Comments on: SQL SERVER – Execution Plan – Estimated I/O Cost – Estimated CPU Cost – No Unit

By: Brn

Brn — Thu, 11 Apr 2013 20:45:48 +0000

Hi sir
My question is about avg_user_total_cost in stored procedure. I tune stored procedures and I realized that avg_user_total_cost had some different value. e.g 66,22 or 999,12 etc. How can I or a computer calculate that value? And What is the maximum value of avg_user_total_cost? Could you explain me ?
Thank you so much.

By: SQL SERVER – Weekly Series – Memory Lane – #013 « SQL Server Journey with SQL Authority

Sat, 26 Jan 2013 01:31:28 +0000

[...] Execution Plan – Estimated I/O Cost – Estimated CPU Cost – No Unit During the SQL Server Optimization training, I enjoy teaching Execution Plans Following are some common questions related to costs: [...]

By: samah

samah — Tue, 25 Dec 2012 18:31:29 +0000

I want quick answer to my question please

I apply a query using sql server 2012 and enforce it to executed with some test indexes but in the all cases i have different i/o cost and elapsed time

BUT the cpu time was constant for one query with different indexes it didnt change WHY??

When I work with a different query it give new cpu cost but also it still constant for the same query when i use different indexes type

By: Courage Dog

Courage Dog — Tue, 06 Nov 2012 14:53:05 +0000

I would call this exection plan unit “Gatez” (in short: Gz). So for example a query has 0.3 CPU Gz and 0.8 I/O Gz.
1 CPU Gz means one SQL Server executes one query for one moment.
1 I/O Gz means one SQL Server reads one portion of data for one moment.

By: nawed

nawed — Sun, 17 Jun 2012 11:58:57 +0000

How is speed mismatch handled between CPU and I/O unit ? Explain

By: jyoti

jyoti — Fri, 15 Jun 2012 08:19:01 +0000

Hello Pinal,
In which situation following type of error can occur in sql :-
“The query has been canceled because the estimated cost of this query (830) exceeds the configured threshold of 300.”

By: HARI

HARI — Wed, 16 May 2012 04:58:33 +0000

Hi Pinal. How can we write TSQL queries that take benefit of parallelism/multiple processors that are available on a production environment.

By: Scott Ellis

Scott Ellis — Tue, 03 Apr 2012 14:18:45 +0000

I am wondering if anyone knows if there is a way to check the estimated cost of a query before running it, and then return that value as a variable so that, if it is too high, I can elect to prevent certain queries from executing?

By: sunil pal

sunil pal — Thu, 23 Feb 2012 08:55:39 +0000

great knowlege i get regarding execution plan

By: Doug

Doug — Wed, 23 Feb 2011 16:21:43 +0000

Please see pauls whites blog on this —

The I/O cost of 0.003125 is exactly 1/320 – reflecting the model’s assumption that the disk subsystem can perform 320 random I/O operations per second

http://sqlblog.com/blogs/paul_white/archive/2010/09/01/inside-the-optimizer-plan-costing.aspx

By: Manjunath

Manjunath — Mon, 11 Oct 2010 16:52:05 +0000

Hi Darshan,

Thank you. But can you please let me know how other process can cause my current query execution Plan.

Regards,
Manjunath

By: Darshan Shah

Darshan Shah — Mon, 11 Oct 2010 15:10:53 +0000

Manjunath,
That is because of some other processes are going on your production server. That why execution plan is diifer then dev server.

Thanks
Darshan

By: keshav

keshav — Fri, 01 Oct 2010 20:52:10 +0000

Hi Pinal
I was looking your notes on performance tuning. I was very impressed after looking those.I am very new to SQL DBA. I have one question for you I just want to knowhow we can tune the stored procedures in sql server2005.
I was trying to tune the sp’s but I am able to change the indexes on the table. i can still see the higher i/o and CPU values. I can tune the sp’s upto some value but not more than that. I will be very helpful if you help me in this.

Thanks,
Keshav

By: Manjunath

Manjunath — Thu, 30 Sep 2010 19:14:53 +0000

Hi Pinal,

There is a Query.
If i run it on Production environment it takes around 6 mins if same i try to run on my DEV Server its taking more than an hour. can you please help me out. And also is there any way to compare two execution plans?

Thanks
Manjunath

By: steve

steve — Wed, 21 Jul 2010 22:15:05 +0000

Dear Pinaldave,

I came across the phrase: the total I/O was two logical reads in interpreting an actual execution plan. Could you please explain a bit about it?

Thank you in advance.

Steve

By: pinaldave

pinaldave — Tue, 25 May 2010 14:55:59 +0000

Sometime they will be and sometime they may not.

Usual case is they are same in most of the cases.

By: Lee

Lee — Tue, 25 May 2010 14:24:43 +0000

Pinal

I understand that “unit” has no predefined value. It may be 1 second, 1.5 seconds, or 4 years.

You said that the unit is used to compare different possible execution plans, and then chooses the plan with the lowest overall cost. For this to happen, obviously the unit, whatever it may be, has to be consistent between the different execution plans.

My question is that are these units consistent between entirely different statements? For example if I submit one query, which is very I/O intensive, and then 5 minutes later, on a different database connection, submit another query which is very CPU intensive, will the units for CPU and I/O be the same for both the queries (of course their numbers will be different)?

Thanks,
Lee

By: Marko Parkkola

Marko Parkkola — Sat, 27 Mar 2010 18:34:42 +0000

I can second that!

I’m working in a project where we have two almost identical databases, but not quite. One is used in development and one in testing. Dev-db is 100x larger than the test-db and dev-server is 10x more powerfull (more cores and memory).

Now if you go and just take execution plan from dev-db and then compare with execution plan from test-db you can get wildly different plans and wildly different estimations. Only way to be sure if optimizations works as planned is to set STATISTICS TIME ON and run the same query on both dbs.

By: Pinal Dave

Pinal Dave — Sat, 27 Mar 2010 16:05:21 +0000

Hello Juan,

As I write in article that these estimates should be used by us in the same way by which the SQL Server uses it – The estimate should be used to compare different queries with each other.

Regards,
Pinal Dave

By: Juan Carlos

Juan Carlos — Fri, 26 Mar 2010 15:53:37 +0000

All right, let’s no look for a unit or any other measurement. But how do I know if a given number is low or high. For example:
I/O Estimated Cost = 0.89874 is high or low?

By: Pinal Dave

Pinal Dave — Tue, 23 Feb 2010 16:15:22 +0000

Hi Abhijit,

The set statistics io result should not differ than the actual execution plan’s io cost. The estimated cost is just an estimation of SQL optimizer on the basis of data statistics and that may differ considerably if data statistics is not updated.

Regards,
Pinal Dave

By: Abhijit

Abhijit — Tue, 23 Feb 2010 07:29:33 +0000

Hi Pinal,
is it possible that
set statistics io will differ with the actual /estimated execution plan’s estimated cost?

By: ravikolli

ravikolli — Tue, 02 Feb 2010 22:34:11 +0000

Use can use

SET STATISTICS TIME ON

before the query and then

SET STATISTICS TIME OFF

and execute to know the exact time a query is taking to execute…

some times this helps with the comparition.

By: ROHAN

ROHAN — Sat, 30 Jan 2010 10:31:08 +0000

WHY WE USE COMPUTE

By: pinaldave

pinaldave — Sat, 23 Jan 2010 05:20:30 +0000

Marko,

Another great comment!