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

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4
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1answer
137 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 ...
4
votes
1answer
964 views

SQL Server 2008 query planner failing after index drop & recreate

Recently we ran a script to our production DB that would dynamically drop and recreate hundreds of indexes as filtered indexes. While this script had run perfectly in all other previous tests, now ...
3
votes
3answers
895 views

How does NHibernate handle execution plan?

I heard from a podcast that there are no ORMs that have a good solution for execution plan reuse. It will lead to increased execution plan cache which affects the performance. How does NHibernate ...
3
votes
2answers
106 views

Changing metadata changes query output issue [duplicate]

Recently stumbled across the following problem: changing metadata changes query output. Here is how to get it. CREATE TABLE [dbo].[prod] ( [ID] [tinyint] NOT NULL, [values] [tinyint] NOT NULL ) GO ...
3
votes
1answer
1k views

Clustered Index Update on Nonclustered Columns

Using: SQL Server 2008 R2 I am currently stepping through a query execution plan, and have come across an instance of a clustered index update on a table. The issue here is that the columns that are ...
3
votes
1answer
333 views

How to determine cause of runtime increase given two query plans with SpillToTempDb warning

Two actual query plans were captured for two executions of one query: Plan "Fast" took ~1s and occurs about 90% of the time. Plan "Slow" took ~16s. Since the graphical plans look ...
3
votes
1answer
132 views

Do operations on indexed views happen in parallel?

When I'm inserting into a table that has a view with a clustered index, the estimated execution plan appears to do the table insert and the view's clustered index insert operations in parallel. Is ...
3
votes
2answers
214 views

Multicolumn statistics on large table yielding poor estimations

I have a rather large table (~200 million rows), and although the statistics are up to date using WITH FULLSCAN, is it possible that my histogram (limited to 200 steps) is simply too broad for the ...
3
votes
1answer
83 views

Every query plan statistic says my query should be faster, but it is not

I have a bit of a odd situation. I have two queries that produce the same result, according to SSMS and SQL Sentry Plan Explorer the first query should cost 95% and the 2nd query should cost 5%. ...
3
votes
2answers
1k views

SQL Query too slow on SUM function

I've a table with around 32 million rows having clustered unique index on CountryID,RetailerID,ProductID,DateID,EventID,TypeID and query is SELECT f.RetailerID , TypeID ...
3
votes
1answer
303 views

How are foreign keys resolved when creating tables in batch?

I am creating a database version management tool with the goal of being able to recreate a database from scratch using text/sql files contained in source control. As part of establishing a baseline ...
3
votes
1answer
109 views

can sql generate a good plan for this procedure?

I have read that procs that do not always do the same thing per se, will not always have a good plan generated. That is (correct me if I'm wrong), if I have a proc that if the day is even it reads ...
3
votes
1answer
133 views

Why does my query end up with two seeks instead of one and how do I fix that?

I have these two tables: CREATE TABLE [TaskItems] ( [ItemId] UNIQUEIDENTIFIER NOT NULL UNIQUE PRIMARY KEY, [LastOperationTime] DATETIME NULL DEFAULT GETUTCDATE(), [OwnerId] ...
3
votes
1answer
207 views

Optimizing complex join predicates [closed]

Table Definitions CREATE TABLE [dbo].[Pin_Mtg] ( [MtgId] bigint NULL, [CntyCd] char(5) NOT NULL, [BatchDt] int NOT NULL, [BatchSeq] int NOT NULL, [MtgSeq] tinyint NOT NULL, ...
3
votes
1answer
675 views

Non-Clustered Index key columns to cover a variable where clause

To whoever reads this, sorry for the long question and thanks so much for your time. I'm needing some help on understanding what columns should be key/non key in the following situation, and what ...
3
votes
1answer
94 views

Simple SELECT takes forever, but works as a subquery. Why?

I'm running a MySQL 5.1 server and I have a MyISAM table called my_table with nearly 5 million records. Its structure is the following: ...
3
votes
1answer
501 views

Execution plan in simple query in PgSQL depends on offset clause, why?

