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

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3
votes
1answer
236 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 ...
0
votes
0answers
36 views

Analize Query in MySQL Server 5.1

I try use MySQL Workbench 6 to analyze the cost, but they don't show the cost of query. How i get this costs?
7
votes
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 ...
2
votes
1answer
517 views

Does SQL check each And condition if first condition fails? [duplicate]

For a query of below kind does sql process data for each And condition if first And condition fails? If Emp_ID is not 12 for a row then does it check condition of Emp_Name? So how SQL process this ...
12
votes
1answer
391 views

How deterministic is execution plan creation in SQL Server?

Given the following constants: The same database with the same structure (tables, indexes, etc) The same data The same SQL Server and hardware configuration The same statistics The same SET options ...
6
votes
2answers
1k views

Why is my plan guide not being used?

We recently ran into the tipping point issue and some of our report queries that used to complete execution within a couple of seconds are now taking more than 2 min because the query optimizer simply ...
3
votes
1answer
203 views

How do I deal with query getting slower when a select parameter is not specified inline?

I faced this problem twice with SQL Azure and two different queries so far. Something like this: select top(100) * from SomeView WHERE AccountId='actual-guid-typed-in-here' runs super fast but ...
0
votes
1answer
417 views

Oracle 10g: same query, different plans on copies of the same DB

I have a query joining a number of long tables (primary key in one table, indexed column in another) which results in different plans on different copies of the same database. The structure of copies ...
4
votes
1answer
185 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
1answer
1k views

Is there any way to get the estimate cost of executing a query in MySQL?

In PostgreSQL, EXPLAIN or EXPLAIN ANALYZE will show the estimate cost of executing a query. But EXPLAIN in MySQL doesn't provide this information. How can I get the estimate cost without installation ...
0
votes
1answer
77 views

Fetching User Recent Status

I am running mysql with MyISAM storage engine to store user status(user updates data). To load user recent updates data i am using this query: $limit = 20; $uid = 3; SELECT * FROM userstatus WHERE ...
3
votes
1answer
450 views

SHOWPLAN does not display a warning but “Include Execution Plan” does for the same query

I was running the following query in SSMS and it showed me a warning in the "Include Execution Plan" window select CLIENT_GUID, PMT_AMOUNT, DATE_COMPLETED from ( select payment.CLIENT_GUID, ...
0
votes
1answer
73 views

Access and filter in oracle plan

I came to a execution plan where oracle choose to access the index but instead of using the columns as predicate it only filter by them. My question is what are the reasons that can cause that(all ...
0
votes
1answer
339 views

Comparing execution plans [closed]

How does the optimizer compare different execution plans of the same query? Let's say we have two complex and structurally different execution plans, how can I know if they are providing the same ...
1
vote
1answer
243 views

Understanding MySQL's 'explain'

I have following query with explain: mysql> explain select dd.data from dane dd join test1.tag1 t1 on dd.id = t1.id join test1.tag2 t2 on dd.id = t2.id join test1....
2
votes
2answers
2k views

Estimated vs Actual Number of Rows

I have 5 tables that contain data split by quarter each table has a similar structure to the following: ID_Column bigint PK, EventType int, DateStamp datetime PK CustomerId int, ARG_1 nvarchar(32), ...
8
votes
1answer
873 views

Re-run a specific actual query plan

I have captured an actual query plan for a specific query. After this I've changed a few things around (including updating the statistics) and re-ran that specific query. Now the actual query plan ...
2
votes
1answer
564 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 ...
4
votes
2answers
698 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 ...
2
votes
0answers
249 views

Does Oracle ADO.NET varchar parameter size influence query plan reuse?

I am considering to apply a fix which will generate constant parameter sizes for (n)varchar parameters. The application is based on NHibernate with the old OracleClientDriver (using Microsoft Oracle ...
2
votes
0answers
163 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' ...
6
votes
1answer
396 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 ...
4
votes
1answer
1k 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 ...
2
votes
0answers
51 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 ...
4
votes
1answer
401 views

Why clustered index scan?

