SQL Server Execution Plans
Jul 23, 2005
I'm looking for assistance on a problem with SQL Server. We have a
database where a particular query returns about 3000 rows. This query
takes about 2 minutes on most machines, which is fine in this
situation. But on another machine (just one machine), it can run for
over 30 minutes and not return. I ran it in Query Analyzer and it was
returning about 70 rows every 45-90 seconds, which is completely
unacceptable.
(I'm a developer, not a DBA, so bear with me here.)
I ran an estimated execution plan for this database on each machine,
and the "good" one contains lots of parallelism stuff, in particular
the third box in from the left. The "bad" one contains a "Nested Loop"
at that position, and NO parallelism.
We don't know exactly when this started happening, but we DO know that
some security updates have been installed on this machine (it's at the
client location), and also SP1 for Office 2003.
So it looks like parallelism has been turned off by one of these fixes.
Where do we look for how to turn it back on? This is on SQL Server
2000 SP3.
Thanks for any help you might have for me!
Christine Wolak -- SPL WorldGroup --
Join Bytes!
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Jan 13, 2004
In using ADO to connect to SQL Server, I'm trying to retrieve multiple datasets AND statistics that are usually returned via the OnInfoMessage event. For those that are familiar with SQL Server, I need the results returned by the SET STATISTICS IO ON and SET STATISTICS PROFILE ON options. Anyone had any luck doing this before?
Thanks in advance.
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Jul 23, 2005
Hi there - hoping someone can help me here!I have a database that has been underperforming on a number of queriesrecently - in a test environment they take only a few seconds, but onthe live data they take up to a minute or so to run. This is using thesame data.Every evening a copy of the live data is copied to a backup 'snapshot'database on the same server and also, on this copy the queries onlytake a second or so to run. (This is testing through the QueryAnalyser)I've studied the execution plans for the same query on the snapshot dband the live db and they seem to be significantly different - why isthis? it's looking at the same data and exactly the same code!!Anybody got any ideas???
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Dec 7, 2005
Hi I am slowly getting to grips with SQL Server. As a part of this, I have been attempting to work on producing more efficient queries. This post is regarding what appears to be a discrepancy between the SQL Server execution plan and the actual time taken by a query to run. My brief is to produce an attendance system for an education establishment (I presume you know I'm not an A-Level student completing a project :p ). Circa 1.5m rows per annum, testing with ~3m rows currently. College_Year could strictly be inferred from the AttDateTime however it is included as a field because it a part of just about every PK this table is ever likely to be linked to. Indexes are not fully optimised yet. Table:CREATE TABLE [dbo].[AttendanceDets] ([College_Year] [smallint] NOT NULL ,[Group_Code] [char] (12) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL ,[Student_ID] [char] (8) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL ,[Session_Date] [datetime] NOT NULL ,[Start_Time] [datetime] NOT NULL ,[Att_Code] [char] (1) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL ) ON [PRIMARY]GO CREATE CLUSTERED INDEX [IX_AltPK_Clust_AttendanceDets] ON [dbo].[AttendanceDets]([College_Year], [Group_Code], [Student_ID], [Session_Date], [Att_Code]) ON [PRIMARY]GO CREATE INDEX [All] ON [dbo].[AttendanceDets]([College_Year], [Group_Code], [Student_ID], [Session_Date], [Start_Time], [Att_Code]) ON [PRIMARY]GO CREATE INDEX [IX_AttendanceDets] ON [dbo].[AttendanceDets]([Att_Code]) ON [PRIMARY]GOALL inserts are via an overnight sproc - data comes from a third party system. Group_Code is 12 chars (no more no less), student_ID 8 chars (no more no less). I have created a simple sproc. I am using this as a benchmark against which I am testing my options. I appreciate that this sproc is an inefficient jack of all trades - it has been designed as such so I can compare its performance to more specific sprocs and possibly some dynamic SQL. Sproc:CREATE PROCEDURE [dbo].