Update on 2013-01-16 11:08: see below I am working on PostgreSQL 8.4.14 with the following table fed with 53k lines: CREATE TABLE botany.taxon_data_cache ( taxon_id int NOT NULL, ...
3
votes
1answer
914 views

View SQL 2008 sp_cursorexecute Underlying Query and Execution Plan

I'm performance tuning a Dynamics AX application and see in a SQL trace a long-running, high-I/O query of the form exec sp_cursorexecute 1073742882 ... When I try and run that query in a new SQL ...
2
votes
4answers
1k views

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

DBCC FREEPROCCACHE doesn't work in SQL Azure. 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 nilly)? ...
2
votes
2answers
76 views

On which server does a query execute?

Given two Microsoft SQL servers: Say ServerA has a view titled "View1": SELECT * FROM ServerB.database.dbo.Table1 WHERE Column1 IN (1,2,3) and a stored procedure "sp_Foo": SELECT * FROM View1 WHERE ...
2
votes
1answer
112 views

Execution Plan not matching Stored Proc

Below is a stored proc to count the number of widgets made in a month. If no widgets are made, no records will exists. The execution plan shows an INNER JOIN of the M and A tables, where in the ...
2
votes
1answer
3k views

What I can do to speed up Key Lookup in my Query

I am using SQL2005 and against them I calling query simila to this declare @art table (id int primary key, naziv varchar(35) null, sifra varchar(15) null, jm int null); insert ...
2
votes
1answer
236 views

How do you figure out what planner cost constants to use in Postgres?

I'm using Postgres 8.4 right now. Performance has started to become an issue as our tables have grown in size and our queries in complexity, so I've started to look into some performance tuning, but I ...
2
votes
1answer
152 views

Is there any way to save the execution plan in a file in PostgreSQL?

By saving a plan in a file, I don't mean to view it, but force the optimizer to use the saved plan to execute some query. For example, if the optimizer chooses to do a hash join for a two-table ...
2
votes
1answer
1k views

SQL Server 2008 R2 sys.dm_exec_sql_text question

If i run the following query on our production server: SELECT DISTINCT TOP 10 t.TEXT QueryName, s.execution_count AS ExecutionCount, s.max_elapsed_time / 100000 AS MaxElapsedTime, ...
2
votes
2answers
833 views

Why is query using Clustered Index when it shouldn't?

Let us presume I have a table named Category in a SQL Server 2005 database. Category has category_id (bigint, identity) as its primary key and name (nvarchar(50)). There is obviously a clustered ...
2
votes
1answer
298 views

Postgres planer JOIN removal

I have two tables, one contains a lot of rarely update data, and one contains a little of frequently update data. Every record in second table has corresponding record in the first, like following: ...
2
votes
1answer
94 views

Understanding SQL Server plan cache

I've been reading about the SQL Server plan cache and optimizing for adhoc workloads, etc. I'm fairly new to the topic and have a few general questions to help paint a better picture: Suppose I have ...
2
votes
1answer
956 views

Fast paginated result, for various filter clauses

I have been working on obtaining a paginated result from a table in my database (11g). While I have a query that does work (ie, the result is correct) it does not perform as well as I'd like to and I ...
2
votes
3answers
3k views

Revert to old plan in Oracle

A weekly, scheduled, schema wide stats update was run on our Oracle 11R2 RAC cluster on Sunday. One of the queries had no apparent data or code change but now runs at 3 hours instead of 20 minutes. ...
2
votes
1answer
767 views

Is it correct, order of where clause doesn't matter when it is used with join?

I have question on execution of queries in which join is used with where clauses. I read this question on join with where conditions. I tried options like disabling rules and checked actual query ...
2
votes
2answers
940 views

In DB2, how can I disable NLJOIN?

