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Monday, March 26, 2012

Generation of estimated execution plan takes a long time

Hello,
I am puzzled by following problem. One of our tables has more than 12
billion rows. Usually, query plan and query itself is executed almost
immediately but occasionally, it take about 2 minutes to generate estimated
query execution plan for following query:
SELECT MAX(qwEventIx) FROM FTE_STREAM_EVENT (NOLOCK)
There is a PK clustered index defined on qwEventIx field. I do not observer
any blocking on this object when it takes a long time to generate estimated
query plan. There is a plan cached in syscacheobjects for this query.
I was wondering if anyone can explain why it takes such a long time to
generate estimated query plan on some occasions.
Thanks,
IgorIgor,
Are the statistics current and up-to-date?
HTH
Jerry
"imarchenko" <igormarchenko@.hotmail.com> wrote in message
news:uIwoFzZ2FHA.4076@.TK2MSFTNGP09.phx.gbl...
> Hello,
> I am puzzled by following problem. One of our tables has more than 12
> billion rows. Usually, query plan and query itself is executed almost
> immediately but occasionally, it take about 2 minutes to generate
> estimated query execution plan for following query:
> SELECT MAX(qwEventIx) FROM FTE_STREAM_EVENT (NOLOCK)
> There is a PK clustered index defined on qwEventIx field. I do not
> observer any blocking on this object when it takes a long time to
> generate estimated query plan. There is a plan cached in syscacheobjects
> for this query.
> I was wondering if anyone can explain why it takes such a long time to
> generate estimated query plan on some occasions.
> Thanks,
> Igor
>|||It could be that this is when auto-update of statistics occurs. You can catch that in Profiler using
Object, Auto Stats.
--
Tibor Karaszi, SQL Server MVP
http://www.karaszi.com/sqlserver/default.asp
http://www.solidqualitylearning.com/
Blog: http://solidqualitylearning.com/blogs/tibor/
"imarchenko" <igormarchenko@.hotmail.com> wrote in message
news:uIwoFzZ2FHA.4076@.TK2MSFTNGP09.phx.gbl...
> Hello,
> I am puzzled by following problem. One of our tables has more than 12 billion rows. Usually, query
> plan and query itself is executed almost immediately but occasionally, it take about 2 minutes to
> generate estimated query execution plan for following query:
> SELECT MAX(qwEventIx) FROM FTE_STREAM_EVENT (NOLOCK)
> There is a PK clustered index defined on qwEventIx field. I do not observer any blocking on this
> object when it takes a long time to generate estimated query plan. There is a plan cached in
> syscacheobjects for this query.
> I was wondering if anyone can explain why it takes such a long time to generate estimated query
> plan on some occasions.
> Thanks,
> Igor
>|||Tibor,
You were absolutely correct! SQL Server was updating statistics on 12
billion rows table. It was taking over 2 minutes. I suppose it might make
sense to disable AUTOSTATS on this table with sp_autostats and update
statistics manually during off-peak hours. Would you recommend this
approach?
Thanks,
Igor
"Tibor Karaszi" <tibor_please.no.email_karaszi@.hotmail.nomail.com> wrote in
message news:%2311fWFg2FHA.956@.TK2MSFTNGP10.phx.gbl...
> It could be that this is when auto-update of statistics occurs. You can
> catch that in Profiler using Object, Auto Stats.
> --
> Tibor Karaszi, SQL Server MVP
> http://www.karaszi.com/sqlserver/default.asp
> http://www.solidqualitylearning.com/
> Blog: http://solidqualitylearning.com/blogs/tibor/
>
> "imarchenko" <igormarchenko@.hotmail.com> wrote in message
> news:uIwoFzZ2FHA.4076@.TK2MSFTNGP09.phx.gbl...
>> Hello,
>> I am puzzled by following problem. One of our tables has more than 12
>> billion rows. Usually, query plan and query itself is executed almost
>> immediately but occasionally, it take about 2 minutes to generate
>> estimated query execution plan for following query:
>> SELECT MAX(qwEventIx) FROM FTE_STREAM_EVENT (NOLOCK)
>> There is a PK clustered index defined on qwEventIx field. I do not
>> observer any blocking on this object when it takes a long time to
>> generate estimated query plan. There is a plan cached in syscacheobjects
>> for this query.
>> I was wondering if anyone can explain why it takes such a long time to
>> generate estimated query plan on some occasions.
>> Thanks,
>> Igor
>|||Jerry,
It is indeed statistics related.
Thanks,
Igor
"Jerry Spivey" <jspivey@.vestas-awt.com> wrote in message
news:uQmyqVa2FHA.2364@.TK2MSFTNGP12.phx.gbl...
> Igor,
> Are the statistics current and up-to-date?
> HTH
> Jerry
> "imarchenko" <igormarchenko@.hotmail.com> wrote in message
> news:uIwoFzZ2FHA.4076@.TK2MSFTNGP09.phx.gbl...
>> Hello,
>> I am puzzled by following problem. One of our tables has more than 12
>> billion rows. Usually, query plan and query itself is executed almost
>> immediately but occasionally, it take about 2 minutes to generate
>> estimated query execution plan for following query:
>> SELECT MAX(qwEventIx) FROM FTE_STREAM_EVENT (NOLOCK)
>> There is a PK clustered index defined on qwEventIx field. I do not
>> observer any blocking on this object when it takes a long time to
>> generate estimated query plan. There is a plan cached in syscacheobjects
>> for this query.
>> I was wondering if anyone can explain why it takes such a long time to
>> generate estimated query plan on some occasions.
>> Thanks,
>> Igor
>|||Yes, with that long auto.stats time, disabling autostats for that table is reasonable. Make sure you
schedule manual update statistics with a reasonable sample and at a good time (like not before some
big batch, but after :-) ).
--
Tibor Karaszi, SQL Server MVP
http://www.karaszi.com/sqlserver/default.asp
http://www.solidqualitylearning.com/
Blog: http://solidqualitylearning.com/blogs/tibor/
"imarchenko" <igormarchenko@.hotmail.com> wrote in message
news:e1KGDu%232FHA.3420@.TK2MSFTNGP15.phx.gbl...
> Tibor,
> You were absolutely correct! SQL Server was updating statistics on 12 billion rows table. It
> was taking over 2 minutes. I suppose it might make sense to disable AUTOSTATS on this table with
> sp_autostats and update statistics manually during off-peak hours. Would you recommend this
> approach?
> Thanks,
> Igor
>
> "Tibor Karaszi" <tibor_please.no.email_karaszi@.hotmail.nomail.com> wrote in message
> news:%2311fWFg2FHA.956@.TK2MSFTNGP10.phx.gbl...
>> It could be that this is when auto-update of statistics occurs. You can catch that in Profiler
>> using Object, Auto Stats.
>> --
>> Tibor Karaszi, SQL Server MVP
>> http://www.karaszi.com/sqlserver/default.asp
>> http://www.solidqualitylearning.com/
>> Blog: http://solidqualitylearning.com/blogs/tibor/
>>
>> "imarchenko" <igormarchenko@.hotmail.com> wrote in message
>> news:uIwoFzZ2FHA.4076@.TK2MSFTNGP09.phx.gbl...
>> Hello,
>> I am puzzled by following problem. One of our tables has more than 12 billion rows. Usually,
>> query plan and query itself is executed almost immediately but occasionally, it take about 2
>> minutes to generate estimated query execution plan for following query:
>> SELECT MAX(qwEventIx) FROM FTE_STREAM_EVENT (NOLOCK)
>> There is a PK clustered index defined on qwEventIx field. I do not observer any blocking on this
>> object when it takes a long time to generate estimated query plan. There is a plan cached in
>> syscacheobjects for this query.
>> I was wondering if anyone can explain why it takes such a long time to generate estimated query
>> plan on some occasions.
>> Thanks,
>> Igor
>>
>sql