[CAMsp_Att] @College_Year AS SmallInt,@Student_ID AS VarChar(8) = '________', @Group_Code AS VarChar(12) = '____________', @Start_Date AS DateTime = '1950/01/01', @End_Date as DateTime = '2020/01/01', @Att_Code AS VarChar(1) = '_' AS IF @Start_Date = '1950/01/01'SET @Start_Date = CAST(CAST(@College_Year AS Char(4)) + '/08/31' AS DateTime) IF @End_Date = '2020/01/01'SET @End_Date = CAST(CAST(@College_Year +1 AS Char(4)) + '/07/31' AS DateTime) SELECT College_Year, Group_Code, Student_ID, Session_Date, Start_Time, Att_Code FROM dbo.AttendanceDets WHERE College_Year = @College_YearAND Group_Code LIKE @Group_CodeAND Student_ID LIKE @Student_IDAND Session_Date <= @End_DateAND Session_Date >=@Start_DateAND Att_Code LIKE @Att_CodeGOMy confusion lies with running the below script with Show Execution Plan:--SET SHOWPLAN_TEXT ON--Go DECLARE @Time as DateTime Set @Time = GetDate() select College_Year, group_code, Student_ID, Session_Date, Start_Time, Att_Code from attendanceDetswhere College_Year = 2005 AND group_code LIKE '____________' AND Student_ID LIKE '________'AND Session_Date <= '2005-11-16' AND Session_Date >= '2005-11-16' AND Att_Code LIKE '_' Print 'First query took: ' + CAST(DATEDIFF(ms, @Time, GETDATE()) AS VarCHar(5)) + ' milli-Seconds' Set @Time = GetDate() EXEC CAMsp_Att @College_Year = 2005, @Start_Date = '2005-11-16', @End_Date = '2005-11-16' Print 'Second query took: ' + CAST(DATEDIFF(ms, @Time, GETDATE()) AS VarCHar(5)) + ' milli-Seconds'GO --SET SHOWPLAN_TEXT OFF--GOThe execution plan for the first query appears miles more costly than the sproc yet it is effectively the same query with no parameters. However, my understanding is the cached plan substitutes literals for parameters anyway. In any case - the first query cost is listed as 99.52% of the batch, the sproc 0.48% (comparing the IO, cpu costs etc support this). BUT the text output is:(10639 row(s) affected) First query took: 596 milli-Seconds (10639 row(s) affected) Second query took: 2856 milli-SecondsI appreciate that logical and physical performance are not one and the same but can why is there such a huge discrepancy between the two? They are tested on a dedicated test server, and repeated running and switching the order of the queries elicits the same results. Sample data can be provided if requested but I assumed it would not shed much light. BTW - I know that additional indexes can bring the plans and execution time closer together - my question is more about the concept. If you've made it this far - many thanks.If you can enlighten me - infinite thanks.
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Nov 16, 2001
I have two schematically identical databases on the same MS SQL 2000 server. The differences in the data are very slight. Here is my problem: the identical query has totally different execution plans on the different databases. One is (in my opinion) correct, the other causes the query to take 60 times as long. This is not an exaggeration, on the quick DB the query takes 3 seconds, on the other DB it takes 3 minutes. I have tried the following to help the optimizer pick a better execution plan on the slow db:
rebuild the indexes
dbcc indexdefrag
update statistics
I CAN put in a hint to cause the query to execute faster, but my employer now knows about the problem and he (and I) want to know WHY this is happening.
Any ideas would be greatly appreciated.
Thanks.
-Scott
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Jul 23, 2005
HiCan you give me sone pointers to where I can get more information aboutthe various operations like index seeks,Bookmark Lookups,ClusteredIndex Scan in an execution plan.ThanksRagu
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Apr 15, 2008
Hi Gurus,
What permissio0ns one should have to view execution plans on SQL SERVER 2005.
Thanks,
ServerTeam
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Jul 16, 2007
Hi,We are trying to solve a real puzzle. We have a stored procedure thatexhibits *drastically* different execution times depending on how itsexecuted.When run from QA, it can take as little as 3 seconds. When it iscalled from an Excel vba application, it can take up to 180 seconds.Although, at other times, it can take as little as 20 seconds fromExcel.Here's a little background. The 180 second response time *usually*occurs after a data load into a table that is referenced by the storedprocedure.A check of DBCC show_statistics shows that the statistics DO getupdated after a large amount of data is loaded into the table.*** So, my first question is, does the updated statistics force arecompile of the stored procedure?Next, we checked syscacheobjects to see what was going on with theexecution plan for this stored procedure. What I expected to see wasONE execution plan for the stored procedure.This is not the case at all. What is happening is that TWO separateCOMPILED PLANs are being created, depending on whether the sp is runfrom QA or from Excel.In addition, there are several EXECUTABLE PLANs that correspond to thetwo COMPILED PLANs. Depending on *where* the sp is run, the usecountincreases for the various EXECUTABLE PLANS.To me, this does not make any sense! Why are there *multiple* compileand executable plans for the SAME sp?One theory we have is, that we need to call the sp with the dboqualifier, ie) EXEC dbo.spHas anyone seen this? I just want to get to the bottom of this andfind out why sometimes the query takes 180 seconds and other timesonly takes 3 seconds!!Please help.Thanks much
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May 8, 2007
Hi all,
I have a table TableA with few million rows. When I query TableA , the execution plans changes based on the input parameter as shown below . Why this happens ? How to resolve this ? Any inputs would be appreciated.