I want to indicate to the optimizer, via SET or optimization profiles, that NLJOIN shouldn't be used at all when optimizing a query. I've been looking for this for a while without any success. I ...
2
votes
1answer
59 views

Monitoring the Postgres query parser

As I understand it, when you send a query to Postgres like: SELECT id FROM table1 WHERE name = $1; Postgres will create a query plan. The plan will be cached for the same query in the same ...
2
votes
1answer
58 views

Understanding the simple execution plan in PostgreSQL

I'm new to execution plans still trying to learn. My problem is for below query select * from item limit 3; I got following execution plan, "Limit (cost=0.00..0.07 rows=3 width=75)" ...
2
votes
1answer
430 views

Non-clustered Index Update not displayed in execution plan [duplicate]

Possible Duplicate: Nonclustered Index Insert I'm trying to work out the cost of having a nonclustered index on a particular table, but I don't see any maintenance cost in the execution ...
2
votes
1answer
256 views

Query tuning - SQL Server

One of our developers are trying to run the below query on a development server, which involves pulling data from a linked server, production. The query ran for more than 14 hours before it was ...
2
votes
2answers
498 views

Clustered monotonically increased index insert performance

I have a table with field Id (bigint, IDENTITY) as primary key and clustered index on it. I inserted 400 rows and saw execution plan. I got: the relative query cost for this insertion 36% and for this ...
2
votes
1answer
670 views

Is there any difference on performance when choosing DISTINCT or GROUP BY to bring distinct values?

I would like to know if there is any difference concerning performance when choosing DISTINCT or GROUP BY to bring distinct rows from a query. I've tried comparing the execution plans, but they seem ...
2
votes
1answer
330 views

Does a change in a query executed with sp_executesql cause recompilations?

I am experiencing a lot of re-compilations in my database. Most of the queries being executed are simple queries and all of them are being executed using the sp_executesql stored procedure. ...
2
votes
2answers
129 views

SQL Server doesn't use expected index

I have the following query (simplified from an Entity Framework query, I don't have direct control of the SQL): SELECT TOP 15 HouseHoldingRuns.Id, ( SELECT TOP 1 ManCoId FROM ( SELECT TOP ...
2
votes
1answer
130 views

High I/O for part of query

I have a large query that I'm trying to tune. I write lots of queries but haven't done a lot of tuning. I've included a screenshot from SQL Sentry Plan Explorer Free (SSPEF): In the above part of ...
2
votes
0answers
93 views

Multi-Statement Template Plan Guide

A piece of, um, software seems to be issuing ~20k queries of this form every few seconds: DELETE FROM macVendor WHERE companyId=N' 08-00-'; INSERT INTO macVendor (companyId,organization) VALUES (N' ...
2
votes
0answers
48 views

Identical query & instance but other execution plans & performance [duplicate]

I have 2 identical queries . One is executed with parameters, the other is executed with hardcoded values. Somehow sql server is creating 2 different execution plans for the 2 queries. The first one ...
2
votes
0answers
325 views

Oracle 11g bug ? not returning the record until I triggered index to invisible and then to visible

We are using Oracle 11g, 11.2.0.3. We know a record exists in a table but a select is not returning it for some odd reason. The execution plans the general query, not forcing any index, shows that ...
1
vote
1answer
170 views

Understanding execution plans using TVPs

I have some slow running queries (8 seconds across 1M records grouped by months) and have been trying to make sense of the execution plans. We use around 10 TVPs to send in a set of filters that the ...
1
vote
2answers
779 views

Updating a table efficiently using JOIN

I have a table that has the details of households and another that has the details of all the persons associated with the households. For the household table I have a primary key defined using two ...
1
vote
1answer
119 views

Estimated rows very wrong when using declared variables

I am getting very, very wrong estimates for the clustered index seek step of this query (estimated rows is 8,637,530; actual is 74,723): Declare @StartDate as date = '10/1/2014'; Declare @EndDate as ...
1
vote
3answers
2k views

Why would recompile query hint result in different plan for same adhoc statement after freeproccache?

This is on SQL 2005 SP2, but I suspect this is something that applies to all query hints in general. I've got an adhoc sql statement that gets a different query plan solely because of ...
1
vote
1answer
88 views

Query Plan Different When Using Compiled Values

I have pulled out an execution plan from the plan cache and from the XML pulled out the compiled values. Then I have run the query in SSMS using the compiled values and the query plans are different ...
1
vote
1answer
203 views

Relative cost of two similar queries involving XML columns

I have two queries as shown below which do the same thing. Here xmlcolumn is a column with datatype XML. I use these queries to search for a string anywhere in the XML column. I checked the execution ...