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

learn more… | top users | synonyms (1)

0
votes
1answer
189 views

Simple select query taking too long

I have been having a hard time with this query, I have a webpage which is supposed to run this query a dozen of times, and with an execution time up to 40 - 50 seconds per query, you can see how this ...
0
votes
3answers
76 views

MySQL optimizer won't use my index

With the following query: SELECT * FROM geoname LEFT JOIN alternatename ON geoname.geonameid = alternatename.geonameid AND alternatename.isPreferredName = 1 AND ...
1
vote
1answer
21 views

DB2 LUW: how to influence query planner's choice of join

Suppose I have two tables, A and B. They "share" the same primary key, which is indexed in both tables. Table B also has a timestamp column which is separately indexed. I do a subselect on B using ...
1
vote
2answers
95 views

deteriorating stored procedure running times

I have a stored procedure that is executed by my web application. Today, when an end user started an operation that affected more rows than usual, I started getting calls that the wait times for the ...
5
votes
1answer
155 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? ...
0
votes
2answers
38 views

Non Clustered Index Scan Properties window - Predicate order different than query order

SQL 2012 Data Warehouse type environment... I have a Non Clustered Index on a Type 2 Dimension table, which I'll just call DimStudent. The index is defined as below, with data types and other info ...
8
votes
2answers
149 views

Why is TOP operation in SQL execution plan

After searching for a while, I decided to post this question for lack of finding an answer and apologize if there is a similar question/answer out there. When running the query below on two similarly ...
1
vote
0answers
32 views

Reasons why plans of sys.dm_exec_cached_plans do not match actual plans?

I re-assess index / query optimization and actually focus on key/bookmark lookpus that could be eliminated. Using a script of Jonathan Kehayas I go through the list of query plans that used those ...
2
votes
2answers
65 views

Understanding Execution Plan

I am really having hard time understanding the below execution plan. Query 1: (Simple Select Query) Record count of ##SALES_UNIT_RESULT is 168. In first execution plan it is fine. ;WITH ...
4
votes
1answer
80 views

DISTINCT ON vs ROW_NUMBER() for getting a row with a maximum value of a group

I have the following table in PostgreSQL 9.4: CREATE TABLE dpa( id serial NOT NULL, currency_id integer, amount numeric(14,3), date timestamp without time zone, plat_id integer, pl_id ...
0
votes
1answer
117 views

Optimizing queries vs. adding indexes

I have this very old and SLOW query that I am trying to optimize, but I am not sure I can do anything to it, but add more indexes on columns involved in WHERE, JOIN and ORDER BY. Query: SELECT TOP ...
7
votes
1answer
306 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 ...
1
vote
1answer
50 views

SQL Server execution plan is using PK instead of index

The following query is taking 5 seconds to return 9692 rows: SELECT Project.CalculateSequencialProject, Project.CreateDate, Project.OpeningDate, Project.ForecastClosingDate, ...
5
votes
2answers
79 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 ...
5
votes
2answers
117 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) ...
9
votes
1answer
156 views

Huge mismatch between reported index size and number of buffers in execution plan

The issue We have a query like SELECT COUNT(1) FROM article JOIN reservation ON a_id = r_article_id WHERE r_last_modified < now() - '8 weeks'::interval AND r_group_id = 1 AND ...
1
vote
3answers
97 views

Why does the query plan still sort a table despite having an index sorted on the columns?

I'm using Postgres 9.1 I have two tables I am joining: wikidb=> \d page Table "public.page" Column | Type | Modifiers ...
2
votes
1answer
871 views

query performance gains by removing operator hash match inner join

While trying to apply the contents of this question below, to my own situation, I am a bit confused as how I could get rid of the operator Hash Match (Inner Join) if any way possible. SQL Server ...
-2
votes
1answer
49 views

Allowing non-sysadmin users to see SQL Server execution plans

Is this possible ? On SQL Server 2012+, grant access to a non sysadmin user to see the execution plans ? And can this be done for selected databases only ?
6
votes
1answer
79 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 ...
5
votes
1answer
702 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 ...
7
votes
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 ...
2
votes
1answer
46 views

Oracle and execution plans

I have used the following procedure to view the last execution plan create or replace procedure display_plan as begin for c in (select plan_table_output t from table(dbms_xplan.display_cursor('', ...
1
vote
1answer
36 views

performance tuning queries - practice [closed]

I would like to find some materials and real life practice about performance tuning queries. Can anyone recommend some resources to read and study?
0
votes
1answer
37 views

Merge join turns to hash match when adding a 2nd join

I would like to educate myself on what goes on under the hood in SQL Server, so I'm about to delve into Grant Fritchey's book Dissecting SQL Server Execution Plans. As it's 181 pages I just wanted to ...
11
votes
2answers
799 views

Why does my WHERE clause benefit from an “included” column?