SELECT * FROM TableA WHERE Column1 = 1 => SELECT -> Clustered Index Scan (100%)
SELECT * FROM TableA WHERE Column1 = 2 => SELECT -> Clustered Index Scan (100%)
SELECT * FROM TableA WHERE Column1 = 3 => SELECT -> Parallelism (3%) -> Clustered Index Scan (97%)
SELECT * FROM TableA WHERE Column1 = 4 => SELECT -> Nested Loops -> Index Seek (50%) -> Clustered Index Seek (50%)
(takes a very long time to retrieve the records)
Thanks in advance,
DBLearner.
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Jun 21, 2006
Does SQLCE 3 cache execution plans? Or even make use of them?
Thanks
Tryst
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Dec 16, 2004
Pls tell me where i will be able to find a good material on interpreting the Execution plans................how do i compare 2 diff plans for Quries written in 2 diff ways...giving same output
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May 16, 2008
I've been working with SQL Server 2005 for a while now and I've noticed some odd behavior that I want to bounce of other members of the community. I should preface that I've been a forum viewer (and occasional contributer) here at SQL Team for a while and I've naturally developed a keen sense for optimizations.
Fundamentally, longer stored procedures with perfectly fine/optimized execution plans are inconsistent with real world performance. In some of these cases, a low subtree cost on a 4 core machine with 16gb of ram and 2 15 drive SAS arrays with little load takes excessively long to run or in some cases doesn't complete.
This isn't due to blocking or resource bottlenecks as I'm quite familiar with built in tools to troubleshoot and resolve those issues. In all cases, I am able to rearchitect the stored procedure into a higher subtree cost variant and get reasonable performance, but it's frustrating to have to redo work and there seems to be no common theme other than longer multi-statement procedures.
I've used SQL Server 2000 extensively and did not notice this level of inconsistency in performance with that product version. Just wondering if others in the community have experiences similar or if I'm just crazy.
Thanks for reading my rant.
- Shane
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Feb 21, 2013
I think not. Microsoft says it is possible: one for parallel and one for serial execution. Don't believe that's possible for a stored procedure to change execution plans on the fly. Have an on-going problem with timeout occurring with an application and narrowed the culprit to a stored procedure. I couldn't find any obvious issues database wise, no locks, etc. so I recompiled (altered) the sproc without making any changes and the issue cleared for a couple days.
It happened again to day, and so I recompiled (altered) the sproc and it went away again. No code changes to both application (so they say) and stored procedure. I ran the below code snippet to check for sprocs with multiple cached plans and the offending one came up on a short list. So, my question is, Is it one sproc per query plan or can there be more than one. I understand the connection issues.
Code:
SELECT db_name(st.dbid) DBName,
object_schema_name(st.objectid, dbid) SchemaName,
object_name(st.objectid, dbid) StoredProcedure,
MAX(cp.usecounts) Execution_count,
st.text [Plan_Text]
INTO #TMP
[Code] .....
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Apr 16, 2008
Anyone know why using
SELECT *
FROM a LEFT OUTER JOIN b
ON a.id = b.id
instead of
SELECT *
FROM a LEFT JOIN b
ON a.id = b.id
generates a different execution plan?
My query is more complex, but when I change "LEFT OUTER JOIN" to "LEFT JOIN" I get a different execution plan, which is absolutely baffling me! Especially considering everything I know and was able to research essentially said the "OUTER" is implied in "LEFT JOIN".
Any enlightenment is very appreciated.
Thanks
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Feb 18, 2000
A year ago one of our SQL Server 6.5 servers was upgraded
to SQL Server 7.0 sp1. My compatibility level still shows
6.5, however. The SQLAgent has been using the 'localsystem'
account up until earlier this week. I changed the login
to be a domain account with System Administrator
permissions and removed the SA permissions from the
BuiltinAdministrator group. (My ultimate goal is to limit
the access NT Administrators have within my SQL databases.) All of my scheduled jobs run without error except the maintenance plans. (All
jobs have an owner of sa.)
The errors that I receive are permission errors-not being able
to get into tables on the MSDB database. However, if I open
Query Analyzer with the SQLAgent domain account and perform
a select on one of the tables in MSDB, it is successful. If I give
the BuiltinAdministrator account the SA permissions again
while still keeping the SQLAgent using the new domain account,
the maintenance jobs succeed.