Friday, March 23, 2012

generating sql string for execution

I've a need to generate a condition clause (if statement) from 3 variables: a value, an operator & another value.

To generate this: 'abcd' like 'a%'
& verify if the condition is satisfied I've done the following:

CREATE TABLE #Temp(Result varchar(10))
declare @.cond1 as varchar(50), @.op as varchar(4), @.cond2 as varchar(50),
@.expr as varchar(50),@.result as varchar(10)
set @.cond1 = '''abcd'''
set @.op = 'like'
set @.cond2 = '''a%'''
set @.expr = @.cond1 + ' ' + @.op + ' ' + @.cond2
insert into #temp exec ('select case when ' + @.expr + ' then ''true'' else ''false'' end')
if exists (select result from #temp where result = 'true')
select 'it is true'
else
select 'it is false'
drop table #temp

It works, but a bit clumsy. Is there a more elegant way to do this ?How about something mildly perverse like:DECLARE @.cond1 as varchar(50), @.op as varchar(4), @.cond2 as varchar(50)

SET @.cond1 = '''abcd'''
SET @.op = 'like'
SET @.cond2 = '''a%'''

EXECUTE ('SELECT ''it is '' + CASE WHEN (' + @.cond1 + ' ' + @.op
+ ' ' + @.cond2 + ') THEN ''true'' ELSE ''false'' END')The extra parentheses are just digital "seat belts" in case anything goes wrong cooking up your expression.

-PatP|||Thanks Pat, very creative.

An extension on that: how do I get the result of the execute into a variable ?

with a select one can do this:

declare @.temp as varchar(10)
select @.temp = (select 'abc')
print @.temp

but that doesn't work with an exec

Thanks
Colin|||Now we need to get "creative" to make that happen!DECLARE
@.cond1 AS VARCHAR(50)
, @.cond2 AS VARCHAR(50)
, @.cmd AS NVARCHAR(200)
, @.op AS VARCHAR(4)
, @.result AS NVARCHAR(50)

SET @.cond1 = '''abcd'''
SET @.op = 'like'
SET @.cond2 = '''a%'''

SET @.cmd = 'SELECT @.i = ''it is '' + CASE WHEN (' + @.cond1 + ' ' + @.op
+ ' ' + @.cond2 + ') THEN ''true'' ELSE ''false'' END'

EXECUTE sp_executesql @.cmd, N'@.i NVARCHAR(50) OUTPUT ', @.result OUTPUT

SELECT @.result -- Just to show it worked-PatP

Monday, March 26, 2012

Generation of estimated execution plan takes a long time

Generation of estimated execution plan takes a long time

Generation of estimated execution plan takes a long time

Friday, March 23, 2012

generating sql string for execution

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