pagesize) orderid, orderdate, custid, empid FROM ...
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1answer
2k views

Storage order vs Result order

This is a spin-off question from Sort order specified in primary key, yet sorting is executed on SELECT. @Catcall says this on the subject of storage order (clustered index) and the output order ...
6
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1answer
92 views

Why is DistinctSort followed by TopNSort in my query plan?

I have the following definition: CREATE TABLE [dbo].[JobItems] ( [ItemId] UNIQUEIDENTIFIER NOT NULL, [ItemState] INT NOT NULL, [ItemCreationTime] DATETIME ...
6
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1answer
153 views

PostgreSQL partial index unused when created on a table with existing data

In PostgreSQL 9.3, I am attempting to create an efficient index on a rarely-used (0.00001% of total records) boolean column. To that end, I discovered this post on SO: ...
6
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1answer
2k views

Optimize for ad-hoc workload

I know what this option does and how to enable it. My question is what things will happen if I were to enable this. Without giving too much info, our accounting system is a Microsoft Dynamics ...
6
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1answer
3k views

Why does it take so long to calculate an Execution Plan?

One of our customers has just upgraded to a new server. For a particular stored procedure the first time you execute it, is taking over three minutes to run. Subsequent runs are less than 1 second. ...
6
votes
1answer
80 views

Why does assigning FOR XML to an XML variable warn about CONVERT_IMPLICIT(XML)?

SET STATISTICS XML ON; DECLARE @x XML = (SELECT 'hi' "@id" FOR XML PATH ('this'), root ('xml')); Type conversion in expression (CONVERT_IMPLICIT(xml,[Expr1001],0)) may affect ...
6
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1answer
239 views

Are database query optimizers aware of storage performance differences?

As I understand it, the query optimizer in SQL Server (or any other RDBMS, really) isn't aware of the performance of the storage underneath the database, and will make decisions as if all storage has ...
6
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1answer
387 views

Capture Complex Actual Execution Plans

I have a stored procedure that among other things builds and executes a large number of Dynamic SQL statements. (Don't hate me, I didn't write it.) I would like to retrieve the actual execution plan ...
6
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2answers
101 views

Fixed query plan for a stored procedure

I am exploring the plan guides topic. Sounds easy, as far as we go through the examples in documentation. The problem is that I cannot find any working example (nor did I manage to figure it out by ...
6
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0answers
180 views

Need help understanding query plan: estimates vs. actuals [closed]

I'd like to understand a section of the query plan that seems to mess up my query. The picture shows that there's a clustered index seek, followed by compute scalar, followed by sort. The part ...
5
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2answers
166 views

Running query against DMVs for Query Stats and Execution Plans joined to sys.databases

I originally posted this as a different question in Twitter #sqlhelp, but wanted to post it here differently. I'm trying to create a job that tracks worst performing statements for various statistics ...
5
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4k views

Should I refresh query plan cache

Please let me explain my problem and situation: I have a web application - MVC3, MSSQL Server 2005, LinqToSQL. It has been running great until one fine morning I pushed a lot of rows to a table that ...
5
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1answer
2k views

SQL Server, TOP versus ROW_NUMBER

I'm learning about Execution plans and am trying out different queries and comparing their performance and stumbled upon this: SELECT StatisticID FROM ( SELECT StatisticID, ROW_NUMBER() OVER ...
5
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4answers
1k views

View locks acquired during query execution (SQL Server)

Query execution plan does not show the locking details by default, is it possible to view the locks, along with the type, acquired during the execution of a query?
5
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3answers
4k views

SQL Server 2005 get execution plan of a overnight stored procedure

There is a overnight job runs long time. I have used profiler to get the trace and identified a statement (in a stored procedure) that takes most of execution time. Now I need to see the execution ...
5
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3answers
77 views

Clustered Index Scan when using greater than in WHERE clause

I have the following table create table t1( col1 varchar(255) NOT NULL, col2 varchar(255) NULL, col3 bigint NULL, CONSTRAINT PK_t1 PRIMARY KEY CLUSTERED ( col1 asc ) ) CREATE NONCLUSTERED INDEX ...
5
votes
1answer
462 views

how to improve performance by using or not using table variables

I have a table variable: DECLARE @to_process TABLE ( [Id] [bigint] NOT NULL, [SequenceId] [bigint] NOT NULL, ... ) INSERT INTO @to_process ( Id , SequenceId ... ) SELECT ...
5
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1answer
179 views

Understanding below execution plan

I have two tables tb1 and tb2, tb1 doesn't have any indexes on it. I populated tb1 with 1000000 rows and tb2 has 500 rows in it and with a clustered index on ID column. To understand nested loop ...
5
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2answers
124 views

Joining two subqueries with union all and join leads to suboptimal execution plan

I've faced the similar problem on my production environment, but I managed to reproduce this behavior on Northwind DB. Consider the following query: USE NORTHWND; DECLARE @ids TABLE ( Id NCHAR(50) ...
5
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1answer
178 views

When does an execution plan not show in sp_WhoIsActive?

I use Adam Machanic's excellent sp_WhoIsActive procedure to see activity and to log to a table to troubleshoot long running queries. Why does the execution plan not show all the time in the results? ...
5
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2answers
91 views

looking for missing indexes in the cached execution plans

I have the following query that shows me what is cached in sql server: SELECT cp.objtype AS ObjectType, OBJECT_NAME(st.objectid,st.dbid) AS ObjectName, cp.usecounts AS ExecutionCount, st.TEXT AS ...
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1answer
811 views

A possible infinite recompile was detected for SQLHANDLE

I have been finding strange error messages on the sql error log: Bocss: same deadlock taking place every hour – needs investigating Also lots of recompiles are listed in the error log for other ...
5
votes
1answer
735 views

Execution plan using B+ tree index, but also sorts

I'm using Oracle sqlplus. And I have the following query: SELECT fooID from foo MINUS SELECT fooID from bar; I have created two unclustered B+ tree indexes. One in the field fooIDof the table foo ...
5
votes
3answers
154 views

Cardinality Estimator Question after 2014 SP1 + CU4 Upgrade

We recently upgraded from SQL Server 2008R2 to SQL Server 2014 SP1 + CU4. After a couple of weeks, there were problems with execution plans not properly estimating row counts. The problem got so bad ...
5
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1answer
1k views

Query Plans Change Performance Worse in SQL Server 2014

We recently upgraded our server from SQL Server 2008R2 to SQL Server 2014. We have a query that ran fine in 2008R2 but now in 2014 runs incredibly much slower and has a bad execution plan. I've done ...
5
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3answers
436 views

Parallel Plan Selection

I have a weird query plan problem. I have two databases (Let's call them DB1 and DB2) where both are sitting in the same SQL-Server instance and have identical schema. In there, we have a couple ...
5
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2answers
101 views

Is execution plan cached “better” for stored procedures than for a non-dynamic query?

Reading different explanations about execution plan caching by Microsoft SQL Server, I'm confused about the benefits of using stored procedures instead of non-dynamic queries. By a non-dynamic query ...
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4answers
3k views

When is a full table scan better than index scan?

What are some scenarios (in SQL Server) in which a full table scan is better than an index scan?