Is this an upgrade problem since I do have other SQL 7.0 servers
that don't have this problem? How can I correct this?
Thank you!
Toni
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Mar 7, 2008
I am trying to set up a maintenance plan is SQL Server. I set one up to query one of my very small tables for testing purposes. I made sure that I have the server entered in correctly and also verified that I needed to make sure that I have both TCP/IP and Named Pipes both enabled. However, everytime I set something up and try to execute it. The plans ends up failing. This isn't a hard process but something else isn't setup that needs to be. Does anyone have any ideas pertaining to this.
Is there a special credential that needs to be setup for this?
Any help on this would be great. Thanks
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Aug 11, 2015
In SQL 2008 R2, if we clone an environment including SQL server, the maintenance plans retain a connection string to the source/original server they got cloned from and are not editable. But, I was able to use a work around by editing them in BIDS and saving them back on the server. But now with 2014, I am facing two issues:
1.I still can edit the package to correct the server connection, with SSDT; but the option to save back to the server is not available any longer!
2.I used to be able to see all my plans under SSIS in 2008 R2 but not in 2014 now. Although, they are listed in SSMS!
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Nov 28, 2000
I need to know if anybody has any suggestions on websites to visits, documents or templates that will give examples on how to set up a Disaster Recovery Plan for SQL Server 7.0 Databases. I am mostly interested in the Documentation portion to acquire knowledge on the various methodologies used out there. I am a Jr DBA and would appreciate any feedback.
Thanks.
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Apr 21, 2006
If your principal fails and your mirror assumes the main role and it is in Full recovery mode (which it has to be in Standard edition), then the log files will grow and grow until a transaction backup and shrink is executed.
I have maintenance plans running daily (and hourly for transaction log backup/shrink) on my principal, but nothing on my mirror.
Do I need to set up the same maintenance plans on my mirror server???
Thanks
Ed
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Feb 21, 2008
Can anyone please provide me with some Best Practises for setting up Maintenance plans? IE what order should things be done in? What should be done daily, weekly, monthly, yearly... I am attempting to setup a new server and I am now 100% sure I have the maintenance plan setup correctly... expecially when I attempted to run it last night it and ran for over 8 hours and still didn't do the backup's yet. I had to reboot the server this morning to make it stop using 100% of the CPU. So please any help would be wonderful.
Regards,
Billy S.
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Apr 30, 2014
way to invalidate cached query plans? I would rather target a specific query instead of invalidating all of them.
Also do you know of any sql server setting that will cause cached query plans to invalidate even though only one character in the queries has changed?
exec sp_executesql N'select
cast(5 as int) as DisplaySequence,
mt.Description + '' '' + ct.Description as Source,
[Code].....
In this query we have seen (on some databases) simply changing ‘@CustomerId int',@CustomerId=1065’ too ‘@customerId int',@customerId=1065’ fixed the a speed problem….just changed the case on the Customer bind parameter. On other servers this has no effect. I’m thinking the server is using an old cached query plan, but don’t know for sure.
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Aug 10, 2007
I've seen a few threads on this which seem to suppose the problem is on Express edition rather than Standard edition. Not so here.
This is definitely Standard edition, SP3 as seen by running
SELECT CONVERT(char(20), SERVERPROPERTY('Edition'))
SELECT CONVERT(char(20), SERVERPROPERTY('ProductLevel'))
In SSMS
Under the Management folder there is no "Maintenance Plans" folder.
There IS a "Maintenance Plans" folder under the Legacy Folder.
I have another instance which is Standard and SP1 which looks just fine.
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Nov 18, 2007
I have a SQL Server 2005 x64 bit with SP2 applied and patched to KB934458-x64-ENU (9.0.3054)
I am unable to create a maintenance plan via Management Studio or save a plan in Management Studio using the wizard.
If I just try and create a new maintenance plan, then I get the following problem:
"An OLE DB error 0x80004005 (Login timeout expired) occurred while enumerating packages. A SQL statement was issued and failed."
If I try and create any maintenance plan via the wizard, I get the following problem:
"The SaveToSQLServer method has encountered OLE DB error code 0x80004005 (Login timeout expired). The SQL statement that was issued has failed."