I just started to learn to optimize my queries and to analyze their query plans. I thought this query would generate nonclustered index seek + key lookup. SELECT ct.* FROM Person.ContactType AS ct ...
3
votes
1answer
122 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 ...
1
vote
0answers
99 views

What to look for in query execution plans? [closed]

Assuming the query execution is slow, I have collected the xml plan. What should I look for in the actual execution plan. What are the top 10 things I need to watch out for? I know this is a broad ...
3
votes
1answer
130 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: +---------------------------------------------------------------...
8
votes
1answer
433 views

Does SQL Sentry Plan Explorer count the reads in UDFs?

I have a query like this: select dbo.fn_complexFunction(t.id) from mytable t In SQL Sentry Plan Explorer, I noticed I have to run Get Estimated Plan in SQL Sentry to make the Query Plan include the ...
4
votes
1answer
2k views

How bad is query plan pollution (too many equivalent plans in cache)?

Question currently affects C#/.NET, DB access based on ADO.NET and SQL Server 2008 R2, but I think it applies to other databases as well. I noticed some old modules of a system have non-optimal SQL ...
1
vote
1answer
244 views

Estimating a Size of Joining a Relation with itself

I'm studying size estimation of logical query plans in order to select a physical query plan. I was wondering what is the size of joining (natural join) a relation to itself? e.g R(a,b) JOIN R(a,b)
1
vote
1answer
7k views

Different execution plan for the same query if I change a value in the predicate

I am getting two different execution plans for the same query only by changing the value in the predicate, the first one uses nested loops and the other one hash join which takes a lot longer. ...
0
votes
1answer
379 views

SQL Server Index Scan Actual Executions

I have a fairly complicated query and running it on two databases with same schemas, but with different data produces different result. On database D1 the elapsed time is around 1 second, and the ...
5
votes
3answers
5k 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 ...
1
vote
1answer
104 views

A query executed in a backup of a database is performing better than if executed in the original database

We have two databases with the same data, let's call it Database A which is the original and Database B which is the backup from Database A. A query is performing much better in Database B for example ...
2
votes
0answers
260 views

Postgres - Partitioning old tables, partition query planning, optimisation

I've been trying to optimise our database, but not being a DBA and not having done a whole lot of tuning before I'm struggling a little with "too many options". I've already run pg_tune and bumped a ...
1
vote
2answers
2k views

Improve performance with the WHERE NOT IN sub-select clause

In the following query, I have to count transactions for each customer. [EDIT]However, I have to exclude from the result set entirely, customers that have a transaction older than one year. ...
3
votes
1answer
245 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, [...
2
votes
2answers
1k views

How can you tell when a query plan reuse is causing performance problems

When investigating a performance issue, a workmate suggested running DBCC FREEPROCCACHE to clear the plan cache. He came to this conclusion after noticing performance improved after a reboot. This ...
17
votes
4answers
992 views

Execution plan vs STATISTICS IO order

SQL Server graphical execution plans read right to left and top to bottom. Is there a meaningful order to the output generated by SET STATISTICS IO ON? The following query: SET STATISTICS IO ON; ...
3
votes
2answers
4k 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 ...
11
votes
2answers
8k views

How to optimise T-SQL query using Execution Plan

I have a SQL query that I have spent the past two days trying to optimise using trial-and-error and the execution plan, but to no avail. Please forgive me for doing this but I will post the entire ...
10
votes
2answers
3k views

When does sp_executesql refresh the query plan?

You'll have to forgive my naivety as I'm not a DBA but my understanding is that over time the statistics of a database change and a stored procedure must be recompiled to keep the query plan up to ...
3
votes
2answers
5k 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 ...
5
votes
2answers
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 ...
6
votes
0answers
181 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 ...
6
votes
2answers
822 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 ...
2
votes
1answer
661 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
283 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 ...
2
votes
2answers
83 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 ...