According to this answer, unless an index is built over the columns which are used to restrict, the query will not benefit from an index. I have this definition: CREATE TABLE [dbo].[JobItems] ( ...
4
votes
1answer
188 views

Index is not used with table inheritance

I have a PostgreSQL 9.0.12 database with a master table and 2 child tables. My tables: CREATE TABLE test2 ( id serial PRIMARY KEY, coll character varying(15), ts timestamp without time ...
8
votes
3answers
324 views

Lots of “FETCH API_CURSOR0000…” on sp_WhoIsActive ( SQL Server 2008 R2 )

I have a strange situation. Using sp_whoisactive I can see this: Ok, with this query, I can see what is triggering ( does this word exists in english? ) it: SELECT c.session_id, c.properties, ...
0
votes
2answers
54 views

Identical SQL Server databases hosted in the same physical DB server

We have hosted similar SQL Server 2014 databases TestDB and TESTDB_Copy on the same physical server. The two databases are almost the same and there may be minor differences in the number of records ...
3
votes
2answers
219 views

Any SQL where clause performance similar to where 1=0

(i'm using SQL Server 2008R2 or later) For centralize manage and consistent, there is a view definition as follow: CREATE VIEW view_all_situation ( select null as src, tf.col1, sum(col2) as fee, ...
6
votes
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 ...
3
votes
2answers
935 views

Use a view to join tables or a stored procedure for a better execution plan?

First let me state I am a C# developer, not a SQL Server DBA, so please excuse my ignorance on SQL Server database query execution plans. What I want to know is for a stored procedure which the ...
11
votes
1answer
1k views

SET STATISTICS IO- worktable/workfile

I am executiong query, that produces plan: Statistics IO: Table 'Worktable'. Scan count 0, logical reads 0, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob ...
3
votes
1answer
45 views

Execution plan for COMPUTE BY

I understand that the COMPUTE BY feature is deprecated. Out of curiosity I would like to know how the query processor executes a COMPUTE BY query. The execution plan does not contain any hint: How ...
2
votes
2answers
103 views

Execution plan has TOP operator for query without TOP or ORDER BY

I have product sales by month temporary table.(subset of much larger historical table) I'm running query to find new product not previously sold in the previous months for a specified 6 month range. ...
7
votes
1answer
105 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
votes
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 ...
1
vote
1answer
132 views

mysql query choosing an incorrect execution plan

I have a primary with an dependant subquery as a where condition that is choosing a wrong execution plan, and therefore is running for ever. Main query: SELECT rtr.id AS id156_, ...
9
votes
2answers
174 views

Why isn't the primary (clustered) key being used in this query?

I have a SQL Server 2008 R2 table whose schema structure looks as follows: CREATE TABLE [dbo].[CDSIM_BE] ( [ID] [bigint] NOT NULL, [EquipmentID] [varchar](50) NOT NULL, [SerialNumber] ...
3
votes
0answers
97 views

Bad Plan after a couple of days

I have this query that runs fine for a couple of days (from the application) and then slows down to where it can't even finish. If I rebuild the plan, it flies. There is a signifigant amount of data ...
4
votes
1answer
114 views

Should I use a subquery to help SQL Server find the correct plan

I have a query (which has components which are built on the fly depending on the selections a user makes in the interface) that runs in SQL Server 2008-R2 that runs in about 100 databases. Users are ...
10
votes
1answer
179 views

Why is the secondary selective index not used when the where clause filters on `value()`?

Setup: create table dbo.T ( ID int identity primary key, XMLDoc xml not null ); insert into dbo.T(XMLDoc) select ( select N.Number for xml path(''), type ) from ( ...
5
votes
1answer
976 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 ...
1
vote
1answer
297 views

Algorithm used to perform offset/limit over a union all result set

I have two result sets: rs1: id name serial text ________________ 1 Nick .................... 1233112 Pete rs2: id name serial text ...
1
vote
1answer
81 views

Postgres not using the index even when rows returned is 5% of the table

I have a postgres table with the following structure: +---------+-------------+-------------+----------+---------+---------+ | id | timestamp | numvalues | text1 | text2 | text3 | ...
12
votes
2answers
3k views

Trace Flag 4199 - Enable globally?

This may fall under the category of opinion, but I'm curious if people are using trace flag 4199 as a startup parameter for SQL Server. For those that have used it, under what circumstances did you ...
2
votes
3answers
83 views

SQL actually executed as planned in ORACLE?

I wonder if SQL is definitely executed as execution plan. I mean.. is the actual SQL execution process always consistent with execution plan, i.e. does the same SQL always give the same plan?
13
votes
1answer
310 views

SQL Server recreating plans each day

We have this problem in our production environment. Microsoft SQL Server 2008 R2 (SP1) - 10.50.2500.0 (X64) - Enterprise Edition (64-bit) on Windows NT 6.1 (Build 7601: Service Pack 1). SQL Server ...
1
vote
1answer
111 views

Another bad execution plan!

This is running SQL Server 2012 SP2 Enterprise Edition. I have a nightly ETL job that, for a specific SP, is taking way too long to run. During my investigation I found that it was a specific update ...
8
votes
2answers
209 views

Getting a realistic query plan when partitioning with low volumes of data

We're using partitioning to reduce the amount of blocking our OLTP system experiences due to locks, with a partition scheme that splits the working tables into 100 partitions based on a customer id. ...