I've doen a bit of digging on this and had initially thought it was related to the fact that I have two instances installed on 1 server. I've since updated the MsDtsSrvr.ini.xml file to point at both instances, as I thought that might have been causing the problem. That hasn't helped at all. Edited example of xml file is below:
<?xml version="1.0" encoding="utf-8"?><DtsServiceConfiguration xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"> <StopExecutingPackagesOnShutdown>true</StopExecutingPackagesOnShutdown> <TopLevelFolders> <Folder xsi:type="SqlServerFolder"> <Name>MSDB SQL Server Instance 1</Name> <ServerName>ServerNameInstanceName1</ServerName> </Folder> <Name>MSDB Server Instance 2</Name> <ServerName>ServerNameInstanceName2</ServerName> </Folder> <Folder xsi:type="FileSystemFolder"> <Name>File System</Name> <StorePath>..Packages</StorePath> </Folder> </TopLevelFolders> </DtsServiceConfiguration>
Any suggestions would be most welcome!
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Aug 19, 2015
I often use profiler as one tool to identify bad plans. The reads column gives me a good indication of excessive IO to dig into and correct if necessary. I often use it with Showplan so I can see what a query does, replicate it and fix it.
However I have just lost some faith in it. I am looking at a poorly performing query joining five tables. A parallel plan has been generated and one table is being scanned (in parallel) due to a missing index. This table had in excess of 4 million rows in it. The rest hitd indexes well. However the entire query generates ONLY 12 READS.
Once corrected, a single processor plan is used. This looks really efficient and uses 120 reads. That looks the right figure to me.
Clearly 12 reads is wrong. Does the profiler only display one thread of a parallel plan perhaps? Or something else?
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Aug 23, 2007
after moving off VS debugger and into management studio to exercise our SQLCLR sp, we notice that the 2nd execution gets an error suggesting that our static SqlCommand object is getting reused from the 1st execution (of the sp under mgt studio). If this is expected behavior, we have no problem limiting our statics to only completely reusable objects but would first like to know if this is expected? Is the fact that debugger doesnt show this behavior also expected?
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Aug 3, 2007
Hello :
How to execute a procedure stored during execution of the report, that is before the poster the data.
Thnak you.
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Nov 29, 2004
Here's my case, I have written a stored procedure which will perform the following:
1. Grab data from a table using cursor,
2. Process data,
3. Write the result into another table
If I execute the stored procedure directly (thru VS.NET, or Query Analyser), it will run, but when I tried to execute it via a scheduled job, it fails.
I used the same record, same parameters, and the same statements to call the stored procedure.
Any idea?
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Feb 20, 2003
SQL7: I have added a Maintenance Plan to backup to 4mm dat tape the master and msdb SQL databases as well as another database relative to our application called WISE. This works fine; however, it appears to always append to the media as opposed to overwriting (preferred). Any help would be appreciated.....
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Aug 22, 2005
Hi,
I am going to set up maintenance plans on all our SQL servers (7.0 and 2000). I have found several 'tutorials' on how to do this, but no one is describing the options in detail. Can you guys/gals please help me out? We have alot of small databases and some medium (1-2GB).
Thanks//Stefan
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May 14, 2002
I am new to SQL Server 2000 & need ya all's help!!
I am trying to set up a database maintenance plan to back up databases & transactional logs. If I do a full backup once a week & a transactional backup every day...will I be safe enough to have enough backups to be able to restore to any point of time by restoring the full backup & the transactional logs upto that point?
In other words, I am asking what are the points to consider & what should be a decent backup plan? Do transactional logs take stored procedureal changes also?
Thanks for ur help,
Edward
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Feb 15, 2005
We have Veritas' Backupexec running in our Enterprise and the Veritas Install actually installs MS SQL Server MSDN on each Server in the Enterprise.
It looks like it also sets up a default Maintenance plan within each of the MSDN Instances.
I guess my question is.. Can I manage the Maintenance Plans on these MSDN Instances via the SQL Server EM GUI from my desktop?? Seems like when I look at the Maintenance plans alot of the options are greyed out or not available. What I am trying to do is modify one of the maintenance plans to have the backups deleted after one week (One of the Instances has been running a complete backup on the Backupexec Databases for a year and there are a years worth of backups on the Server) but the option to "remove files older than" is 'greyed out' ??????
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Feb 20, 2008
Eh uhhhh where did the old '-DelBkUps 7DAYS' (delete files older than 7 Days) option go?
Is this a future product enhancement?
I fee like such a dirty noob.
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Dec 1, 2007
Does anyone get any issues creating "Backup" jobs as a Maintenance Plan when specifying the backup location as a UNC path (e.g. "\backup_bladeBACKUPS")?
For some reason, if i try using the UNC path for a 1-time backup, it works, but when I am trying to put it into a scheduled job, it does not 'seem' to perform the Backup step.
Help please...
seethem
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